Development of a whole cell pneumococcal vaccine: BPL inactivation, cGMP production, and stability

Peptide linker increased the stability of pneumococcal fusion protein vaccine candidate

Streptococcus pneumoniae is a bacterial pathogen exclusive to humans, responsible for respiratory and systemic diseases. Pneumococcal protein vaccines have been proposed as serotype-independent alternatives to currently used conjugated polysaccharide vaccines, which have presented limitations regarding their coverage. Previously in our group, pneumococcal surface protein A (PspA) and detoxified pneumolysin (PdT) were genetically fused and the hybrid protein protected mice against pneumococcal challenge, offered higher cross-protection against different strains and showed greater opsonophagocytosis rate than co-administered proteins. As juxtaposed fusion was unstable to upscale production of the protein, flexible (PspA-FL-PdT) and rigid (PspA-RL-PdT) molecular linkers were inserted between the antigens to increase stability. This work aimed to produce recombinant fusion proteins, evaluate their stability after linker insertion, both in silico and experimentally, and enable the production of two antigens in a single process. The two constructs with linkers were cloned into Escherichia coli and hybrid proteins were purified using chromatography; purity was evaluated by SDS-PAGE and stability by Western blot and high performance size exclusion chromatography. PspA-FL-PdT showed higher stability at -20°C and 4°C, without additional preservatives. In silico analyses also showed differences regarding stability of the fusion proteins, with molecule without linker presenting disallowed amino acid positions in Ramachandran plot and PspA-FL-PdT showing the best scores, in agreement with experimental results. Mice were immunized with three doses and different amounts of each protein. Both fusion proteins protected all groups of mice against intranasal lethal challenge. The results show the importance of hybrid protein structure on the stability of the products, which is essential for a successful bioprocess development.

Acute otitis media pneumococcal disease burden and nasopharyngeal colonization in children due to serotypes included and not included in current and new pneumococcal conjugate vaccines

INTRODUCTION

Despite the introduction of effective pneumococcal conjugate vaccines (PCV), Streptococcus pneumoniae remains a major cause of acute otitis media (AOM) worldwide. New, higher valency vaccines that offer broader serotype coverage have been recently developed and others are in development. However, given the capsular serotypes expressed by pneumococci causing AOM, it is unclear to what extent differing or higher valency PCVs will provide additional protection.

AREAS COVERED

We conducted a systematic literature search of the MEDLINE database to identify articles published from January 2016 to September 2021 in 4 low and middle income and 10 high-income countries. We searched PubMed with terms: (Streptococcus pneumoniae) OR pneumococcal AND serotype AND (conjugate vaccine). We evaluated serotype distribution and the actual or projected coverage of pneumococcal serotypes by PCV10 (GlaxoSmithKline), PCV13 (Pfizer), PCV10SII (Serum Institute of India) PCV15 (Merck) and PCV20 (Pfizer).

EXPERT OPINION

Our review highlights the important epidemiological differences in serotype distribution and coverage by existing and higher valency vaccines to protect against AOM in children. These data provide support for further evaluation of serotype-independent vaccines for optimal control of pneumococcal AOM disease worldwide.

Production of inactivated gram-positive and gram-negative species with preserved cellular morphology and integrity

There are many approaches available to produce inactive bacteria by termination of growth, each with a different efficacy, impact on cell integrity, and potential for application in standardized inactivation protocols. The aim of this study was to compare these approaches and develop a standardized protocol for generation of inactivated Gram-positive and Gram-negative bacteria, yielding cells that are metabolically dead with retained cellular integrity i.e., preserving the surface and limited leakage of intracellular proteins and DNA. These inactivated bacteria are required for various applications, for instance, when investigating receptor-triggered signaling or bacterial contact-dependent analysis of cell lines requiring long incubation times. We inactivated eight different bacterial strains of different species by treatment with beta-propiolactone, ethanol, formalin, sodium hydroxide, and pasteurization. Inactivation efficacy was determined by culturing, and cell wall integrity assessed by quantifying released DNA, bacterial membrane and intracellular DNA staining, and visualization by scanning electron microscopy. Based on these results, we discuss the bacterial inactivation methods, and their advantages and disadvantages to study host-microbe interactions with inactivated bacteria.

Development of Next Generation Streptococcus pneumoniae Vaccines Conferring Broad Protection

Streptococcus pneumoniae is a major pathogen causing pneumonia with over 2 million deaths annually, especially in young children and the elderly. To date, at least 98 different pneumococcal capsular serotypes have been identified. Currently, the vaccines for prevention of S. pneumoniae infections are the 23-valent pneumococcal polysaccharide-based vaccine (PPV23) and the pneumococcal conjugate vaccines (PCV10 and PCV13). These vaccines only cover some pneumococcal serotypes and are unable to protect against non-vaccine serotypes and unencapsulated S. pneumoniae. This has led to a rapid increase in antibiotic-resistant non-vaccine serotypes. Hence, there is an urgent need to develop new, effective, and affordable pneumococcal vaccines, which could cover a wide range of serotypes. This review discusses the new approaches to develop effective vaccines with broad serotype coverage as well as recent development of promising pneumococcal vaccines in clinical trials. New vaccine candidates are the inactivated whole-cell vaccine strain (Δpep27ΔcomD mutant) constructed by mutations of specific genes and several protein-based S. pneumoniae vaccines using conserved pneumococcal antigens, such as lipoprotein and surface-exposed protein (PspA). Among the vaccines in Phase 3 clinical trials are the pneumococcal conjugate vaccines, PCV-15 (V114) and 20vPnC. The inactivated whole-cell and several protein-based vaccines are either in Phase 1 or 2 trials. Furthermore, the recent progress of nanoparticles that play important roles as delivery systems and adjuvants to improve the performance, as well as the immunogenicity of the nanovaccines, are reviewed.

Process intensification for production of Streptococcus pneumoniae whole-cell vaccine

The available pneumococcal conjugate vaccines provide protection against only those serotypes that are included in the vaccine, which leads to a selective pressure and serotype replacement in the population. An alternative low-cost, safe and serotype-independent vaccine was developed based on a nonencapsulated pneumococcus strain. This study evaluates process intensification to improve biomass production and shows for the first time the use of perfusion-batch with cell recycling for bacterial vaccine production. Batch, fed-batch, and perfusion-batch were performed at 10 L scale using a complex animal component-free culture medium. Cells were harvested at the highest optical density, concentrated and washed using microfiltration or centrifugation to compare cell separation methods. Higher biomass was achieved using perfusion-batch, which removes lactate while retaining cells. The biomass produced in perfusion-batch would represent at least a fourfold greater number of doses per cultivation than in the previously described batch process. Each strategy yielded similar vaccines in terms of quality as evaluated by western blot and animal immunization assays, indicating that so far, perfusion-batch is the best strategy for the intensification of pneumococcal whole-cell vaccine production, as it can be integrated to the cell separation process keeping the same vaccine quality.

The long search for a serotype independent pneumococcal vaccine

Introduction: Serotype replacement - a consequence of polysaccharide vaccine use - will continue to drive the inclusion of new serotypes on conjugate vaccines, increasing production complexity and costs, and making an already expensive vaccine less accessible to developing countries, where prevalence is higher and resources available for health systems, scarcer. Serotype-independent formulations are a promising option, but so far they have not been successful in reducing colonization/transmission.Areas covered: Protein-based and whole-cell vaccine candidates studied in the past 30 years. Challenges for serotype-independent vaccine development and alternative approaches.Expert opinion: Clinical trials performed so far demonstrated the importance to establish more reliable animal models and better correlates of protection. Defining appropriate endpoints for clinical trials of serotype-independent vaccine candidates has been a challenge. Inhibition of colonization has been evaluated, but concern on the extent of bacterial elimination is still a matter of debate. Challenges on establishing representative sites for clinical trials, sample sizes and appropriate age groups are discussed. On a whole, although many challenges will have to be overcome, establishing protein-based antigens as serotype-independent vaccines is still the best alternative against the huge burden of pneumococcal diseases in the world.

Next-Generation Whole-Cell Pneumococcal Vaccine

Streptococcus pneumoniae remains a major public health hazard. Although Pneumococcal Conjugate Vaccines (PCVs) are available and have significantly reduced the rate of invasive pneumococcal diseases, there is still a need for new vaccines with unlimited serotype coverage, long-lasting protection, and lower cost to be developed. One of the most promising candidates is the Whole-Cell Pneumococcal Vaccine (WCV). The new generation of whole-cell vaccines is based on an unencapsulated serotype that allows the expression of many bacterial antigens at a lower cost than a recombinant vaccine. These vaccines have been extensively studied, are currently in human trial phase 1/2, and seem to be the best treatment choice for pneumococcal diseases, especially for developing countries.

Panproteome-wide analysis of antibody responses to whole cell pneumococcal vaccination

Pneumococcal whole cell vaccines (WCVs) could cost-effectively protect against a greater strain diversity than current capsule-based vaccines. Immunoglobulin G (IgG) responses to a WCV were characterised by applying longitudinally-sampled sera, available from 35 adult placebo-controlled phase I trial participants, to a panproteome microarray. Despite individuals maintaining distinctive antibody ‘fingerprints’, responses were consistent across vaccinated cohorts. Seventy-two functionally distinct proteins were associated with WCV-induced increases in IgG binding. These shared characteristics with naturally immunogenic proteins, being enriched for transporters and cell wall metabolism enzymes, likely unusually exposed on the unencapsulated WCV’s surface. Vaccine-induced responses were specific to variants of the diverse PclA, PspC and ZmpB proteins, whereas PspA- and ZmpA-induced antibodies recognised a broader set of alleles. Temporal variation in IgG levels suggested a mixture of anamnestic and novel responses. These reproducible increases in IgG binding to a limited, but functionally diverse, set of conserved proteins indicate WCV could provide species-wide immunity.

Clinical trial registration: The trial was registered with ClinicalTrials.gov with Identifier NCT01537185; the results are available from https://clinicaltrials.gov/ct2/show/results/NCT01537185.

Streptococcus pneumoniae is a bug that causes pneumonia and meningitis, killing around a million people each year. Vaccines now exist to protect young children against these diseases, but they are expensive and do not work against all the strains of the bacteria. This is because these shots train the body’s immune system to recognize and attack the bacterium’s capsule, a layer of sugars that surrounds the microbe and is often different between strains.

One possible solution could be a cheap, whole cell vaccine. These injections expose the body to genetically modified S. pneumoniae that do not carry the capsule. Such treatment has now been tested in a small number of people during a clinical trial.

Here, Campo et al. use a technique known as panproteome array to scan samples collected during this trial, and identify which elements the body learns to recognize when it is exposed to the genetically manipulated strain of S. pneumoniae. The results show that when volunteers receive this vaccine, their body targets proteins that the capsule normally shields from the immune system. Many of these proteins are very similar across all strains of S. pneumoniae, which means that the whole cell vaccine could potentially better protect against a broad spectrum of bacteria. However, further studies are needed to assess whether this is the case, especially in infants.

Use of an individual-based model of pneumococcal carriage for planning a randomized trial of a whole-cell vaccine

For encapsulated bacteria such as Streptococcus pneumoniae, asymptomatic carriage is more common and longer in duration than disease, and hence is often a more convenient endpoint for clinical trials of vaccines against these bacteria. However, using a carriage endpoint entails specific challenges. Carriage is almost always measured as prevalence, whereas the vaccine may act by reducing incidence or duration. Thus, to determine sample size requirements, its impact on prevalence must first be estimated. The relationship between incidence and prevalence (or duration and prevalence) is convex, saturating at 100% prevalence. For this reason, the proportional effect of a vaccine on prevalence is typically less than its proportional effect on incidence or duration. This relationship is further complicated in the presence of multiple pathogen strains. In addition, host immunity to carriage accumulates rapidly with frequent exposures in early years of life, creating potentially complex interactions with the vaccine’s effect. We conducted a simulation study to predict the impact of an inactivated whole cell pneumococcal vaccine—believed to reduce carriage duration—on carriage prevalence in different age groups and trial settings. We used an individual-based model of pneumococcal carriage that incorporates relevant immunological processes, both vaccine-induced and naturally acquired. Our simulations showed that for a wide range of vaccine efficacies, sampling time and age at vaccination are important determinants of sample size. There is a window of favorable sampling times during which the required sample size is relatively low, and this window is prolonged with a younger age at vaccination, and in a trial setting with lower transmission intensity. These results illustrate the ability of simulation studies to inform the planning of vaccine trials with carriage endpoints, and the methods we present here can be applied to trials evaluating other pneumococcal vaccine candidates or comparing alternative dosing schedules for the existing conjugate vaccines.

Streptococcus pneumoniae, a bacterium carried in the nasopharynx of many healthy people, is also a leading cause of bacterial pneumonia, sepsis, and ear infections in children aged five years and younger. Vaccines targeting select strains of S. pneumoniae have been effective, and the development of new vaccines, particularly those that target all strains, can further lower disease burden. For clinical trials of these vaccines, the number of study participants needed depends on the expected effect of the vaccine on a conveniently measured outcome: asymptomatic carriage. The most economical way to test a vaccine for its effect on carriage is by measuring prevalence at a specific time, and comparing vaccinated to unvaccinated participants. The relationship between incidence (or duration) and prevalence is complex, and changes with time as children develop natural immunity. We explored this relationship using a mathematical model. Given a vaccine efficacy, our computer simulations predict that fewer study participants are needed if they are vaccinated at a younger age, taken from a population with intermediate levels of transmission, and sampled for carriage at a certain time window: 9 to 18 months after vaccination. Our study illustrates how simulation studies can help plan more efficient vaccine trials.

Construction and evaluation of a whole-cell pneumococcal vaccine candidate

AIMS

Pneumococcal infections are a major public health problem, especially in developing countries, and the current pneumococcal vaccines do not cover all pathogenic strains. New, more economical serotype-independent vaccines based on species-common protein antigens are being pursued. The pneumococcal whole-cell vaccine which is based on noncapsular antigens common to all strains induces serotype-independent immunity. In the present study, we developed a new candidate for a whole-cell pneumococcal vaccine in which two important virulence factors, the capsule and pneumolysin, were deleted.

METHODS AND RESULTS

Protection was elicited by immunization against colonization in mice with a killed mutant strain and the antibody response in the mice serum was evaluated. This candidate vaccine was effective in preventing nasopharyngeal colonization. The mice immunized with this candidate vaccine had significantly higher serum antibody titres than mice that received the adjuvant alone.

CONCLUSIONS

Based on obtained results in this study, the engineered whole-cell pneumococci can be considered as a vaccine candidate in future studies.

SIGNIFICANCE AND IMPACT OF THE STUDY

This candidate vaccine can overcome the limitations of available polysaccharide vaccines.

Efficacy of whole-cell pneumococcal vaccine in mice: A systematic review and meta-analysis

BACKGROUND

Despite the fact that pneumococcal conjugate vaccines (PCVs) have significantly reduced the rate of invasive pneumococcal diseases through the use of vaccine serotypes, infection with Streptococcus pneumoniae remains a major public health hazard. Serotype-independent vaccines that are economically viable species of common protein antigens such as whole-cell vaccines (WCVs) are needed. Considering the ongoing debate about the effectiveness of WCVs, a systematic literature review and meta-analysis was carried out to determine the efficacy of WCVs against colonization in mice.

MATERIAL AND METHODS

A systematic review was undertaken of published studies on the protection (colonized/uncolonized) of whole cell pneumococcal vaccine in mice. The search terms used were "whole cell vaccine" and "Streptococcus pneumoniae" in PubMed, Google Scholar, Embase, Web of Science and Scopus engines. Data was extracted from original publications and a meta-analysis was performed on studies divided into sub-groups by the number of inoculations, type of sample, type of adjuvant, time of sampling, design of study and quality of study.

RESULTS

Ten eligible articles published from 2000 to 2016 were included in this review. The meta-analysis was performed on eight out of 10 studies and demonstrated that the estimated pooled risk ratios (RRs) for comparison of colonization between the vaccinated and unvaccinated mice for outcomes 1 and 2 were 0.18 and 0.24, respectively. Lower RRs were observed in sub-groups that were inoculated with vaccines three times, those using cholera toxin (CT) adjuvants and those obtained as tracheal specimens from the mice.

CONCLUSIONS

The best protocol for use of a WCV is its application with CT adjuvant administered intranasally in three inoculations at doses of 10⁸ CFU. Further studies performed under similar conditions to obtain accurate results on the effectiveness of this vaccine are recommended.

Immunogenicity and mechanisms of action of PnuBioVax, a multi-antigen serotype-independent prophylactic vaccine against infection with Streptococcus pneumoniae

Streptococcus pneumoniae has multiple protein antigens on the surface in addition to the serotype specific polysaccharide capsule antigen. Whilst the capsule antigen is the target of the polysaccharide vaccines, bacterial proteins can also act as targets for the immune system. PnuBioVax (PBV) is being developed as a multi-antigen, serotype-independent prophylactic vaccine against S. pneumoniae disease. In this study we have sought to elucidate the immune response to PBV in immunised rabbits. Sera from PBV immunised rabbits contained high levels of IgG antibodies to the PBV vaccine, and pneumococcal antigens PspA, Ply, PsaA and PiuA which are components of PBV, when compared with control sera. The PBV sera supported killing of the vaccine strain TIGR4 in an opsonophagocytic killing assay and heterologous strains 6B, 19F and 15B. In addition, incubation in PBV sera led to agglutination of several strains of pneumococci, inhibition of Ply-mediated lysis of erythrocytes and reduced bacterial invasion of lung epithelial cells in vitro. These data suggest that PBV vaccination generates sera that has multiple mechanisms of action that may provide effective protection against pneumococcal infection and give broader strain coverage than the current polysaccharide based vaccines.

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.

The contrasting roles of Th17 immunity in human health and disease

The human immune system is a tightly regulated network that protects the host from disease. An important aspect of this is the balance between pro-inflammatory Th17 cells and anti-inflammatory T regulatory (Treg) cells in maintaining immune homeostasis. Foxp3+ Treg are critical for sustaining immune tolerance through IL-10 and transforming growth factor-β while related orphan receptor-γt+ Th17 cells promote immunopathology and auto-inflammatory diseases through the actions of IL-17A, IL-21 and IL-22. Therefore, imbalance between Treg and Th17 cells can result in serious pathology in many organs and tissues. Recently, certain IL-17-producing cells have been found to be protective against infectious disease, particularly in relation to extracellular bacteria such Streptococcus pneumoniae; a number of other novel IL-17-secreting cell populations have also been reported to protect against a variety of other pathogens. In this mini-review, the dual roles of Treg and Th17 cells are discussed in the context of autoimmunity and infections, highlighting recent advances in the field. Development of novel strategies specifically designed to target these critical immune response pathways will become increasingly important in maintenance of human health.

IL-17A and complement contribute to killing of pneumococci following immunization with a pneumococcal whole cell vaccine

The pneumococcal whole cell vaccine (PWCV) has been investigated as an alternative to polysaccharide-based vaccines currently in use. It is a non-encapsulated killed vaccine preparation that induces non-capsular antibodies protecting mice against invasive pneumococcal disease (IPD) and reducing nasopharyngeal (NP) carriage via IL-17A activation of mouse phagocytes. Here, we show that PWCV induces antibody and IL-17A production to protect mice against challenge in a fatal aspiration-sepsis model after only one dose. We observed protection even with a boiled preparation, attesting to the stability and robustness of the vaccine. PWCV antibodies were shown to bind to different encapsulated strains, but complement deposition on the pneumococcal surface was observed only on serotype 3 strains; using flow cytometer methodology, variations in PWCV quality, as in the boiled vaccine, were detected. Moreover, anti-PWCV induces phagocytosis of different pneumococcal serotypes by murine peritoneal cells in the presence of complement or IL-17A. These findings suggest that complement and IL-17A may participate in the process of phagocytosis induced by PWCV antibodies. IL-17A can stimulate phagocytic cells to kill pneumococcus and this is enhanced in the presence of PWCV antibodies bound to the bacterial cell surface. Our results provide further support for the PWCV as a broad-range vaccine against all existing serotypes, potentially providing protection for humans against NP colonization and IPD. Additionally, we suggest complement deposition assay as a tool to detect subtle differences between PWCV lots.

Recombinant expression of Streptococcus pneumoniae capsular polysaccharides in Escherichia coli

Currently, Streptococcus pneumoniae is responsible for over 14 million cases of pneumonia worldwide annually, and over 1 million deaths, the majority of them children. The major determinant for pathogenesis is a polysaccharide capsule that is variable and is used to distinguish strains based on their serotype. The capsule forms the basis of the pneumococcal polysaccharide vaccine (PPV23) that contains purified capsular polysaccharide from 23 serotypes, and the pneumococcal conjugate vaccine (PCV13), containing 13 common serotypes conjugated to CRM197 (mutant diphtheria toxin). Purified capsule from S. pneumoniae is required for pneumococcal conjugate vaccine production, and costs can be prohibitively high, limiting accessibility of the vaccine in low-income countries. In this study, we demonstrate the recombinant expression of the capsule-encoding locus from four different serotypes of S. pneumoniae within Escherichia coli. Furthermore, we attempt to identify the minimum set of genes necessary to reliably and efficiently express these capsules heterologously. These E. coli strains could be used to produce a supply of S. pneumoniae serotype-specific capsules without the need to culture pathogenic bacteria. Additionally, these strains could be applied to synthetic glycobiological applications: recombinant vaccine production using E. coli outer membrane vesicles or coupling to proteins using protein glycan coupling technology.

Streptococcus pneumoniae Endopeptidase O (PepO) Elicits a Strong Innate Immune Response in Mice via TLR2 and TLR4 Signaling Pathways

Interaction between virulence factors of Streptococcus pneumoniae and innate immune receptors elicits host responses through specific signaling pathways during infection. Insights into the signaling events may provide a better knowledge of the starting events for host-pathogen interaction. Here we demonstrated a significant induction of innate immune response elicited by recombinant S. pneumoniae endopeptidase O (rPepO), a newer pneumococcal virulence protein, both in vivo and in vitro. Intratracheal instillation of rPepO protein resulted in significant increase of cytokines production and neutrophils infiltration in mouse lungs. TLR2 or TLR4 deficient mice subjected to rPepO treatment showed decreased cytokines production, reduced neutrophils infiltration and intensified tissue injury as compared with WT mice. Upon stimulation, cytokines TNF-α, IL-6, CXCL1, and CXCL10 were produced by peritoneal exudate macrophages (PEMs) in a TLR2 and TLR4 dependent manner. rPepO-induced cytokines production was markedly decreased in TLR2 or TLR4 deficient PEMs. Further study revealed that cytokines induction relied on the rapid phosphorylation of p38, Akt and p65, not the activation of ERK or JNK. While in TLR2 or TLR4 deficient PEMs the activation of p65 was undetectable. Taken together, these results indicate for the first time that the newer pneumococcal virulence protein PepO activates host innate immune response partially through TLR2 and TLR4 signaling pathways.

Application of radiation technology in vaccines development

One of the earliest methods used in the manufacture of stable and safe vaccines is the use of chemical and physical treatments to produce inactivated forms of pathogens. Although these types of vaccines have been successful in eliciting specific humoral immune responses to pathogen-associated immunogens, there is a large demand for the development of fast, safe, and effective vaccine manufacturing strategies. Radiation sterilization has been used to develop a variety of vaccine types, because it can eradicate chemical contaminants and penetrate pathogens to destroy nucleic acids without damaging the pathogen surface antigens. Nevertheless, irradiated vaccines have not widely been used at an industrial level because of difficulties obtaining the necessary equipment. Recent successful clinical trials of irradiated vaccines against pathogens and tumors have led to a reevaluation of radiation technology as an alternative method to produce vaccines. In the present article, we review the challenges associated with creating irradiated vaccines and discuss potential strategies for developing vaccines using radiation technology.

GHIP in Streptococcus pneumoniae is involved in antibacterial resistance and elicits a strong innate immune response through TLR2 and JNK/p38MAPK

Interaction between pneumococcal virulence factors and innate immune receptors triggers host responses via specific signaling pathways after infection. By generating a deficient mutant, we show here that, compared with the wild-type parent strain, glycosyl hydrolase 25 relating to invasion protein (GHIP) mutant strain was impaired in rapid dissemination into vessels and caused less severe inflammation in mice lungs. Further study demonstrated that the lack of this protein in Streptococcus pneumoniae caused an increased susceptibility to whole blood or neutrophils, while this impairment could be recovered by supplementing recombinant GHIP (rGHIP). Additionally, secreted GHIP could be detected in culture medium, and purified protein was able to induce the release of tumor necrosis factor α and interleukin 6 from peritoneal macrophages. Further investigations revealed that the induction of interleukin 6 by this virulence factor depended on the phosphorylation of c-Jun N-terminal kinase and p38 mitogen activated protein kinase and Toll-like receptor 2. Taken together, GHIP, a novel pneumococcal virulence factor, appeared to play a critical role in bacterial survival and the induction of host innate immune response during pneumococcal infection.