PppA, a surface-exposed protein of Streptococcus pneumoniae, elicits cross-reactive antibodies that reduce colonization in a murine intranasal immunization and challenge model

Molecular Characterization Based on Whole-Genome Sequencing of Streptococcus pneumoniae in Children Living in Southwest China During 2017-2019

Background

Streptococcus pneumoniae is an important pathogen causing high morbidity and high mortality in children and undergoes frequent recombination for capsule switching to neutralize the 13-valent pneumococcal conjugate vaccine (PCV13). This study aimed to investigate the prevalence, and molecular characteristics including serotypes and antibiotic susceptibility of S. pneumoniae isolated from children living in Southwest China from 2017 to 2019 to facilitate the selection of effective vaccine formulations and appropriate antibiotic treatment regimens.

Methods

This study was conducted at West China Second University Hospital (Chengdu, Sichuan Province, China), Zunyi Medical University Third Affiliated Hospital/First People's Hospital of Zunyi (Zunyi, Guizhou Province, China) and Chengdu Jinjiang District Maternal and Child Healthcare Hospital (Chengdu, Sichuan Province, China). Demographic and clinical characteristics of children infected with S. pneumoniae were collected and analysed. Next-generation sequencing and sequence analysis were used to determine the serotypes, sequence types, antibiotic resistance and potential protein vaccine target genes of the pneumococcal isolates. The coverage rate provided by PCV13 was estimated by calculating the percentage of the specific serotypes that were specifically the PCV13-included serotypes. Antimicrobial susceptibility was determined by the microdilution broth method.

Results

The most prevalent pneumococcal serotypes were 19F (25.8%), 19A (14.1%), 6B (12.5%), 6A (9.4%) and 14 (7.8%). The predominant STs were ST271 (23.3%), ST320 (15.5%) and ST90 (8.6%), dominated by the clonal complex Taiwan^19F-14 (39.1%). The coverage rate of PCV13 was 77.3% in all the isolates, with relatively higher values in invasive isolates (86.4%). Over the decade, the rates of resistance to penicillin, amoxicillin and cefotaxime were 5.6%, 5.3% and 5.1%, respectively, with significantly higher values in invasive isolates (22.4%, 14.9% and 11.9%). Almost all the isolates were resistant to erythromycin (99.1%) and clindamycin (95.9%). All isolates carried virulence-related genes, including ply, psaA, piaA, piuA, phtE, nanA, pepO, danJ, pvaA, clpP, pcsB, stkP, potD, and strH. The carriage of virulence and resistance genes varied among serotypes and clades, with serotype 19F/ST271 showing higher resistance to antibiotics and being more likely to carry pilus genes and other virulence genes.

Conclusion

These data provide valuable information for the understanding of pneumococcal pathogenesis, antimicrobial resistance and the development of protein-based vaccines against pneumococcal infection.

In vivo screen of genetically conserved Streptococcus pneumoniae proteins for protective immunogenicity

We evaluated 52 different E. coli expressed pneumococcal proteins as immunogens in a BALB/c mouse model of S. pneumoniae lung infection. Proteins were selected based on genetic conservation across disease-causing serotypes and bioinformatic prediction of antibody binding to the target antigen. Seven proteins induced protective responses, in terms of reduced lung burdens of the serotype 3 pneumococci. Three of the protective proteins were histidine triad protein family members (PhtB, PhtD and PhtE). Four other proteins, all bearing LPXTG linkage domains, also had activity in this model (PrtA, NanA, PavB and Eng). PrtA, NanA and Eng were also protective in a CBA/N mouse model of lethal pneumococcal infection. Despite data inferring widespread genomic conservation, flow-cytometer based antisera binding studies confirmed variable levels of antigen expression across a panel of pneumococcal serotypes. Finally, BALB/c mice were immunized and intranasally challenged with a viulent serotype 8 strain, to help understand the breadth of protection. Those mouse studies reaffirmed the effectiveness of the histidine triad protein grouping and a single LPXTG protein, PrtA.

Protein transduction domain of transactivating transcriptional activator fused to outer membrane protein K of Vibrio parahaemolyticus to vaccinate marbled eels (Anguilla marmorata) confers protection against mortality caused by V. parahaemolyticus

Although immersion and oral vaccination are the most practical methods for fish farmers, their applications are very limited due to low immune stimulation effect. We used the protein transduction domain (PTD) of transactivating transcriptional factor (TAT) derived from HIV TAT protein to increase the delivery efficiency of aquatic protein vaccines. Vibrio parahaemolyticus outer membrane protein K (ompK), a reported vaccine candidate for the prevention of V. parahaemolyticus infection, was fused with TAT-PTD expressed in Escherichia coli. We found that PTD-ompK fusion protein effectively penetrated into marbled eel bodies. Analysis of ompK antibody titres demonstrated that immersion vaccination with PTD-ompK was superior to ompK alone and induced robust immune stimulation in marbled eels. Both active and passive protection analyses against immersive challenge with V. parahaemolyticus strains demonstrated that marbled eels immunized with PTD-ompK survived significantly longer than those immunized with ompK alone. Our results indicated that TAT-PTD could be served as is an efficient delivery system for aquatic immersion vaccinations against various infectious diseases commonly seen in aquatic farm industry.

Effect of nonheme iron-containing ferritin Dpr in the stress response and virulence of pneumococci

Streptococcus pneumoniae (pneumococcus) produces hydrogen peroxide as a by-product of metabolism and provides a competitive advantage against cocolonizing bacteria. As pneumococci do not produce catalase or an inducible regulator of hydrogen peroxide, the mechanism of resistance to hydrogen peroxide is unclear. A gene responsible for resistance to hydrogen peroxide and iron in other streptococci is that encoding nonheme iron-containing ferritin, dpr, but previous attempts to study this gene in pneumococcus by generating a dpr mutant were unsuccessful. In the current study, we found that dpr is in an operon with the downstream genes dhfr and clpX. We generated a dpr deletion mutant which displayed normal early-log-phase and mid-log-phase growth in bacteriologic medium but survived less well at stationary phase; the addition of catalase partially rescued the growth defect. We showed that the dpr mutant is significantly more sensitive to pH, heat, iron concentration, and oxidative stress due to hydrogen peroxide. Using a mouse model of colonization, we also showed that the dpr mutant displays a reduced ability to colonize and is more rapidly cleared from the nasopharynx. Our results thus suggest that Dpr is important for pneumococcal resistance to stress and for nasopharyngeal colonization.

Immune response in nasopharynx, lung, and blood elicited by experimental nasal pneumococcal vaccines containing live or heat-killed lactobacilli as mucosal adjuvants

This work analyzes the humoral and cellular immune responses induced by live (LcV) and heat-killed (LcM) Lactobacillus casei associated with the pneumococcal antigen (P-Ag) at the nasopharynx level, considering nasal-associated lymphoid tissue (NALT) as the primary inductive site of the mucosal immune system, and lung and blood as effector sites. Levels of P-Ag IgA and IgG antibodies, main types of B and T cells, and cytokines in mucosal and systemic compartments were evaluated. The results showed that both LcM+P-Ag and LcV+P-Ag vaccines effectively induced IgA and IgG anti-P-Ag Abs in the upper and lower respiratory tract and plasma. These results correlated with increased IgA+ cells in NALT and lung that was induced by the experimental vaccines. Moreover, numbers of IgG+ cells increased in the blood. Profiles of inflammatory and regulatory cytokines were evaluated and their possible implications for the defense against pneumococci was assessed. Considering the overall results, the potential mechanisms of immune stimulation induced by LcM and LcV used as adjuvants are discussed. LcV and LcM showed similar effects on the immune system. Strain viability is not crucial for the stimulation of the antigen-specific immune response, and LcM is a convenient and effective mucosal adjuvant.

Development of Streptococcus pneumoniae Vaccines Using Live Vectors

Streptococcus pneumoniae still causes severe morbidity and mortality worldwide, especially in young children and the elderly. Much effort has been dedicated to developing protein-based universal vaccines to conquer the current shortcomings of capsular vaccines and capsular conjugate vaccines, such as serotype replacement, limited coverage and high costs. A recombinant live vector vaccine delivering protective antigens is a promising way to achieve this goal. In this review, we discuss the researches using live recombinant vaccines, mainly live attenuated Salmonella and lactic acid bacteria, to deliver pneumococcal antigens. We also discuss both the limitations and the future of these vaccines.

Identification of potential new protein vaccine candidates through pan-surfomic analysis of pneumococcal clinical isolates from adults

Purified polysaccharide and conjugate vaccines are widely used for preventing infections in adults and in children against the Gram-positive bacterium Streptococcus pneumoniae, a pathogen responsible for high morbidity and mortality rates, especially in developing countries. However, these polysaccharide-based vaccines have some important limitations, such as being serotype-dependent, being subjected to losing efficacy because of serotype replacement and high manufacturing complexity and cost. It is expected that protein-based vaccines will overcome these issues by conferring a broad coverage independent of serotype and lowering production costs. In this study, we have applied the “shaving” proteomic approach, consisting of the LC/MS/MS analysis of peptides generated by protease treatment of live cells, to a collection of 16 pneumococcal clinical isolates from adults, representing the most prevalent strains circulating in Spain during the last years. The set of unique proteins identified in all the isolates, called “pan-surfome”, consisted of 254 proteins, which included most of the protective protein antigens reported so far. In search of new candidates with vaccine potential, we identified 32 that were present in at least 50% of the clinical isolates analyzed. We selected four of them (Spr0012, Spr0328, Spr0561 and SP670_2141), whose protection capacity has not yet been tested, for assaying immunogenicity in human sera. All of them induced the production of IgM antibodies in infected patients, thus indicating that they could enter the pipeline for vaccine studies. The pan-surfomic approach shows its utility in the discovery of new proteins that can elicit protection against infectious microorganisms.

Human pathogenic streptococcal proteomics and vaccine development

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

Identification of protective pneumococcal T(H)17 antigens from the soluble fraction of a killed whole cell vaccine

Mucosal or parenteral immunization with a killed unencapsulated pneumococcal whole cell antigen (WCA) with an adjuvant protects mice from colonization by a T(H)17 CD4+ cell-mediated mechanism. Using preparative SDS gels, we separated the soluble proteins that compose the WCA in order to identify fractions that were immunogenic and protective. We screened these fractions for their ability to stimulate IL-17A secretion from splenocytes obtained from mice immunized with WCA and adjuvant. We identified 12 proteins within the stimulatory fractions by mass spectrometry; these proteins were then cloned, recombinantly expressed and purified using an Escherichia coli expression system. The ability of these proteins to induce IL-17A secretion was then evaluated by stimulation of mouse splenocytes. Of the four most stimulatory proteins, three were protective in a mouse pneumococcal serotype 6B colonization model. This work thus describes a method for identifying immunogenic proteins from the soluble fraction of pneumococcus and shows that several of the proteins identified protect mice from colonization when used as mucosal vaccines. We propose that, by providing protection against pneumococcal colonization, one or more of these proteins may serve as components of a multivalent pneumococcal vaccine.

Development of vaccine delivery vehicles based on lactic acid bacteria

Live recombinant bacteria represent attractive antigen delivery systems able to induce both mucosal and systemic immune responses against heterologous antigens. The first live recombinant bacterial vectors developed were derived from attenuated pathogenic microorganisms. In addition to the difficulties often encountered in the construction of stable attenuated mutants of pathogenic organisms, attenuated pathogens may retain a residual virulence level that renders them unsuitable for the vaccination of partially immunocompetent individuals such as infants, the elderly or immunocompromised patients. As an alternative to this strategy, non-pathogenic food-grade lactic acid bacteria (LAB) maybe used as live antigen carriers. This article reviews LAB vaccines constructed using antigens other than tetanus toxin fragment C, against bacterial, viral, and parasitic infective agents, for which protection studies have been performed. The antigens utilized for the development of LAB vaccines are briefly described, along with the efficiency of these systems in protection studies. Moreover, the key factors affecting the performance of these systems are highlighted.

A bivalent vaccine to protect against Streptococcus pneumoniae and Salmonella typhi

Pneumococcal and Salmonella typhi infections are two major diseases for children in developing countries. For typhoid fever, licensed Vi polysaccharide vaccines are ineffective in children <2-year old. While investigational Vi conjugate vaccines have been shown effective in clinical trials, they are currently only available to restricted areas. Pneumococcal capsular polysaccharide conjugate vaccines are highly effective in children, but suffer from some limitations including cost and limited serotype coverage. We have previously shown that a fusion conjugate vaccine, consisting of pneumococcal fusion protein PsaA and pneumolysoid (PdT) conjugated to a polysaccharide, results in enhanced antibody and CD4+ Th17 cell responses as well as protection against pneumococcal colonization and disease in mice. Here we applied this approach to develop a bivalent vaccine against pneumococcus and S. typhi. Two species-conserved pneumococcal antigens (SP1572 or SP2070) were fused to the nonhemolytic pneumolysoid PdT. SP1572-PdT was then conjugated to Vi polysaccharide and SP2070-PdT was conjugated to the pneumococcal cell wall polysaccharide (CWPS; also conserved). Mice immunized with this bivalent conjugate were protected against pneumococcal colonization and sepsis challenges, and made anti-Vi antibody concentrations higher by 40-fold compared to mice that received equimolar mixtures of the antigens. An enhanced killing of Vi-bearing Salmonellae in vitro was demonstrated from plasma of mice that received the fusion conjugate but not the mixture of antigens. Our results support further evaluation of this bivalent immunogen for the prevention of pneumococcal colonization and disease, and of typhoid fever.

Host immunity in the protective response to nasal immunization with a pneumococcal antigen associated to live and heat-killed Lactobacillus casei

Background

At present, available pneumococcal vaccines have failed to eradicate infections caused by S. pneumoniae. Search for effective vaccine continues and some serotype independent pneumococcal proteins are considered as candidates for the design of new vaccines, especially a mucosal vaccine, since pneumococci enter the body through mucosal surfaces. Selection of the appropriate adjuvant is important for mucosal vaccines, and lactic acid bacteria (LAB) with immunostimulant properties are promissory candidates. In this work, we assessed the adjuvant effect of a probiotic strain, Lactobacillus casei (L. casei), when nasally administered with a pneumococcal antigen (pneumococcal protective protein A: PppA) for the prevention of pneumococcal infection. Adjuvanticity of both live (LcV) and heat-killed (LcM) was evaluated and humoral and cellular antigen-specific immune response was assessed in mucosal and systemic compartments. The potential mechanisms induced by nasal immunization were discussed.

Results

Nasal immunization of young mice with PppA+LcV and PppA+LcM induced anti-PppA IgA and IgG antibodies in mucosal and systemic compartments and levels of these specific antibodies remained high even at day 45 after the 3rd Immunization (3rd I). These results were correlated with IL-4 induction by the mixture of antigen plus LcV and LcM. Also, PppA+Lc (V and M) induced stimulation of Th1 and Th17 cells involved in the defence against pneumococci. The protection against pneumococcal respiratory challenge at day 30 after the 3rd I showed that PppA+LcV and PppA+LcM immunizations significantly reduced pathogen counts in nasal lavages while prventing their passage into lung and blood. Survival of mice immunized with the co-application of PppA plus LcV and LcM was significantly higher than in mice immunized with PppA alone and control mice when intraperitoneal challenge was performed. No significant differences between the treatments involving LcV and LcM were found.

Conclusions

Live and heat-killed L. casei enhanced the antigen-specific immune response when administered nasally with a pneumococcal antigen. Considering the potential risk associated with live bacteria, the design of a nasal vaccine based on pneumococcal antigens and heat-killed L. casei emerges as a safe and effective strategy for the prevention of pneumococcal infections and opens new possibilities of application of dead LAB as adjuvants in vaccine formulations against other pathogens.

Lactic acid bacteria in the prevention of pneumococcal respiratory infection: future opportunities and challenges

Lactic acid bacteria (LAB) are technologically and commercially important and have various beneficial effects on human health. Several studies have demonstrated that certain LAB strains can exert their beneficial effect on the host through their immunomudulatory activity. Although most research concerning LAB-mediated enhanced immune protection is focused on gastrointestinal tract pathogens, recent studies have centered on whether these immunobiotics might sufficiently stimulate the common mucosal immune system to provide protection to other mucosal sites as well. In this sense, LAB have been used for the development of probiotic foods with the ability to stimulate respiratory immunity, which would increase resistance to infections, even in immunocompromised hosts. On the other hand, the advances in the molecular biology of LAB have enabled the development of recombinant strains expressing antigens from respiratory pathogens that have proved effective to induce protective immunity. In this review we examine the current scientific literature concerning the use of LAB strains to prevent respiratory infections. In particular, we have focused on the works that deal with the capacity of probiotic and recombinant LAB to improve the immune response against Streptococcus pneumoniae. Research from the last decade demonstrates that LAB represent a promising resource for the development of prevention strategies against respiratory infections that could be effective tools for medical application.

Next generation pneumococcal vaccines

Currently licensed pneumococcal vaccines are based on the generation of antibodies to the pneumococcal polysaccharide, of which there are more than 90 different types. While these vaccines are highly effective against the serotypes included, their high cost and limited serotype coverage limit their usefulness worldwide, particularly in low resource areas. Thus alternative or adjunctive options are being actively pursued. This review will present these various approaches, including variations of the polysaccharide-protein conjugate strategy, protein-based strategies, and whole cell pneumococcal vaccines. The immunological basis for these different approaches is discussed as well.

Cloning and optimization of induction conditions for mature PsaA (pneumococcal surface adhesin A) expression in Escherichia coli and recombinant protein stability during long-term storage

The gene corresponding to mature PsaA from Streptococcus pneumoniae serotype 14 was cloned into a plasmid with kanamycin resistance and without a purification tag in Escherichia coli to express high levels of the recombinant protein for large-scale production as a potential vaccine candidate or as a carrier for polysaccharide conjugation at Bio-Manguinhos/Fiocruz. The evaluation of induction conditions (IPTG concentration, temperature and time) in E. coli was accomplished by experimental design techniques to enhance the expression level of mature recombinant PsaA (rPsaA). The optimization of induction process conditions led us to perform the recombinant protein induction at 25°C for 16 h, with 0.1mM IPTG in Terrific Broth medium. At these conditions, the level of mature rPsaA expression obtained in E. coli BL21 (DE3) Star by pET28a induction with IPTG was in the range of 0.8 g/L of culture medium, with a 10-fold lower concentration of inducer than usually employed, which contributes to a less expensive process. Mature rPsaA expressed in E. coli BL21 (DE3) Star accounted for approximately 30-35% of the total protein. rPsaA purification by ion exchange allowed the production of high-purity recombinant protein without fusion tags. The results presented in this work confirm that the purified recombinant protein maintains its stability and integrity for long periods of time in various storage conditions (temperatures of 4 or -70°C using different cryoprotectors) and for at least 3 years at 4 or -70°C in PBS. The conformation of the stored protein was confirmed using circular dichroism. Mature rPsaA antigenicity was proven by anti-rPsaA mouse serum recognition through western blot analysis, and no protein degradation was detected after long periods of storage.

Structure and dynamics of the pan-genome of Streptococcus pneumoniae and closely related species

Background

Streptococcus pneumoniae is one of the most important causes of microbial diseases in humans. The genomes of 44 diverse strains of S. pneumoniae were analyzed and compared with strains of non-pathogenic streptococci of the Mitis group.

Results

Despite evidence of extensive recombination, the S. pneumoniae phylogenetic tree revealed six major lineages. With the exception of serotype 1, the tree correlated poorly with capsular serotype, geographical site of isolation and disease outcome. The distribution of dispensable genes - genes present in more than one strain but not in all strains - was consistent with phylogeny, although horizontal gene transfer events attenuated this correlation in the case of ancient lineages. Homologous recombination, involving short stretches of DNA, was the dominant evolutionary process of the core genome of S. pneumoniae. Genetic exchange occurred both within and across the borders of the species, and S. mitis was the main reservoir of genetic diversity of S. pneumoniae. The pan-genome size of S. pneumoniae increased logarithmically with the number of strains and linearly with the number of polymorphic sites of the sampled genomes, suggesting that acquired genes accumulate proportionately to the age of clones. Most genes associated with pathogenicity were shared by all S. pneumoniae strains, but were also present in S. mitis, S. oralis and S. infantis, indicating that these genes are not sufficient to determine virulence.

Conclusions

Genetic exchange with related species sharing the same ecological niche is the main mechanism of evolution of S. pneumoniae. The open pan-genome guarantees the species a quick and economical response to diverse environments.

Administration of a probiotic associated with nasal vaccination with inactivated Lactococcus lactis-PppA induces effective protection against pneumoccocal infection in young mice

Streptococcus pneumoniae is a serious public health problem, especially in developing countries, where available vaccines are not part of the vaccination calendar. We evaluated different respiratory mucosa immunization protocols that included the nasal administration of Lactococcus lactis-pneumococcal protective protein A (PppA) live, inactivated, and in association with a probiotic (Lc) to young mice. The animals that received Lc by the oral and nasal route presented the highest levels of immunoglobulin (Ig)A and IgG anti-PppA antibodies in bronchoalveolar lavages (BAL) and IgG in serum, which no doubt contributed to the protection against infection. However, only the groups that received the live and inactivated vaccine associated with the oral administration of the probiotic were able to prevent lung colonization by S. pneumoniae serotypes 3 and 14 in a respiratory infection model. This would be related to a preferential stimulation of the T helper type 1 (Th1) cells at local and systemic levels and with a moderate Th2 and Th17 response, shown by the cytokine profile induced in BAL and by the results of the IgG1/IgG2a ratio at local and systemic levels. Nasal immunization with the inactivated recombinant strain associated with oral Lc administration was able to stimulate the specific cellular and humoral immune response and afford protection against the challenge with the two S. pneumoniae serotypes. The results obtained show the probiotic-inactivated vaccine association as a valuable alternative for application to human health, especially in at-risk populations, and are the first report of a safe and effective immunization strategy using an inactivated recombinant strain.

Development of 5-valent conjugate pneumococcal protein A - Capsular polysaccharide pneumococcal vaccine against invasive pneumococcal disease

In this study, we synthesized a 5-valent pneumococcal conjugate vaccine, which was prepared with the pneumococcal capsular polysaccharides (PCPs) (from Streptococcus pneumoniae 1, 5, 6B, 19F, 23F) and pneumococcal surface protein A (PspA) mediated by 1,4-butanediol diglycidyl ether. The PspA cloned from serotype 19 strain showed good cross-immune response to 1, 5, 6B, and 23F serotypes of Streptococcus pneumonia (S. pneumoniae). Analysis of the maturation process of conjugate polyclonal antibody showed that conjugation with the protein carrier converted the polysaccharide from a weak T cell-independent (TI) antigen to a T cell-dependent (TD) antigen, although antibodies affinity to polysaccharide was not as strong as it to PspA in conjugate. We used an invasive disease mouse model to evaluate the protective efficacy of this conjugate vaccine. Active and passive protection against intraperitoneal challenge with virulent type 6B strain showed that the median survival times for mice immunized with conjugate were significantly longer than that of mice treated with capsular polysaccharides or PspA alone. Our study's results showed that immunization of the 5-valent PspA-capsular polysaccharides conjugate vaccine could afford strong protection to mice against the invasion of 1, 5, 6B, 19F, 23F serotypes S. pneumoniae.

Mucosal immunization with polyamine transport protein D (PotD) protects mice against nasopharyngeal colonization with Streptococcus pneumoniae

Streptococcus pneumoniae is an encapsulated pathogen that can cause invasive disease following colonization of the nasopharynx. Targeting colonization of mucosal surfaces may, therefore, be the best approach for vaccination to prevent pneumococcal invasive disease. Previous studies in our laboratory have shown that immunization with recombinant polyamine transport protein D (PotD) protects mice against systemic pneumococcal infections. In this study we investigated the efficacy of mucosal immunization with rPotD to protect against pneumococcal carriage and invasion in a murine model. Mice were intranasally immunized with either rPotD and cholera toxin B subunit (CTB) or CTB alone. Significantly less pneumococci were recovered from the nasopharynx of immunized mice compared to the control animals following intranasal challenge with either EF3030 (serotype 19F) (P < 0.05) or an invasive serotype 4 isolate (TIGR4) (P < 0.05). PotD immunized mice also had lesser bacteria in their sinus tissues (P < 0.05), brains (P < 0.05), lungs and olfactory bulbs following intranasal challenge with TIGR4. ELISA analysis demonstrated the presence of IgG antibodies to PotD in the serum and IgA antibodies in the saliva. These results indicate that mucosal immunization with PotD generates both mucosal and systemic immune responses and prevents establishment of nasopharyngeal carriage by multiple pneumococcal serotypes. Thus, PotD is a potentially important antigen for development of a pneumococcal protein vaccine.

Oral immunization with recombinant Lactococcus lactis confers protection against respiratory pneumococcal infection

In the present work, we evaluated if oral immunization with the pneumococcal protective protein A (PppA), expressed in the cell wall of Lactococcus lactis (L. lactis PppA+), was able to confer protective immunity against Streptococcus pneumoniae. Mice were immunized orally with L. lactis PppA+ for 5 consecutive days. Vaccination was performed one (nonboosted group) or 2 times with a 2 week interval between each immunization (boosted group). Oral priming with L. lactis PppA+ induced the production of anti-PppA IgM, IgG, and IgA antibodies in serum and in bronchoalveolar (BAL) and intestinal (IF) lavage fluids. Boosting with L. lactis PppA+ increased the levels of mucosal and systemic immunoglobulins. Moreover, the avidity and the opsonophagocytic activity of anti-PppA antibodies were significantly improved in the boosted group. The presence of both IgG1 and IgG2a anti-PppA antibodies in serum and BAL and the production of both interferon gamma and interleukin-4 by spleen cells from immunized mice indicated that L. lactis PppA+ stimulated a mixture of Th1 and Th2 responses. The ability of L. lactis PppA+ to confer cross-protective immunity was evaluated using challenge assays with serotypes 3, 6B, 14, and 23F. Lung bacterial cell counts and hemocultures showed that immunization with L. lactis PppA+ improved resistance against all the serotypes assessed, including serotype 3, which was highly virulent in our experimental animal model. To our knowledge, this is the first demonstration of protection against respiratory pneumococcal infection induced by oral administration of a recombinant lactococcal vaccine.

Streptococcus pneumoniaeProtein Vaccine Candidates: Properties, Activities and Animal Studies

Streptococcus pneumoniae is a causative agent for community acquired pneumonia, bacteremia, acute otitis media, and meningitis. Recent emergence of multi-drug resistant clinical isolates prompts the need of effective vaccine for the prevention of disease. The licensed polysaccharide-based pneumococcal vaccines only elicit protective antibodies against the infection of serotypes that are included in the vaccine. To broaden the protection, the use of pneumococcal proteins will be a feasible and preferable alternative. This communication provides a review on the biochemical properties of these protein candidates, their immunization results in animal studies, and perspectives on the development of protein-based pneumococcal vaccine.

Nasal immunization with Lactococcus lactis expressing the pneumococcal protective protein A induces protective immunity in mice

Nisin-controlled gene expression was used to develop a recombinant strain of Lactococcus lactis that is able to express the pneumococcal protective protein A (PppA) on its surface. Immunodetection assays confirmed that after the induction with nisin, the PppA antigen was predictably and efficiently displayed on the cell surface of the recombinant strain, which was termed L. lactis PppA. The production of mucosal and systemically specific antibodies in adult and young mice was evaluated after mice were nasally immunized with L. lactis PppA. Immunoglobulin M (IgM), IgG, and IgA anti-PppA antibodies were detected in the serum and bronchoalveolar lavage fluid of adult and young mice, which showed that PppA expressed in L. lactis was able to induce a strong mucosal and systemic immune response. Challenge survival experiments demonstrated that immunization with L. lactis PppA was able to increase resistance to systemic and respiratory infection with different pneumococcal serotypes, and passive immunization assays of naïve young mice demonstrated a direct correlation between anti-PppA antibodies and protection. The results presented in this study demonstrate three major characteristics of the effectiveness of nasal immunization with PppA expressed as a protein anchored to the cell wall of L. lactis: it elicited cross-protective immunity against different pneumococcal serotypes, it afforded protection against both systemic and respiratory challenges, and it induced protective immunity in mice of different ages.

Mouse models of otitis media

PURPOSE OF REVIEW

Otitis media is one of the most prevalent inflammatory diseases in the pediatric population. The personal and societal costs for otitis media are significant. Problems arising from antibiotic use have led to considerable animal research efforts to better understand the mechanisms of acute otitis media and to develop new strategies for its prevention and treatment.

RECENT FINDINGS

Various animal models induce acute otitis media from a variety of interventions, including direct injection of whole bacteria or their products into the middle ear. The mouse model has begun to emerge as a model for otitis media. The mouse affords many advantages for in-vivo research, including ease of genetic manipulation, availability of numerous inbred and transgenic strains, and an extensively studied immune system. Experimental reagents for cellular and molecular studies are widely available for the mouse. The mouse is an excellent model for investigating the genetics and molecular bases for otitis media due to the extensive understanding of the mouse genome.

SUMMARY

With the increased availability of knockout and transgenic mice, and the large amount of data to indicate that human disease is accurately modeled in the mouse, the mouse model is increasingly becoming a model of choice.

Mouse models for the study of mucosal vaccination against otitis media

Otitis media (OM) is one of the most common infectious diseases in humans. The pathogenesis of OM involves nasopharyngeal (NP) colonization and retrograde ascension of the pathogen up the Eustachian tube into the middle ear (ME). Due to increasing rates of antibiotic resistance, there is an urgent need for vaccines to prevent infections caused by the most common causes of bacterial OM, including nontypeable Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis. Current vaccine strategies aim to diminish bacterial NP carriage, thereby reducing the likelihood of developing acute OM. To be effective, vaccination should induce local mucosal immunity both in the ME and in the NP. Studies in animal models have demonstrated that the intranasal route of vaccination is particularly effective at inducing immune responses in the nasal passage and ME for protection against OM. The mouse is increasingly used in these models, because of the availability of murine reagents and the existence of technology to manipulate murine models of disease immunologically and genetically. Previous studies confirmed the suitability of the mouse as a model for inflammatory processes in acute OM. Here, we discuss various murine models of OM and review the applicability of these models to assess the efficacy of mucosal vaccination and the mechanisms responsible for protection. In addition, we discuss various mucosal vaccine antigens, mucosal adjuvants and mucosal delivery systems.

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.

Development of lactococcal GEM-based pneumococcal vaccines

We report the development of a novel protein-based nasal vaccine against Streptococcus pneumoniae, in which three pneumococcal proteins were displayed on the surface of a non-recombinant, killed Lactococcus lactis-derived delivery system, called Gram-positive Enhancer Matrix (GEM). The GEM particles induced the production of the proinflammatory cytokine tumour necrosis factor-alpha (TNF-alpha) by macrophages as well as the maturation of dendritic cells. The pneumococcal proteins IgA1 protease (IgA1p), putative proteinase maturation protein A (PpmA) and streptococcal lipoprotein A (SlrA) were anchored in trans to the surface of the GEM particles after recombinant production of the antigens in L. lactis as hybrids with a lactococcal cell wall binding domain, named Protein Anchor domain (PA). Intranasal immunisation with the SlrA-IgA1p or trivalent vaccine combinations without additional adjuvants showed significant protection against fatal pneumococcal pneumonia in mice. The GEM-based trivalent vaccine is a potential pneumococcal vaccine candidate that is expected to be easy to administer, safe and affordable to produce.

Experimental infection of rhesus macaques with Streptococcus pneumoniae: a possible model for vaccine assessment

BACKGROUND

We explored the possibility of using normal adult rhesus macaques for the preclinical assessment of safety, immunogenicity, and efficacy of newly developed vaccines against Streptococcus pneumoniae infection of the lung.

METHODS

Our primary objective was to determine whether an intra-bronchial inoculum of at least 10(6)S. pneumoniae colony-forming units, or one as high as 10(8)-10(9) organisms, could detectably survive in rhesus macaques for a period longer than 1-2 weeks. If so, we hypothesized, it would be possible to observe signs of pneumonia commonly observed in humans, and discriminate between vaccinated/protected animals and controls. Infection was detectable in bronchoalveolar lavage fluids 3-5 weeks post-inoculation.

RESULTS

The clinical course of disease mimicked aspects of that of human pneumococcal pneumonia. Signs of inflammation typical of the disease in humans, such as elevated concentrations of neutrophils and of pro-inflammatory cytokines in bronchoalveolar lavage fluids were also observed.

CONCLUSIONS

These findings underscore the utility of this model to assess the safety, immunogenicity, and efficacy of newly developed S. pneumoniae vaccines.

Advances in understanding the pathogenesis of pneumococcal otitis media

In this review, a state of the art on otitis media research is provided with emphasis on the role of Streptococcus pneumoniae in the pathogenesis of this disease. Articles have been selected by MEDLINE search supplemented with a manual crosscheck of bibliographies. Pathogenic mechanisms in middle ear and eustachian tube are described. Furthermore, pneumococcal characteristics and pneumococcus-host interactions are highlighted as well as the possible role of biofilms in persistence or recurrence of otitis media. Because of the availability of new techniques, an increasing number of pneumococcal features contributing in the pathogenesis of otitis media are identified and in-depth knowledge of pneumococcus-host interactions has been gained. The present advances in research on otitis media open up new perspectives for therapeutic or preventive strategies.

Intranasal immunization of mice with recombinant lipidated P2086 protein reduces nasal colonization of group B Neisseria meningitidis

Neisseria meningitidis is a major cause of bacterial meningitis in the human population, especially among young children. There is a need to develop a non-capsular vaccine to prevent meningococcal B infections due to the inadequate immune response elicited against the capsular polysaccharide of these strains. Previously, we developed a Swiss Webster adult mouse intranasal challenge model for group B N. meningitidis and evaluated several potential vaccine candidates including a meningococcal outer membrane protein, P2086, through parenteral immunization. Since N. meningitidis is a respiratory pathogen, a mucosal immune response may play an important role in the defense against meningococcal infections. Thus, intranasal immunization may be more effective than traditional parenteral immunization. In this study, mice were immunized intranasally with purified recombinant lipidated P2086 protein (rLP2086) adjuvanted with either CT-E29H, a genetically modified cholera toxin that is significantly reduced in enzymatic activity and toxicity or RC529-AF, a synthetic immunostimulant molecule in aqueous formulation. rLP2086-specific serum and mucosal IgG and IgA antibodies were induced. IgG antibodies reacted with whole cells of multiple strains of group B N.meningitidis. The antibodies have functional activity against N. meningitidis as demonstrated by bactericidal assays. Moreover, immunized mice exhibited reduced nasal colonization of group B meningococcal strains in the intranasal challenge model. These results demonstrate that an intranasal immunization with rLP2086 protein formulated with a detoxified cholera toxin or RC529-AF could prevent the initial colonization of group B meningococcus and become an effective immunization strategy against group B N. meningitidis.