Protection against pneumococcal pneumonia in mice by monoclonal antibodies to pneumolysin

Antibody cocktails: next-generation biopharmaceuticals with improved potency

The therapeutic and commercial success of monoclonal antibodies (mAbs) has inspired innovative approaches aimed at increasing their potency and broadening their applicability. Among these, cocktails of recombinant human mAbs are a logical next step because they combine the technological advances made in the field of antibody engineering with the notion that the ingredients of polyclonal-antibody preparations act in concert to optimally exert and recruit effector functions. Cocktails of mAbs have entered clinical trials, and new technology platforms are being developed for their generation. On the basis of preclinical and early clinical results, the question is not whether cocktails of mAbs have a bright future as therapeutics, but rather what platform is able to reproducibly and cost effectively generate efficacious concoctions that are approvable by the regulatory authorities.

Enhanced protection against pneumococcal infection elicited by immunization with the combination of PspA, PspC, and ClpP

Immunization with a combination of several virulence-associated proteins is one of the strategies of developing effective protein-based vaccines to enhance the protection against Streptococcus pneumoniae. In this study, we evaluated the protection effects against pneumococcal infection caused by S. pneumoniae TIGR4 in BALB/c mice immunized with either single pneumococcal surface protein A (PspA), pneumococcal surface protein C (PspC), the caseinolytic protease (ClpP) or their combinations. The median survival times for mice immunized with single antigen or their combinations were significantly longer than that for mice treated with adjuvant alone. Mice treated with a combination of three antigens survived significantly longer than those that received either single or two antigens. The highest survival rate of the various groups of mice was observed with the combination of three antigens, this survival rate was significantly different from those for mice that received either single antigen or the combinations of two antigens except the mixture of ClpP and PspA. In the experiment of passive immunization with hyperimmune serums containing their specific polyclonal antibodies (anti-PspA serum, anti-PspC serum, anti-ClpP serum), the median survival times for mice immunized with hyperimmune serums containing specific polyclonal antibodies were significantly longer than that for control mice, the treatment of serum containing only one single polyclonal antibody could not provide higher survival rate than control serum. However, the survival rates for mice treated with the serums containing combined polyclonal antibodies were significantly higher than those for mice treated with either control serum or anti-PspA serum alone. Immunization with the combination of three hyperimmune serums also provided the best protection against S. pneumoniae. Compared to mice treated with serum containing single polyclonal antibody, the survival rate for mice treated with serums containing three polyclonal antibodies was significantly higher but was not different from those for mice treated with serums containing two polyclonal antibodies. Our findings provided evidence that a mixture of PspA, PspC, and ClpP or their polyclonal antibodies could enhance the protection against pneumococcal infection acting a synergetic effect.

Streptococcus pneumoniae virulence factors and their clinical impact: An update

The morbidity and mortality rates associated with Streptococcus pneumoniae remain very high worldwide. The virulence of this bacterium is largely dependent on its polysaccharide capsule, which is quite heterogeneous and represents a serious obstacle for designing effective vaccines. However, it has been demonstrated that numerous protein virulence factors are involved in the pathogenesis of pneumococcal disease. An important related finding from experimental animal models is that non-capsulated strains of pneumococci are protective against capsulated ones. Hence, new vaccine designs are focused on the surface proteins (e. g., PspA and PspC) and on the cytolysin, pneumolysin. Moreover, several virulence factors have potential value for pneumococcal diagnosis by urinalysis. In this paper, we review the virulence factors involved in bacteria-host interactions, and the new developments in vaccines and diagnostic methods.

Vaccines in the era of genomics: the pneumococcal challenge

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

The role of pneumolysin in mediating lung damage in a lethal pneumococcal pneumonia murine model

Background

Intranasal inoculation of Streptococcus pneumoniae D39 serotype 2 causes fatal pneumonia in mice. The cytotoxic and inflammatory properties of pneumolysin (PLY) have been implicated in the pathogenesis of pneumococcal pneumonia.

Methods

To examine the role of PLY in this experimental model we performed ELISA assays for PLY quantification. The distribution patterns of PLY and apoptosis were established by immunohistochemical detection of PLY, caspase-9 activity and TUNEL assay on tissue sections from mice lungs at various times, and the results were quantified with image analysis. Inflammatory and apoptotic cells were also quantified on lung tissue sections from antibody treated mice.

Results

In bronchoalveolar lavages (BAL), total PLY was found at sublytic concentrations which were located in alveolar macrophages and leukocytes. The bronchoalveolar epithelium was PLY-positive, while the vascular endothelium was not PLY reactive. The pattern and extension of cellular apoptosis was similar. Anti-PLY antibody treatment decreased the lung damage and the number of apoptotic and inflammatory cells in lung tissues.

Conclusion

The data strongly suggest that in vivo lung injury could be due to the pro-apoptotic and pro-inflammatory activity of PLY, rather than its cytotoxic activity. PLY at sublytic concentrations induces lethal inflammation in lung tissues and is involved in host cell apoptosis, whose effects are important to pathogen survival.

Targeting virulence for antibacterial chemotherapy: identifying and characterising virulence factors for lead discovery

The antibacterial drug discovery industry is fast losing participants; at the same time it is facing the challenge of developing new antibiotics that are effective against frequently occurring and multiply resistant organisms. One intriguing approach is to target bacterial virulence, and the last decade or so has seen a focus on bacterial pathogenesis along with the development of reagents and strategies that could make this possible. Several processes utilised by a range of bacteria to cause infection may be conserved enough to make attractive targets; indeed it is known that mammalian cells can affect bacterial gene expression and vice versa. Interesting targets involving virulence include type III secretion systems, two-component signal transduction systems, quorum sensing, and biofilm formation. In order to better understand these systems and strategies, investigators have developed novel strategies of their own, involving negative selections, surrogate models of infection, and screens for gene induction and antigenicity. Inhibitors of such targets would be unlikely to adversely affect patients, be cross-resistant to existing therapies, or cause resistance themselves. It might be the case that virulence target-based therapies would not be powerful enough to clear an existing infection alone, but if they are instead considered as adjunct therapy to existing antibiotics, or potentiators of the host immune response, they may show efficacy in a non-traditional way.

New perspectives for a new century: implications of pathogen responses for the future of antimicrobial therapy

Although the discovery of new classes of antibiotics has lagged behind in the last three decades, the incidence of life-threatening nosocomial infections that are resistant to multiple antibacterial agents has increased steadily. Recent advances in bacterial pathogenicity through the identification of a number of virulence factors and the bacterial genetics behind it have opened the way to a clearer understanding of the pathogen-host relationship. Bacteria communicate with each other through specific signaling chemicals to act as a community rather than individual cells to achieve a critical density or a "quorum." Establishment of quorum is the initiating signal for turning on a variety of virulence factors essential for the pathogenicity and dissemination of pathogens through the host. Pathogenic bacteria use a variety of biochemical mediators, collectively called "virulence factors," to invade and attack host tissues and to avoid detection and elimination by the host immune system. Delineating the specific responses the host immune system elicits in response to specific virulence factors and quorum-sensing molecules is essential to the development of new diagnostic methods for early detection of an infection and the prognosis to a given antibacterial therapy. Identification of inhibitors of virulence factors will represent new antimicrobial therapeutic modalities, and this can be used synergistically with current antibiotic therapy because they act through independent prokaryotic pathways to inhibit bacterial growth and survival.

Construction and immunological characterization of a novel nontoxic protective pneumolysin mutant for use in future pneumococcal vaccines

Pneumolysin, the pore-forming toxin produced by Streptococcus pneumoniae, may have an application as an immunogenic carrier protein in future pneumococcal conjugate vaccines. Most of the 90 S. pneumoniae serotypes identified produce pneumolysin; therefore, this protein may confer non-serotype-specific protection against pneumococcal infections such as pneumonia, meningitis, and otitis media. However, as pneumolysin is highly toxic, a nontoxic form of pneumolysin would be a more desirable starting point in terms of vaccine production. Previous pneumolysin mutants have reduced activity but retain residual toxicity. We have found a single amino acid deletion that blocks pore formation, resulting in a form of pneumolysin that is unable to form large oligomeric ring structures. This mutant is nontoxic at concentrations greater than 1,000 times that of the native toxin. We have demonstrated that this mutant is as immunogenic as native pneumolysin without the associated effects such as production of the inflammatory mediators interleukin-6 and cytokine-induced neutrophil chemoattractant KC, damage to lung integrity, and hypothermia in mice. Vaccination with this mutant protects mice from challenge with S. pneumoniae. Incorporation of this mutant pneumolysin into current pneumococcal vaccines may increase their efficacy.

Pneumolysin-mediated activation of NFkappaB in human neutrophils is antagonized by docosahexaenoic acid

This study was designed to investigate the relationship between influx of extracellular Ca(2+), activation of NFkappaB and synthesis of interleukin-8 (IL-8) following exposure of human neutrophils to subcytolytic concentrations (8.37 and 41.75 ng/ml) of the pneumococcal toxin, pneumolysin, as well as the potential of the omega-3 polyunsaturated fatty acid, docosahexaenoic acid, to antagonize these events. Activation and translocation of NFkappaB were measured using a radiometric electrophoretic mobility shift assay, while influx of extracellular Ca(2+) and synthesis of IL-8 were determined using a radioassay and an ELISA procedure, respectively. Exposure of neutrophils to pneumolysin was accompanied by influx of Ca(2+), activation of NFkappaB, and synthesis of IL-8, all of which were eliminated by inclusion of the Ca(2+)-chelating agent, EGTA (10 m m), in the cell-suspending medium, as well as by pretreatment of the cells with docosahexaenoic acid (5 and 10 microg/ml). The antagonistic effects of docosahexaenoic acid on these pro-inflammatory interactions of pneumolysin with neutrophils were not attributable to inactivation of the toxin, and required the continuous presence of the fatty acid. These observations demonstrate that activation of NFkappaB and synthesis of IL-8, following exposure of neutrophils to pneumolysin are dependent on toxin-mediated influx of Ca(2+) and that these potentially harmful activities of the toxin are antagonized by docosahexaenoic acid.

Application of Microbial Genomic Science to Advanced Therapeutics

Since the publication of the first complete microbial genome sequence of Haemophilus influenzae in 1995, more than 200 additional microbial genome sequences have become available in the public domain. Approximately 40% of these represent important human pathogens. Comparative in silico methods, along with large-scale approaches such as transcriptomics and proteomics, are beginning to reveal insights into new virulence genes, pathogen-host interactions, and the molecular basis of host specificity. Sequence data are also starting to accumulate from multiple isolates or strains of a single pathogen, and this type of data has proven to be quite valuable in providing new insights into the genetic variability that is present in a particular species as well as in facilitating correlations between genotype and phenotype. Ultimately, a major goal of genome-enabled infectious disease research is the development of novel diagnostics, therapeutics, and vaccines.