PcpA of Streptococcus pneumoniae mediates adherence to nasopharyngeal and lung epithelial cells and elicits functional antibodies in humans

Streptococcus pneumoniae serotype distribution in low- and middle-income countries of South Asia: Do we need to revisit the pneumococcal vaccine strategy?

S. pneumoniae serotypes responsible for pneumococcal disease differ with respect to disease severity, invasiveness, antimicrobial susceptibility, geographies, immunization history, age groups, and with time. Although PCVs have blunted the pneumococcal disease burden, they are plagued with numerous challenges, especially the emergence of NVTs. In this review, we show that there are diverse serotypes, especially NVTs, responsible for causing pneumococcal diseases in LMICs of South Asia across different studies conducted between 2012 and 2024. We propose that pharmaceutical/biotech companies should tailor/customize the PCVs as per the region-specific serotype prevalence based on surveillance data. Furthermore, protein-based vaccines, or WCVs, have been explored and can serve as viable alternatives to address the limitations associated with PCVs. However, robust studies are warranted in different geographies to demonstrate its efficacy and safety in clinical trials as well as the real-world effectiveness of these promising candidates.

Future immunisation strategies to prevent Streptococcus pneumoniae infections in children and adults

Streptococcus pneumoniae is a major respiratory pathogen, causing 1·2 million deaths and 197 million pneumonia episodes globally in 2016. The spread of S pneumoniae to sterile sites, such as the blood and brain, leads to invasive pneumococcal disease. The best approach available for prevention of invasive pneumococcal disease in children and, more recently, adults is the use of pneumococcal conjugate vaccines (PCVs). PCVs are also highly effective at preventing colonisation and, thus, transmission, offering indirect protection to non-target immunisation groups such as adults-a characteristic that has been crucial in their success. However, PCVs only include and protect up to 20 of the 100 serotypes that can cause disease. The rise in adult cases of invasive pneumococcal disease from serotypes included in PCVs suggests indirect protection might be limited. Additionally, non-vaccine serotypes and some vaccine types that persist, some linked to antibiotic resistance, continue to cause disease. Future vaccine strategies include increasing the number of serotypes covered in PCVs for use in children and adults, broader vaccine use in adults, the development of adult-specific conjugate vaccines containing serotypes different from those covered in PCVs used in children, and protein vaccines, all of which will be explored in this Review. These strategies are expected to help mitigate the global burden of invasive pneumococcal disease in future years.

The global transcriptional regulator MgaSpn affects the virulence of Streptococcus pneumoniae by regulating PcpA

The global transcriptional regulator MgaSpn is a significant virulence factor of Streptococcus pneumoniae. In our previous study, we found that MgaSpn is a regulator of bacterial virulence by modulating the levels of phosphorylcholine (ChoP) and capsular polysaccharides (CPS) on the surface of S. pneumoniae. Here, we report for the first time that pcpA expression was significantly increased in mgaSpn deletion strains and significantly decreased when mgaSpn was overexpressed. Electrophoretic mobility-shift and DNase I footprinting assays confirmed that MgaSpn interacts with the pcpA promoter (PpcpA) at two specific binding sites. Virulence experiments demonstrated that the interaction between MgaSpn and PcpA is necessary for pneumococcal colonization and invasive infection. Western blot analysis indicated that iron concentration can influences the regulation of PcpA expression via MgaSpn. In summary, these results revealed that MgaSpn regulates PcpA and plays a significant role in pneumococcal pathogenesis.

Putative pathogenic factors underlying Streptococcus oralis opportunistic infections

Streptococcus oralis, belonging to the viridans group streptococci (VGS), has been considered a component of the normal flora predominantly inhabiting the oral cavity. In recent years, a growing body of literature has revealed that dental procedures or daily tooth brushing activities can cause the spread of S. oralis from the oral cavity into various body sites leading to life-threatening opportunistic infections such as infective endocarditis (IE) and meningitis. However, very little is currently known about the pathogenicity of S. oralis. Thus, the aim of this review is to update the current understanding of the pathogenic potential of S. oralis to pave the way for the prevention and treatment of S. oralis opportunistic infections.

Impact of Endogenous Pneumococcal Hydrogen Peroxide on the Activity and Release of Pneumolysin

Streptococcus pneumoniae is the leading cause of community-acquired pneumonia. The pore-forming cholesterol-dependent cytolysin (CDC) pneumolysin (PLY) and the physiological metabolite hydrogen peroxide (H2O2) can greatly increase the virulence of pneumococci. Although most studies have focused on the contribution of both virulence factors to the course of pneumococcal infection, it is unknown whether or how H2O2 can affect PLY activity. Of note, S. pneumoniae exploits endogenous H2O2 as an intracellular signalling molecule to modulate the activity of several proteins. Here, we demonstrate that H2O2 negatively affects the haemolytic activity of PLY in a concentration-dependent manner. Prevention of cysteine-dependent sulfenylation upon substitution of the unique and highly conserved cysteine residue to serine in PLY significantly reduces the toxin's susceptibility to H2O2 treatment and completely abolishes the ability of DTT to activate PLY. We also detect a clear gradual correlation between endogenous H2O2 generation and PLY release, with decreased H2O2 production causing a decline in the release of PLY. Comparative transcriptome sequencing analysis of the wild-type S. pneumoniae strain and three mutants impaired in H2O2 production indicates enhanced expression of several genes involved in peptidoglycan (PG) synthesis and in the production of choline-binding proteins (CPBs). One explanation for the impact of H2O2 on PLY release is the observed upregulation of the PG bridge formation alanyltransferases MurM and MurN, which evidentially negatively affect the PLY release. Our findings shed light on the significance of endogenous pneumococcal H2O2 in controlling PLY activity and release.

TCS01 Two-Component System Influenced the Virulence of Streptococcus pneumoniae by Regulating PcpA

Streptococcus pneumoniae relies on two-component systems (TCSs) to regulate the processes of pathogenicity, osmotic pressure, chemotaxis, and energy metabolism. The TCS01 system of S. pneumoniae is composed of HK01 (histidine kinase) and RR01 (response regulator). Previous studies have reported that an rr01 mutant reduced the pneumococcal virulence in rat pneumonia, bacteremia, a nasopharyngeal model, and infective endocarditis. However, the mechanism of TCS01 (HK/RR01) regulating pneumococcal virulence remains unclear. Here, pneumococcal mutant strains Δrr01, Δhk01, and Δrr01&hk01 were constructed, and bacterial adhesion and invasion to A549 cells were compared. RNA sequencing was performed in D39 wild-type and Δrr01 strains, and transcript profile changes were analyzed. Differentially expressed virulence genes in the Δrr01 strain were screened out and identified by quantitative real-time PCR (qRT-PCR). Our results showed that pneumococcal mutant strains exhibited attenuated adhesion and invasion to A549 cells and differential transcript profiles. Results of qRT-PCR identification showed that the differential virulence genes screened out were downregulated. Among those changed virulence genes in the Δrr01 strain, the downregulated expression level of choline binding protein pcpA was the most obvious. Complementation of rr01 and overexpression of pcpA in the Δrr01 strain partially restored both pneumococcal adhesion and invasion, and rr01 complementation made the expression of pcpA upregulated. These findings revealed that rr01 influenced pneumococcal virulence by regulating pcpA.

The Two-Component System YesMN Promotes Pneumococcal Host-to-Host Transmission and Regulates Genes Involved in Zinc Homeostasis

The ability to sense and respond rapidly to the dynamic environment of the upper respiratory tract (URT) makes Streptococcus pneumoniae (Spn) a highly successful human pathogen. Two-component systems (TCSs) of Spn sense and respond to multiple signals it encounters allowing Spn to adapt and thrive in various host sites. Spn TCS have been implicated in their ability to promote pneumococcal colonization of the URT and virulence. As the disease state can be a dead-end for a pathogen, we considered whether TCS would contribute to pneumococcal transmission. Herein, we determined the role of YesMN, an understudied TCS of Spn, and observe that YesMN contributes toward pneumococcal shedding and transmission but is not essential for colonization. The YesMN regulon includes genes involved in zinc homeostasis and glycan metabolism, which are upregulated during reduced zinc availability in a YesMN-dependent fashion. Thus, we identified the YesMN regulon and a potential molecular signal it senses that lead to the activation of genes involved in zinc homeostasis and glycan metabolism. Furthermore, in contrast to Spn monoinfection, we demonstrate that YesMN is critical for high pneumococcal density in the URT during influenza A virus (IAV) coinfection. We attribute reduced colonization of the yesMN mutant possibly due to increased association with and clearance by the mucus covering the URT epithelial surface. Thus, our results highlight the dynamic interactions that occur between Spn and IAV in the URT, and the role that TCSs play in modulation of these interactions.

Diverse Mechanisms of Protective Anti-Pneumococcal Antibodies

The gram-positive bacterium Streptococcus pneumoniae is a leading cause of pneumonia, otitis media, septicemia, and meningitis in children and adults. Current prevention and treatment efforts are primarily pneumococcal conjugate vaccines that target the bacterial capsule polysaccharide, as well as antibiotics for pathogen clearance. While these methods have been enormously effective at disease prevention and treatment, there has been an emergence of non-vaccine serotypes, termed serotype replacement, and increasing antibiotic resistance among these serotypes. To combat S. pneumoniae, the immune system must deploy an arsenal of antimicrobial functions. However, S. pneumoniae has evolved a repertoire of evasion techniques and is able to modulate the host immune system. Antibodies are a key component of pneumococcal immunity, targeting both the capsule polysaccharide and protein antigens on the surface of the bacterium. These antibodies have been shown to play a variety of roles including increasing opsonophagocytic activity, enzymatic and toxin neutralization, reducing bacterial adherence, and altering bacterial gene expression. In this review, we describe targets of anti-pneumococcal antibodies and describe antibody functions and effectiveness against S. pneumoniae.

Streptococcus pneumoniae binds to host GAPDH on dying lung epithelial cells worsening secondary infection following influenza

Streptococcus pneumoniae (Spn) alone and during co-infection with influenza A virus (IAV) can result in severe pneumonia with mortality. Pneumococcal surface protein A (PspA) is an established virulence factor required for Spn evasion of lactoferricin and C-reactive protein-activated complement-mediated killing. Herein, we show that PspA functions as an adhesin to dying host cells. We demonstrate that PspA binds to host-derived glyceraldehyde-3-phosphate dehydrogenase (GAPDH) bound to outward-flipped phosphatidylserine residues on dying host cells. PspA-mediated adhesion was to apoptotic, pyroptotic, and necroptotic cells, but not healthy lung cells. Using isogenic mutants of Spn, we show that PspA-GAPDH-mediated binding to lung cells increases pneumococcal localization in the lower airway, and this is enhanced as a result of pneumolysin exposure or co-infection with IAV. PspA-mediated binding to GAPDH requires amino acids 230-281 in its α-helical domain with intratracheal inoculation of this PspA fragment alongside the bacteria reducing disease severity in an IAV/Spn pneumonia model.

Comparison of specific in-vitro virulence gene expression and innate host response in locally invasive vs colonizer strains of Streptococcus pneumoniae

Among Rochester NY children, a dramatic increase in nasopharyngeal (NP) colonization by non-vaccine pneumococcal serotypes 35B and 15A occurred during years 2010-2015, after introduction of 13-valent pneumococcal conjugate vaccine (PCV13). In our population, serotype 35B strains colonized in the nasopharynx (NP) but infrequently caused acute otitis media (AOM) whereas serotype 15A strains displayed virulence, evidenced by causing AOM. To explain the virulence difference, virulence genes expression between 35B and 15A, as well as the host's immune response during asymptomatic colonization were analyzed. We investigated differences in regulation of 19 virulence genes for differences in virulence using RT-PCR in 20 35B and 14 15A strains and measured gene expression of 9 host innate cytokines in the NP to assess the mucosal inflammatory response during asymptomatic colonization. Comparing 35B versus 15A strains, genes for competence ComA and RrgC were upregulated; capsular (Cps2D) and virulence genes (PfbA, PcpA and PhtE) were downregulated among 35B strains. PavB, LytA, LytB, NanA, CiaR, PhtD, LuxS, PspA and pneumolysin (Ply) showed no difference. IL17 and IL23 gene expression were > tenfold higher during 35B compared to 15A strain asymptomatic colonization. Only IL23 showed significant difference. In the first 5 years after introduction of PCV13, serotype 35B strains emerged as asymptomatic colonizers and 15A strains emerged to cause AOM in young children. Various genes (PfbA, PcpA, Cps2D and PhtE) among tested in this analysis were downregulated in 35B whereas ComA and RrgC were significantly upregulated. For the host's cytokine response, IL23 proinflammatory response which is essential for the differentiation of Th17 lymphocytes in the NP of children with 35B strains was significantly higher than the response to 15A during asymptomatic colonization.

Multi-Valent Protein Hybrid Pneumococcal Vaccines: A Strategy for the Next Generation of Vaccines

Streptococcus pneumoniae (Spn) is a bacterial pathogen known to colonize the upper respiratory tract and cause serious opportunistic diseases such as pneumonia, bacteremia, sepsis and meningitis. As a consequence, millions of attributable deaths occur annually, especially among infants, the elderly and immunocompromised individuals. Although current vaccines, composed of purified pneumococcal polysaccharide in free form or conjugated to a protein carrier, are widely used and have been demonstrated to be effective in target groups, Spn has continued to colonize and cause life-threatening disease in susceptible populations. This lack of broad protection highlights the necessity of improving upon the current "gold standard" pneumococcal vaccines to increase protection both by decreasing colonization and reducing the incidence of sterile-site infections. Over the past century, most of the pneumococcal proteins that play an essential role in colonization and pathogenesis have been identified and characterized. Some of these proteins have the potential to serve as antigens in a multi-valent protein vaccine that confers capsule independent protection. This review seeks to summarize the benefits and limitations of the currently employed vaccine strategies, describes how leading candidate proteins contribute to pneumococcal disease development, and discusses the potential of these proteins as protective antigens-including as a hybrid construct.

Multipathogen Analysis of IgA and IgG Antigen Specificity for Selected Pathogens in Milk Produced by Women From Diverse Geographical Regions: The INSPIRE Study

Breastfeeding provides defense against infectious disease during early life. The mechanisms underlying this protection are complex but likely include the vast array of immune cells and components, such as immunoglobulins, in milk. Simply characterizing the concentrations of these bioactives, however, provides only limited information regarding their potential relationships with disease risk in the recipient infant. Rather, understanding pathogen and antigen specificity profiles of milk-borne immunoglobulins might lead to a more complete understanding of how maternal immunity impacts infant health and wellbeing. Milk produced by women living in 11 geographically dispersed populations was applied to a protein microarray containing antigens from 16 pathogens, including diarrheagenic E. coli, Shigella spp., Salmonella enterica serovar Typhi, Staphylococcus aureus, Streptococcus pneumoniae, Mycobacterium tuberculosis and other pathogens of global health concern, and specific IgA and IgG binding was measured. Our analysis identified novel disease-specific antigen responses and suggests that some IgA and IgG responses vary substantially within and among populations. Patterns of antibody reactivity analyzed by principal component analysis and differential reactivity analysis were associated with either lower-to-middle-income countries (LMICs) or high-income countries (HICs). Antibody levels were generally higher in LMICs than HICs, particularly for Shigella and diarrheagenic E. coli antigens, although sets of S. aureus, S. pneumoniae, and some M. tuberculosis antigens were more reactive in HICs. Differential responses were typically specific to canonical immunodominant antigens, but a set of nondifferential but highly reactive antibodies were specific to antigens possibly universally recognized by antibodies in human milk. This approach provides a promising means to understand how breastfeeding and human milk protect (or do not protect) infants from environmentally relevant pathogens. Furthermore, this approach might lead to interventions to boost population-specific immunity in at-risk breastfeeding mothers and their infants.

Understanding host immune responses to pneumococcal proteins in the upper respiratory tract to develop serotype-independent pneumococcal vaccines

Introduction: Nasopharyngeal colonization is a precondition for mucosal and invasive pneumococcal disease. Prevention of colonization may reduce pneumococcal transmission and disease incidence. Therefore, several protein-based pneumococcal vaccines are currently under investigation. Areas covered: We aimed to better understand the host immune responses to pneumococcal proteins in the upper respiratory tract (URT) that could facilitate the development of serotype-independent pneumococcal vaccines. English peer-reviewed papers reporting immunological mechanisms involved in host immune response to pneumococcal proteins in the URT were retrieved through a PubMed search using the terms 'pneumococcal proteins,' 'nasopharyngeal colonization' and/or 'cellular/humoral host immune response.' Expert opinion: Although pneumococcal protein antigens induce humoral immune responses, as well as IL-17A-mediated immunity, none of them, when used as single antigen, is sufficient to control and broadly protect against pneumococcal colonization. Novel vaccines should contain multiple conserved protein antigens to activate both arms of the immune system and evoke protection against the whole spectrum of pneumococcal variants by reducing, rather than eradicating, pneumococcal carriage. The highest efficacy would likely be achieved when the vaccine is intranasally applied, inducing mucosal immunity and enhancing the first line of defense by restricting pneumococcal density in the URT, which in turn will lead to reduced transmission and protection against disease.

State-of-the-art in the pneumococcal field: Proceedings of the 11th International Symposium on Pneumococci and Pneumococcal Diseases (ISPPD-11)

The International Symposium on Pneumococci and Pneumococcal Diseases (ISPPD) is the premier global scientific symposium dedicated to the exchange, advancement and dissemination of the latest research on the pneumococcus, one of the world's deadliest bacterial pathogens. Since the first ISPPD was held in 1998, substantial progress has been made to control pneumococcal disease, for instance, more than half of surviving infants (78.6 million) from 143 countries now have access to the life-saving pneumococcal conjugate vaccine (PCV). The 11th ISPPD (ISPPD-11) was held in Melbourne, Australia in April 2018 and the proceedings of the symposium are captured in this report. Twenty years on from the first ISPPD, there remain many challenges and unanswered questions such as the continued disparity in disease incidence in Indigenous populations, the slow roll-out of PCV in some regions such as Asia, the persisting burden of disease in adults, serotype replacement and diagnosis of pneumococcal pneumonia. ISPPD-11 also put the spotlight on cutting-edge science including metagenomic, transcriptomic, microscopy, medical imaging and mathematical modelling approaches. ISPPD-11 was highly diverse, bringing together 1184 delegates from 86 countries, representing various fields including academia, primary healthcare, pharmaceuticals, biotechnology, policymakers and public health.

Identification of Virulence-Associated Properties by Comparative Genome Analysis of Streptococcus pneumoniae, S. pseudopneumoniae, S. mitis, Three S. oralis Subspecies, and S. infantis

Streptococcus pneumoniae is one of the most important human pathogens but is closely related to Streptococcus mitis, with which humans live in harmony. The fact that the two species evolved from a common ancestor provides a unique basis for studies of both infection-associated properties and properties important for harmonious coexistence with the host. By detailed comparisons of genomes of the two species and other related streptococci, we identified 224 genes associated with virulence and 25 genes unique to the mutualistic species. The exclusive presence of the virulence factors in S. pneumoniae enhances their potential as vaccine components, as a direct impact on beneficial members of the commensal microbiota can be excluded. Successful adaptation of S. mitis and other commensal streptococci to a harmonious relationship with the host relied on genetic stability and properties facilitating life in biofilms.

From a common ancestor, Streptococcus pneumoniae and Streptococcus mitis evolved in parallel into one of the most important pathogens and a mutualistic colonizer of humans, respectively. This evolutionary scenario provides a unique basis for studies of both infection-associated properties and properties important for harmonious coexistence with the host. We performed detailed comparisons of 60 genomes of S. pneumoniae, S. mitis, Streptococcus pseudopneumoniae, the three Streptococcus oralis subspecies oralis, tigurinus, and dentisani, and Streptococcus infantis. Nonfunctional remnants of ancestral genes in both S. pneumoniae and in S. mitis support the evolutionary model and the concept that evolutionary changes on both sides were required to reach their present relationship to the host. Confirmed by screening of >7,500 genomes, we identified 224 genes associated with virulence. The striking difference to commensal streptococci was the diversity of regulatory mechanisms, including regulation of capsule production, a significantly larger arsenal of enzymes involved in carbohydrate hydrolysis, and proteins known to interfere with innate immune factors. The exclusive presence of the virulence factors in S. pneumoniae enhances their potential as vaccine components, as a direct impact on beneficial members of the commensal microbiota can be excluded. In addition to loss of these virulence-associated genes, adaptation of S. mitis to a mutualistic relationship with the host apparently required preservation or acquisition of 25 genes lost or absent from S. pneumoniae. Successful adaptation of S. mitis and other commensal streptococci to a harmonious relationship with the host relied on genetic stability and properties facilitating life in biofilms.

The transcriptomic response of Streptococcus pneumoniae following exposure to cigarette smoke extract

Exposure to cigarette smoke is a risk factor for respiratory diseases. Although most research has focused on its effects on the host, cigarette smoke can also directly affect respiratory pathogens, in some cases enhancing virulence. Streptococcus pneumoniae (the pneumococcus) is a leading cause of community-acquired pneumonia worldwide, however data on the effects of cigarette smoke on the pneumococcus are sparse. Using RNA-seq, we show that pneumococci exposed to cigarette smoke extract in a concentrated acute exposure in vitro model initiate a 'survival' transcriptional response including the upregulation of detoxification enzymes, efflux pumps and osmoregulator transporters, as well as the downregulation of fatty acid and D-alanyl lipoteichoic acid biosynthesis genes. Except for the downregulation of the pneumolysin gene, there were no changes in the expression of major virulence factors following exposure to cigarette smoke. Compared to unexposed pneumococci, smoke-exposed pneumococci did not exhibit any changes in viability, adherence, hydrophobicity or cell lysis susceptibility. In this study, we demonstrate that pneumococci adapt to acute noxious cigarette smoke exposure by inducing a gene expression signature that allows the bacteria to resist its harmful effects.

Functional insights from proteome-wide structural modeling of Treponema pallidum subspecies pallidum, the causative agent of syphilis

Background

Syphilis continues to be a major global health threat with 11 million new infections each year, and a global burden of 36 million cases. The causative agent of syphilis, Treponema pallidum subspecies pallidum, is a highly virulent bacterium, however the molecular mechanisms underlying T. pallidum pathogenesis remain to be definitively identified. This is due to the fact that T. pallidum is currently uncultivatable, inherently fragile and thus difficult to work with, and phylogenetically distinct with no conventional virulence factor homologs found in other pathogens. In fact, approximately 30% of its predicted protein-coding genes have no known orthologs or assigned functions. Here we employed a structural bioinformatics approach using Phyre2-based tertiary structure modeling to improve our understanding of T. pallidum protein function on a proteome-wide scale.

Results

Phyre2-based tertiary structure modeling generated high-confidence predictions for 80% of the T. pallidum proteome (780/978 predicted proteins). Tertiary structure modeling also inferred the same function as primary structure-based annotations from genome sequencing pipelines for 525/605 proteins (87%), which represents 54% (525/978) of all T. pallidum proteins. Of the 175 T. pallidum proteins modeled with high confidence that were not assigned functions in the previously annotated published proteome, 167 (95%) were able to be assigned predicted functions. Twenty-one of the 175 hypothetical proteins modeled with high confidence were also predicted to exhibit significant structural similarity with proteins experimentally confirmed to be required for virulence in other pathogens.

Conclusions

Phyre2-based structural modeling is a powerful bioinformatics tool that has provided insight into the potential structure and function of the majority of T. pallidum proteins and helped validate the primary structure-based annotation of more than 50% of all T. pallidum proteins with high confidence. This work represents the first T. pallidum proteome-wide structural modeling study and is one of few studies to apply this approach for the functional annotation of a whole proteome.

Electronic supplementary material

The online version of this article (10.1186/s12900-018-0086-3) contains supplementary material, which is available to authorized users.

Determination of avidity of IgG against protein antigens from Streptococcus pneumoniae: assay development and preliminary application in clinical settings

The measurement of antibody levels is a common test for the diagnosis of Streptococcus pneumoniae infection in research. However, the quality of antibody response, reflected by avidity, has not been adequately evaluated. We aimed to evaluate the role of avidity of IgG against eight pneumococcal proteins in etiologic diagnosis. Eight pneumococcal proteins (Ply, CbpA, PspA1 and 2, PcpA, PhtD, StkP-C, and PcsB-N) were used to develop a multiplex bead-based avidity immunoassay. The assay was tested for effects of the chaotropic agent, multiplexing, and repeatability. The developed assay was applied to paired samples from children with or without pneumococcal disease (n = 38 for each group), determined by either serology, polymerase chain reaction (PCR), or blood culture. We found a good correlation between singleplex and multiplex assays, with r ≥ 0.94.The assay was reproducible, with mean inter-assay variation ≤ 9% and intra-assay variation < 6%. Children with pneumococcal disease had lower median avidity indexes in the acute phase of disease for PspA1 and 2 (p = 0.042), PcpA (p = 0.002), PhtD (p = 0.014), and StkP-C (p < 0.001). When the use of IgG avidity as a diagnostic tool for pneumococcal infection was evaluated, the highest discriminative power was found for StkP-C, followed by PcpA (area under the curve [95% confidence interval, CI]: 0.868 [0.759-0.977] and 0.743 [0.607-879], respectively). The developed assay was robust and had no deleterious influence from multiplexing. Children with pneumococcal disease had lower median avidity against five pneumococcal proteins in the acute phase of disease compared to children without disease.

Panel 6: Vaccines

Objective To review the literature on progress regarding (1) effectiveness of vaccines for prevention of otitis media (OM) and (2) development of vaccine antigens for OM bacterial and viral pathogens. Data Sources PubMed database of the National Library of Science. Review Methods We performed literature searches in PubMed for OM pathogens and candidate vaccine antigens, and we restricted the searches to articles in English that were published between July 2011 and June 2015. Panel members reviewed literature in their area of expertise. Conclusions Pneumococcal conjugate vaccines (PCVs) are somewhat effective for the prevention of pneumococcal OM, recurrent OM, OM visits, and tympanostomy tube insertions. Widespread use of PCVs has been associated with shifts in pneumococcal serotypes and bacterial pathogens associated with OM, diminishing PCV effectiveness against AOM. The 10-valent pneumococcal vaccine containing Haemophilus influenzae protein D (PHiD-CV) is effective for pneumococcal OM, but results from studies describing the potential impact on OM due to H influenzae have been inconsistent. Progress in vaccine development for H influenzae, Moraxella catarrhalis, and OM-associated respiratory viruses has been limited. Additional research is needed to extend vaccine protection to additional pneumococcal serotypes and other otopathogens. There are likely to be licensure challenges for protein-based vaccines, and data on correlates of protection for OM vaccine antigens are urgently needed. Implications for Practice OM continues to be a significant health care burden globally. Prevention is preferable to treatment, and vaccine development remains an important goal. As a polymicrobial disease, OM poses significant but not insurmountable challenges for vaccine development.

Correlation of higher antibody levels to pneumococcal proteins with protection from pneumococcal acute otitis media but not protection from nasopharyngeal colonization in young children

OBJECTIVES

We previously found that nasopharyngeal (NP) colonization by Streptococcus pneumoniae elicits mucosal antibody responses to three protein vaccine candidates: pneumococcal histidine triad protein D (PhtD), pneumococcal choline-binding protein A (PcpA), and detoxified pneumolysin (PlyD1). Here we sought to determine if mucosal antibody levels to the proteins correlated with protection from acute otitis media (AOM) and NP colonization.

METHODS

A total of 228 NP samples were prospectively collected from 100 healthy infants at 6-24 months of age. Whenever children were diagnosed with AOM, middle ear fluids were collected to confirm the diagnosis by microbiological culture. NP mucosal IgG and IgA were quantified by ELISA.

RESULTS

Higher NP mucosal antibody levels to S. pneumoniae proteins correlated with significantly decreased likelihood of developing AOM caused by S. pneumoniae during 3 to 12 months of subsequent prospective monitoring. Specifically, children who did not experience AOM (n=111samples) caused by S. pneumoniae had two- to five-fold higher mucosal IgG levels to PcpA (all p values <0.01), six- to eight-fold higher IgA to PhtD (all p values <0.05); two- to three-folder higher IgA to PcpA (all p values <0.05), and two- to three-fold higher IgA to PlyD1 (p 0.08, p 0.03 and p 0.08) compared with children who did experience AOM (n=18samples). No association between mucosal antibody levels to the three proteins and NP colonization with S. pneumoniae was found.

CONCLUSION

Higher NP mucosal IgG levels to PcpA, and IgA to PhtD, PcpA and PlyD1 correlate with reduced risk of development of S. pneumoniae AOM infection but not with reduced risk of NP colonization in young children.

Rationale and prospects for novel pneumococcal vaccines

Streptococcus pneumoniae remains one of the most frequent bacterial causes of morbidity and mortality worldwide. National immunization programs implementing pneumococcal polysaccharide conjugate vaccines (PCVs) have successfully reduced rates of vaccine-type invasive disease and colonization both via direct effects in immunized children and, in some settings, indirect effects in unimmunized individuals. Limitations of the current PCV approach include the emergence of non-vaccine serotypes contributing to carriage and invasive disease in high-PCV coverage settings and the high cost of goods of PCVs which limits their accessibility in developing countries where the burden of disease remains highest. Furthermore, the distribution of serotypes causing disease varies geographically and includes more serotypes than are currently covered in a single PCV formulation. Researchers have long been exploring the potential of genetically conserved non-capsular pneumococcal antigens as vaccine candidates that might overcome such limitations. To better evaluate the rationale of such approaches, an understanding of the mechanisms of immunity to the various phases of pneumococcal infection is of paramount importance. Herein we will review the evolving understanding of both vaccine-induced and naturally acquired immunity to pneumococcal colonization and infection and discuss how this informs current approaches using serotype-independent pneumococcal vaccine candidates. We will then review the alternative vaccine candidates that have been or are currently under evaluation in clinical trials.

Trivalent pneumococcal protein vaccine protects against experimental acute otitis media caused by Streptococcus pneumoniae in an infant murine model

BACKGROUND

Currently licensed serotype-based pneumococcal vaccines are effective in preventing invasive pneumococcal diseases, but less effective in preventing non-bacteremic pneumonia and acute otitis media (AOM). We previously reported that a trivalent pneumococcal protein recombinant vaccine (PPrV) protected against pneumonia in a murine model. Here we evaluated PPrV protection against AOM in an infant murine model.

METHODS

C57BL/6J mice were intramuscularly vaccinated at 1-3weeks of age with monovalent pneumococcal histidine triad protein D (PhtD), or pneumococcal choline binding protein A (PcpA), or detoxified pneumolysin (PlyD1), or trivalent vaccine, and transtympanically challenged at 7-8weeks of age with 1×10²CFU of pneumococcal strain BG7322 (6A) or 1×10⁴CFU of pneumococcal nontypeable strain 0702064MEF. Serum IgG titers were determined by ELISA. At 24 and 48h post infection (hpi), animals were sacrificed and middle ear fluid (MEF) samples were collected to determine pneumococcal CFUs.

RESULTS

We found that vaccination of infant mice with monovalent and trivalent pneumococcal proteins elicited significant serum IgG antibody responses to corresponding component proteins. Vaccination with PhtD reduced BG7322 bacterial burdens in MEF at both 24 (p=0.05) and 48hpi (p=0.16). Vaccination with PcpA significantly reduced the bacterial burdens in MEF at both 24 (p=0.02) and 48hpi (p=0.004), and PlyD1 significantly reduced bacterial burden in MEF at 48hpi (p=0.02). Vaccination with trivalent PPrV (PhtD, PcpA and PlyD1) significantly reduced Spn burdens in MEF at both 24 (p=0.001) and 48hpi (p<0.0001). Similar reductions of bacterial burdens were found when the vaccinated animals were challenged with a non-typeable Spn strain. Vaccinated mice had significantly milder inflammatory cytokine levels (IL-1β, IL-6, TNF-α, MIP-2 and KC) in middle ears at 24hpi (all p values<0.05).

CONCLUSION

Trivalent PPrV confers protection against pneumococcal AOM in an infant murine model.

The Two-Component System ArlRS and Alterations in Metabolism Enable Staphylococcus aureus to Resist Calprotectin-Induced Manganese Starvation

During infection the host imposes manganese and zinc starvation on invading pathogens. Despite this, Staphylococcus aureus and other successful pathogens remain capable of causing devastating disease. However, how these invaders adapt to host-imposed metal starvation and overcome nutritional immunity remains unknown. We report that ArlRS, a global staphylococcal virulence regulator, enhances the ability of S. aureus to grow in the presence of the manganese-and zinc-binding innate immune effector calprotectin. Utilization of calprotectin variants with altered metal binding properties revealed that strains lacking ArlRS are specifically more sensitive to manganese starvation. Loss of ArlRS did not alter the expression of manganese importers or prevent S. aureus from acquiring metals. It did, however, alter staphylococcal metabolism and impair the ability of S. aureus to grow on amino acids. Further studies suggested that relative to consuming glucose, the preferred carbon source of S. aureus, utilizing amino acids reduced the cellular demand for manganese. When forced to use glucose as the sole carbon source S. aureus became more sensitive to calprotectin compared to when amino acids are provided. Infection experiments utilizing wild type and calprotectin-deficient mice, which have defects in manganese sequestration, revealed that ArlRS is important for disease when manganese availability is restricted but not when this essential nutrient is freely available. In total, these results indicate that altering cellular metabolism contributes to the ability of pathogens to resist manganese starvation and that ArlRS enables S. aureus to overcome nutritional immunity by facilitating this adaptation.

The ubiquitous pathogen Staphylococcus aureus is a serious threat to human health due to the continued spread of antibiotic resistance. This spread has made it challenging to treat staphylococcal infections and led to the call for new approaches to treat this devastating pathogen. One approach is to disrupt the ability of S. aureus to adapt to nutrient availability during infection. During infection, the host imposes manganese and zinc starvation on invading pathogens. However, the mechanisms utilized by Staphylococcus aureus to overcome this host defense are unknown. We report that ArlRS, a global staphylococcal virulence regulator, is important for resisting manganese starvation during infection. Loss of ArlRS does not prevent S. aureus from acquiring metals but instead renders the bacterium incapable of adapting to limited manganese availability. ArlRS mutants also have metabolic defects and a reduced ability to grow on amino acids. When using glucose as a carbon source S. aureus is more sensitive to manganese starvation and increases the expression of manganese transporters relative to when amino acids are provided suggesting a higher demand for manganese. These observations indicate that ArlRS contributes to resisting nutritional immunity by altering metabolism to reduce the staphylococcal demand for manganese.

Strategies to develop vaccines of pediatric interest

INTRODUCTION

The success of the vaccines available on the market has significantly increased interest in vaccine development. Areas covered: The main aim of this paper is to discuss the most important vaccines of pediatric interest that are currently being developed. New pneumococcal vaccines and vaccines against group B Streptococcus, Staphylococcus aureus and respiratory syncytial virus are analyzed in detail. Expert commentary: Advances in understanding human immunology, including human monoclonal antibody identification, sequencing technology, and the ability to solve atomic level structures of vaccine targets have provided tools to guide the rational design of future vaccines. It is likely that some of these vaccines will reach the market in the future and will thus partially contribute to the prevention of very severe diseases that significantly affect the morbidity and mortality of children. However, further studies in animals and several clinical trials in children must be performed before new vaccines become licensed.

Vaccination for the control of childhood bacterial pneumonia - Haemophilus influenzae type b and pneumococcal vaccines

Pneumonia in childhood is endemic in large parts of the world and in particular, in developing countries, as well as in many indigenous communities within developed nations. Haemophilus influenzae type b and Streptococcus pneumoniae conjugate vaccines are currently available against the leading bacterial causes of pneumonia. The use of the vaccines in both industrialised and developing countries have shown a dramatic reduction in the burden of pneumonia and invasive disease in children. However, the greatest threat facing pneumococcal conjugate vaccine effectiveness is serotype replacement. The current vaccines provide serotype-specific, antibody-mediated protection against only a few of the 90+ capsule serotypes. Therefore, there has been a focus in recent years to rapidly advance technologies that will result in broader disease coverage and more affordable vaccines that can be used in developing countries. The next generation of pneumococcal vaccines have advanced to clinical trials.

Effect of Pneumococcal Conjugate Vaccine on the Natural Antibodies and Antibody Responses Against Protein Antigens From Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis in Children With Community-acquired Pneumonia

BACKGROUND

Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis are common causative agents of respiratory infections. Pneumococcal conjugate vaccines have been introduced recently, but their effect on the natural immunity against protein antigens from these pathogens has not been elucidated.

METHODS

This was an age-matched observational controlled study that evaluated the influence of 10-valent pneumococcal conjugate vaccines on the levels of antibodies and frequencies of antibody responses against proteins from S. pneumoniae, H. influenzae and M. catarrhalis in serum samples of children with community-acquired pneumonia. Eight pneumococcal proteins (pneumolysin, choline-binding protein A, pneumococcal surface protein A families 1 and 2, pneumococcal choline-binding protein A, pneumococcal histidine triad protein D, serine/threonine protein kinase, protein required for cell wall separation of group B streptococcus), 3 proteins from H. influenzae (including protein D) and 5 M. catarrhalis proteins were investigated.

RESULTS

The study group comprised 38 vaccinated children and 114 age-matched controls (median age: 14.5 vs. 14.6 months, respectively; P = 0.997), all with community-acquired pneumonia. There was no difference on clinical baseline characteristics between vaccinated and unvaccinated children. Vaccinated children had significantly lower levels of antibodies against 4 of the studied pneumococcal antigens (P = 0.048 for Ply, P = 0.018 for pneumococcal surface protein A, P = 0.001 for StkP and P = 0.028 for PcsB) and higher levels of antibodies against M. catarrhalis (P = 0.015). Nevertheless, the vaccination status did not significantly affect the rates of antibody responses against S. pneumoniae, H. influenzae and M. catarrhalis.

CONCLUSIONS

In spite of the differences that have been found on the level of natural antibodies, no effect from pneumococcal vaccination was observed on the rate of immune responses associated with community-acquired pneumonia against protein antigens from S. pneumoniae, H. influenzae and M. catarrhalis.

Streptococcus pneumoniae fructose-1,6-bisphosphate aldolase, a protein vaccine candidate, elicits Th1/Th2/Th17-type cytokine responses in mice

Streptococcus pneumoniae (S. pneumoniae) is a major pathogen worldwide. The currently available polysaccharide-based vaccines significantly reduce morbidity and mortality. However, the inherent disadvantages of the currently available polysaccharide-based vaccines have motivated the search for other bacterial immunogens capable of eliciting a protective immune response against S. pneumoniae. Fructose-1,6-bisphosphate aldolase (FBA) is a glycolytic enzyme, which was found to localize to the bacterial surface, where it functions as an adhesin. Previously, immunizing mice with recombinant FBA (rFBA) in the presence of alum elicited a protective immune response against a lethal challenge with S. pneumoniae. Thus, the aim of the present study was to determine the cytokine responses that are indicative of protective immunity following immunization with rFBA. The protective effects against pneumococcal challenge in mice immunized with rFBA with complete Freund's adjuvant (CFA) in the initial immunization and with incomplete Freund's adjuvant (IFA) in booster immunizations surpassed the protective effects observed following immunization with either rFBA + alum or pVACfba. CD4+ T-cells obtained from the rFBA/CFA/IFA/IFA-immunized mice co-cultured with rFBA-pulsed antigen-presenting cells (APCs), exhibited a significantly greater proliferative ability than CD4+ T-cells obtained from the adjuvant-immunized mice co-cultured with rFBA‑pulsed APCs. The levels of the Th1-type cytokines, interferon (IFN)-γ, interleukin (IL)-2, tumor necrosis factor (TNF)-α and IL-12, the Th2-type cytokines, IL-4, IL-5 and IL-10, and the Th17-type cytokine, IL-17A, significantly increased within 72 h of the initiation of co-culture with CD4+ T-cells obtained from the rFBA‑immunized mice, in comparison with the co-cultures with CD4+ T-cells obtained from the adjuvant-immunized mice. Immunizing mice with rFBA resulted in an IgG1/IgG2 ratio of 41, indicating a Th2 response with substantial Th1 involvement. In addition, rabbit and mouse anti-rFBA antisera significantly protected the mice against a lethal S. pneumoniae challenge in comparison with preimmune sera. Our results emphasize the mixed involvement of the Th1, Th2 and Th17 arms of the immune system in response to immunization with pneumococcal rFBA, a potential vaccine candidate.

PcpA Promotes Higher Levels of Infection and Modulates Recruitment of Myeloid-Derived Suppressor Cells during Pneumococcal Pneumonia

We used two different infection models to investigate the kinetics of the PcpA-dependent pneumococcal disease in mice. In a bacteremic pneumonia model, we observed a PcpA-dependent increase in bacterial burden in the lungs, blood, liver, bronchoalveolar lavage, and spleens of mice at 24 h postinfection. This PcpA-dependent effect on bacterial burden appeared earlier (within 12 h) in the focal pneumonia model, which lacks bacteremia or sepsis. Histological changes show that the ability of pneumococci to make PcpA was associated with unresolved inflammation in both models of infection. Using our bacteremic pneumonia model we further investigated the effects of PcpA on recruitment of innate immune regulatory cells. The presence of PcpA was associated with increased IL-6 levels, suppressed production of TRAIL, and reduced infiltration of polymorphonuclear cells. The ability of pneumococci to make PcpA negatively modulated both the infiltration and apoptosis of macrophages and the recruitment of myeloid-derived suppressor-like cells. The latter have been shown to facilitate the clearance and control of bacterial pneumonia. Taken together, the ability to make PcpA was strongly associated with increased bacterial burden, inflammation, and negative regulation of innate immune cell recruitment to the lung tissue during bacteremic pneumonia.

Otitis-prone Children Have Immunologic Deficiencies in Naturally Acquired Nasopharyngeal Mucosal Antibody Response after Streptococcus pneumoniae Colonization

OBJECTIVES

Acute otitis media (AOM) is the most common pediatric bacterial infection, and stringently defined otitis-prone (sOP) children have immunologic deficiencies. We recently found that nasopharyngeal (NP) colonization by Streptococcus pneumoniae (Spn) elicits a NP mucosal antibody response to vaccine candidate pneumococcal proteins that correlate with protection from AOM in non-sOP (NOP) children. Here, we sought to determine if sOP children experience significantly higher colonization rates with Spn than NOP children, develop lower naturally acquired NP mucosal antibody responses to those same pneumococcal proteins after colonization by Spn, and suffer greater frequency of AOM as a consequence.

METHODS

NP samples were collected from 130 NOP and 45 sOP children during 270 healthy visits and 201 AOM visits between 6 and 24 months of age. Spn were identified by standard culture. NP mucosal IgG and IgA levels to vaccine candidate proteins pneumococcal histidine triad protein D, pneumococcal choline binding protein A (PcpA) and pneumolysin D1 were measured by quantitative enzyme-linked immunosorbent assay.

RESULTS

sOP children had significantly higher colonization frequency by Spn (P < 0.0001) and significantly lower IgG and IgA levels to all 3 vaccine candidate proteins studied compared with NOP children (all P values <0.05) except IgG to Ply D1 (P = 0.31). Spn colonization in NOP children led to 2-fold to 5-fold increase in mucosal IgG and IgA levels to all 3 proteins (all P values <0.01), whereas Spn colonization in sOP children generally failed to elicit antibody responses (all P values >0.05). PcpA was unique in inducing significant increases in mucosal IgA (P = 0.02). When high mucosal IgG levels to all 3 proteins and IgA to PcpA were measured, they correlated with reduced AOM in sOP children.

CONCLUSION

sOP children experience significantly higher colonization rates with Spn, develop lower naturally acquired NP mucosal antibody responses to pneumococcal vaccine candidate proteins pneumococcal histidine triad protein D, PcpA and pneumolysin D1 after colonization by Spn, and suffer greater frequency of AOM if they do not generate high mucosal antibody to the studied proteins.

Synchrony in serum antibody response to conserved proteins of Streptococcus pneumoniae in young children

Conserved Streptococcus pneumoniae (Spn) proteins are currently under investigation as vaccine candidates. We recently identified a subset of children prone to frequent acute otitis media (AOM) that we refer to as stringently-defined otitis prone (sOP). We investigated the synchrony of serum antibody responses against 5 Spn protein vaccine antigens, PhtD, LytB, PcpA, PhtE, and PlyD1 resulting from nasopharyngeal colonization and AOM in sOP children (49 observations) and non-otitis prone (NOP) children (771 observations). Changes in serum IgG and IgM were quantitated with ELISA. IgG antibody concentrations against PhtD, PcpA, and PlyD1 rose in synchrony in sOP and NOP children; that is, the proteins appeared equally and highly immunogenic in children at age 6 to 15 months and then leveled off in their rise at 15 to 25 months. In contrast, rises in concentrations to PhtE and LytB were significantly slower and had not peaked in children even at 25 months of age, consistent with lower immunogenicity. Serum IgM responses against PhtD and PlyD1 were in synchrony in children at age 6-25 months old. PcpA did not induce a significant increase of serum IgM response in children, suggesting that primary responses to PcpA occurred prior to children attaining age 6 months old. PhtD, PcpA, and Ply elicit a synchronous natural acquisition of serum antibody in young children suggesting that a trivalent Spn protein vaccine combining PhtD, PcpA, and PlyD1 would be less likely to display antigen competition when administered as a combination vaccine in young children.

The host immune dynamics of pneumococcal colonization: implications for novel vaccine development

The human nasopharynx (NP) microbiota is complex and diverse and Streptococcus pneumoniae (pneumococcus) is a frequent member. In the first few years of life, children experience maturation of their immune system thereby conferring homeostatic balance in which pneumococci are typically rendered as harmless colonizers in the upper respiratory environment. Pneumococcal carriage declines in many children before they acquire capsular-specific antibodies, suggesting a capsule antibody-independent mechanism of natural protection against pneumococcal carriage in early childhood. A child's immune system in the first few years of life is Th2-skewed so as to avoid inflammation-induced immunopathology. Understanding Th1/Th2 and Th17 ontogeny in early life and how adjuvant vaccine formulations shift the balance of T helper-cell differentiation, may facilitate the development of new protein-based pneumococcal vaccines. This article will discuss the immune dynamics of pneumococcal colonization in infants. The discussion aims to benefit the design and improvement of protein subunit-based next-generation pneumococcal vaccines.

Transcriptional and metabolic effects of glucose on Streptococcus pneumoniae sugar metabolism

Streptococcus pneumoniae is a strictly fermentative human pathogen that relies on carbohydrate metabolism to generate energy for growth. The nasopharynx colonized by the bacterium is poor in free sugars, but mucosa lining glycans can provide a source of sugar. In blood and inflamed tissues glucose is the prevailing sugar. As a result during progression from colonization to disease S. pneumoniae has to cope with a pronounced shift in carbohydrate nature and availability. Thus, we set out to assess the pneumococcal response to sugars found in glycans and the influence of glucose (Glc) on this response at the transcriptional, physiological, and metabolic levels. Galactose (Gal), N-acetylglucosamine (GlcNAc), and mannose (Man) affected the expression of 8 to 14% of the genes covering cellular functions including central carbon metabolism and virulence. The pattern of end-products as monitored by in vivo¹³C-NMR is in good agreement with the fermentation profiles during growth, while the pools of phosphorylated metabolites are consistent with the type of fermentation observed (homolactic vs. mixed) and regulation at the metabolic level. Furthermore, the accumulation of α-Gal6P and Man6P indicate metabolic bottlenecks in the metabolism of Gal and Man, respectively. Glc added to cells actively metabolizing other sugar(s) was readily consumed and elicited a metabolic shift toward a homolactic profile. The transcriptional response to Glc was large (over 5% of the genome). In central carbon metabolism (most represented category), Glc exerted mostly negative regulation. The smallest response to Glc was observed on a sugar mix, suggesting that exposure to varied sugars improves the fitness of S. pneumoniae. The expression of virulence factors was negatively controlled by Glc in a sugar-dependent manner. Overall, our results shed new light on the link between carbohydrate metabolism, adaptation to host niches and virulence.

Poor memory B cell generation contributes to non-protective responses to DTaP vaccine antigens in otitis-prone children

We recently identified a cohort of children with recurrent episodes of acute otitis media (AOM) who fail to generate protective antibody titres to otopathogens and several vaccine antigens. In this study we determined the antibody levels against DTaP vaccine antigens, diphtheria toxoid (DT), tetanus toxoid (TT) and acellular pertussis toxoid (PT) in sera from 15 stringently defined otitis-prone (sOP) children and 20 non-otitis-prone (NOP) children. We found significantly lower concentrations of immunoglobulin (Ig)G antibodies against vaccine antigens in the serum of sOP children compared to age-matched NOP children. To elucidate immunological cellular responses to the vaccines in these children, we investigated memory B cell responses to DTaP vaccination. We used fluorescently conjugated vaccine antigens to label antigen receptors on the surface of memory B cells and examined the frequency of antigen-specific CD19(+) CD27(+) memory B cells in the peripheral blood. sOP children showed a significantly lower percentage of antigen-specific CD19(+) CD27(+) memory B cells than NOP children. We also found a linear correlation between the frequencies of memory B cells and circulating IgG titres for DT, TT and PT proteins. To our knowledge, this is the first study to show significant differences in memory B cell responses to DTaP vaccine antigens and their correlation with the circulating antibodies in young children with recurrent AOM.

Higher levels of mucosal antibody to pneumococcal vaccine candidate proteins are associated with reduced acute otitis media caused by Streptococcus pneumoniae in young children

Mucosal immunity has a crucial role in controlling human respiratory tract infections. This study characterizes the naturally acquired mucosal antibody levels to three Streptococcus pneumoniae (Spn) protein antigens, pneumococcal histidine triad protein D (PhtD), pneumococcal choline binding protein A (PcpA), and pneumolysin (Ply), and assesses the association of the mucosal antibody levels with occurrence of acute otitis media (AOM) caused by Spn. Both nasopharyngeal (NP) immunoglobulin G (IgG) and IgA levels to all three proteins slightly decreased in children from 6 to 9 months of age and then gradually increased through 24 months of age. Spn NP colonization was associated with higher mucosal antibody levels to all three proteins. However, children with Spn AOM had 5-8-fold lower IgG and 3-6-fold lower IgA levels to the three proteins than children without AOM but asymptomatically colonized with Spn. Antigen-specific antibody levels in the middle ear fluid (MEF) were correlated with antibody levels in the NP. Children with AOM caused by Spn had lower antibody levels in both the MEF and NP than children with AOM caused by other pathogens. These results indicate that higher naturally acquired mucosal antibody levels to PhtD, PcpA and Ply are associated with reduced AOM caused by Spn.

Trivalent pneumococcal protein recombinant vaccine protects against lethal Streptococcus pneumoniae pneumonia and correlates with phagocytosis by neutrophils during early pathogenesis

OBJECTIVE

Due to the fact that current polysaccharide-based pneumococcal vaccines have limited serotype coverage, protein-based vaccine candidates have been sought for over a decade to replace or complement current vaccines. We previously reported that a trivalent Pneumococcal Protein recombinant Vaccine (PPrV), showed protection against pneumonia and sepsis in an infant murine model. Here we investigated immunological correlates of protection of PPrV in the same model.

METHODS

C57BL/6J infant mice were intramuscularly vaccinated at age 1-3 weeks with 3 doses of PPrV, containing pneumococcal histidine triad protein D (PhtD), pneumococcal choline binding protein A (PcpA), and detoxified pneumolysin mutant PlyD1. 3-4 weeks after last vaccination, serum and lung antibody levels to PPrV components were measured, and mice were intranasally challenged with a lethal dose of Streptococcus pneumoniae (Spn) serotype 6A. Lung Spn bacterial burden, number of neutrophils and alveolar macrophages, phagocytosed Spn by granulocytes, and levels of cytokines and chemokines were determined at 6, 12, 24, and 48h after challenge.

RESULTS

PPrV vaccination conferred 83% protection against Spn challenge. Vaccinated mice had significantly elevated serum and lung antibody levels to three PPrV components. In the first stage of pathogenesis of Spn induced pneumonia (6-24h after challenge), vaccinated mice had lower Spn bacterial lung burdens and more phagocytosed Spn in the granulocytes. PPrV vaccination led to lower levels of pro-inflammatory cytokines IL-6, IL-1β, and TFN-α, and other cytokines and chemokines (IL-12, IL-17, IFN-γ, MIP-1b, MIP-2 and KC, and G-CSF), presumably due to a lower lung bacterial burden.

CONCLUSION

Trivalent PPrV vaccination results in increased serum and lung antibody levels to the vaccine components, a reduction in Spn induced lethality, enhanced early clearance of Spn in lungs due to more rapid and thorough phagocytosis of Spn by neutrophils, and correspondingly a reduction in lung inflammation and tissue damage.

Human antibodies to PhtD, PcpA, and Ply reduce adherence to human lung epithelial cells and murine nasopharyngeal colonization by Streptococcus pneumoniae

Streptococcus pneumoniae adherence to human epithelial cells (HECs) is the first step in pathogenesis leading to infections. We sought to determine the role of human antibodies against S. pneumoniae protein vaccine candidates PhtD, PcpA, and Ply in preventing adherence to lung HECs in vitro and mouse nasopharyngeal (NP) colonization in vivo. Human anti-PhtD, -PcpA, and -Ply antibodies were purified and Fab fragments generated. Fabs were used to test inhibition of adherence of TIGR4 and nonencapsulated strain RX1 to A549 lung HECs. The roles of individual proteins in adherence were tested using isogenic mutants of strain TIGR4. Anti-PhtD, -PcpA, and -Ply human antibodies were assessed for their ability to inhibit NP colonization in vivo by passive transfer of human antibody in a murine model. Human antibodies generated against PhtD and PcpA caused a decrease in adherence to A549 cells (P < 0.05). Anti-PhtD but not anti-PcpA antibodies showed a protective role against mouse NP colonization. To our surprise, anti-Ply antibodies also caused a significant (P < 0.05) reduction in S. pneumoniae colonization. Our results support the potential of PhtD, PcpA, and Ply protein vaccine candidates as alternatives to conjugate vaccines to prevent non-serotype-specific S. pneumoniae colonization and invasive infection.

Vaccination with a Streptococcus pneumoniae trivalent recombinant PcpA, PhtD and PlyD1 protein vaccine candidate protects against lethal pneumonia in an infant murine model

Streptococcus pneumoniae infections continue to cause significant worldwide morbidity and mortality despite the availability of efficacious serotype-dependent vaccines. The need to incorporate emergent strains expressing additional serotypes into pneumococcal polysaccharide conjugate vaccines has led to an identified need for a pneumococcal protein-based vaccine effective against a broad scope of serotypes. A vaccine consisting of several conserved proteins with different functions during pathogenesis would be preferred. Here, we investigated the efficacy of a trivalent recombinant protein vaccine containing pneumococcal choline-binding protein A (PcpA), pneumococcal histidine triad D (PhtD), and genetically detoxified pneumolysin (PlyD1) in an infant mouse model. We found the trivalent vaccine conferred protection from lethal pneumonia challenges using serotypes 6A and 3. The observed protection with trivalent PcpA, PhtD, and PlyD1 vaccine in infant mice supports the ongoing study of this candidate vaccine in human infant clinical trials.

A fluorescent multiplexed bead-based immunoassay (FMIA) for quantitation of IgG against Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis protein antigens

Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis are pathogens commonly associated with infectious diseases in childhood. This study aimed to develop a fluorescent multiplexed bead-based immunoassay (FMIA) using recombinant proteins for the quantitation of serum IgG antibodies against these bacteria. Eight pneumococcal proteins (Ply, CbpA, PspA1, PspA2, PcpA, PhtD, SP1732-3 and SP2216-1), 3 proteins of H. influenzae (NTHi Protein D, NTHi0371-1, NTHi0830), and 5 proteins of M. catarrhalis (MC Omp CD, MC_RH4_2506, MC_RH4_1701, MC_RH4_3729-1, MC_RH4_4730) were used to develop the FMIA. Optimal coupling concentrations for each protein, comparison of singleplex and multiplex assays, specificity, reproducibility, and correlation to ELISA for six pneumococcal antigens were determined for validation. FMIA was then used to analyze acute and convalescent paired serum samples of 50 children with non-severe pneumonia. The coupling concentrations varied for different antigens, ranging from 1.6 to 32μg of protein/million beads. Correlation between singleplexed and multiplexed assays was excellent, with R≥0.987. The FMIA was specific, reaching >92% homologous inhibition for all specificities; heterologous inhibition ≥20% was found only in six cases. The assay was repeatable, with averages of intra-assay variation ≤10.5%, day-to-day variation ≤9.7% and variation between technicians ≤9.1%. Comparison with ELISA for pneumococcal antigens demonstrated good correlation with R ranging from 0.854 (PspA2) to 0.976 (PcpA). The samples from children showed a wide range of antibody concentrations and increases in convalescent samples. In conclusion, the FMIA was sensitive, specific, and repeatable, using small amounts of recombinant proteins and sera to detect antibodies against S. pneumoniae, H. influenzae and M. catarrhalis. The methodology would be suitable for studies investigating etiological diagnosis and in experimental vaccine studies.

Role of Pht proteins in attachment of Streptococcus pneumoniae to respiratory epithelial cells

Pneumococcal adherence to mucosal surfaces is a critical step in nasopharyngeal colonization, but so far few pneumococcal adhesins involved in the interaction with host cells have been identified. PhtA, PhtB, PhtD, and PhtE are conserved pneumococcal surface proteins that have proven promising as vaccine candidates. One suggested virulence function of Pht proteins is to mediate adherence at the respiratory mucosa. In this study, we assessed the role of Pht proteins in pneumococcal binding to respiratory epithelial cells. Pneumococci were incubated with human nasopharyngeal epithelial cells (Detroit-562) and lung epithelial cells (A549 and NCI-H292), and the proportion of bound bacteria was measured by plating viable counts. Strains R36A (unencapsulated), D39 (serotype 2), 43 (serotype 3), 4-CDC (serotype 4), and 2737 (serotype 19F) with one or more of the four homologous Pht proteins deleted were compared with their wild-type counterparts. Also, the effect of anti-PhtD antibodies on the adherence of strain 2737 to the respiratory epithelial cells was studied. Our results suggest that Pht proteins play a role in pneumococcal adhesion to the respiratory epithelium. We also found that antibody to PhtD is able to inhibit bacterial attachment to the cells, suggesting that antibodies against PhtD present at mucosal surfaces might protect from pneumococcal attachment and subsequent colonization. However, the relative significance of Pht proteins to the ability of pneumococci to bind in vitro to epithelial cells depends on the genetic background and the capsular serotype of the strain.

Safety and immunogenicity of pneumococcal protein vaccine candidates: monovalent choline-binding protein A (PcpA) vaccine and bivalent PcpA-pneumococcal histidine triad protein D vaccine

BACKGROUND

Pneumococcal vaccines based on protein antigens may provide expanded protection against Streptococcus pneumoniae.

OBJECTIVE

To evaluate safety and immunogenicity in adults of pneumococcal vaccine candidates comprising S. pneumoniae pneumococcal histidine triad protein D (PhtD) and pneumococcal choline-binding protein A (PcpA) in monovalent and bivalent formulations.

METHODS

This was a phase I, randomized, observer-blinded, placebo-controlled, step-wise dose-escalation study. Following a pilot safety study in which participants received one intramuscular injection of either aluminum hydroxide (AH)-adjuvanted PcpA (25 μg) or PhtD-PcpA (10 μg each), participants in the main study received AH-adjuvanted PcpA (25 μg), AH-adjuvanted PhtD-PcpA (10, 25, or 50 μg each), unadjuvanted PhtD-PcpA (25 μg each), or placebo as 2 injections 30 days apart. Assignment of successive dose cohorts was made after blinded safety reviews after each dose level. Safety endpoints included rates of solicited injection site and systemic reactions, unsolicited adverse events (AEs), serious AEs (SAEs), and safety laboratory tests. Immunogenicity endpoints included levels of anti-PhtD and anti-PcpA antibodies (ELISA).

RESULTS

Six adults 18-50 years of age were included in the pilot study and 125 in the main study. No obvious increases in solicited reactions or unsolicited AEs were reported with escalating doses (adjuvanted vaccine) after either injection, or with repeated administration. Adjuvanted vaccine candidates were associated with a higher incidence of solicited reactions (particularly injection site reactions) than unadjuvanted vaccine candidates. However, no SAE or discontinuation due to an AE occurred. Geometric mean concentrations of anti-PhtD IgG and anti-PcpA IgG increased significantly after injection 2 compared with injection 1 at each dose level. No enhancement of immune responses was shown with adjuvanted vaccine candidates compared with the unadjuvanted vaccine candidate. In the dose-escalating comparison, a plateau effect at the 25 μg dose was observed as measured by geometric mean concentrations and by fold increases.

CONCLUSIONS

Promising safety profiles and immunogenicity of these monovalent and bivalent protein vaccine candidates were demonstrated in an adult population (ClinicalTrials.gov registry no. NCT01444339).

Antibody response to Streptococcus pneumoniae proteins PhtD, LytB, PcpA, PhtE and Ply after nasopharyngeal colonization and acute otitis media in children

We prospectively compared serum antibody levels of 5 Streptococcus pneumoniae (Spn) proteins: PcpA PhtD, PhtE Ply and LytB associated with nasopharyngeal (NP) colonization and acute otitis media (AOM) infection in a cohort of 6-30 mo old children. Antigen-specific antibody titers were determined by ELISA. A total of 731 visits among 168 children were studied. There were 301 Spn NP colonization episodes documented in 109 (65%) children and 42 Spn AOM episodes in 34 (20%) children. IgG antibody titers to the 5 proteins were significantly different among children over time (p < 0.001), with a rank order as follows: PcpA > PhtE = PhtD > Ply > LytB Characterization of IgG and IgM acute and convalescent serum antibody levels of Spn AOM infection showed the kinetics of the response differed among children, with the same rank order of antibody levels over time. Individual data showed that some children responded to AOM with an antibody increase to one or more of these Spn proteins but some children failed to respond. We conclude that antibody levels to Spn proteins PcpA PhtD, PhtE, Ply and LytB, all rise over time in children age 6 to 30 mo following natural exposure to Spn after NP colonization and AOM; however, there were significant differences in quantity of antibody elicited among these potential vaccine antigens.