Efficacy of a conjugate vaccine containing polymannuronic acid and flagellin against experimental Pseudomonas aeruginosa lung infection in mice

A Semisynthetic Oligomannuronic Acid-Based Glycoconjugate Vaccine against Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the leading causes of nosocomial infections and has become increasingly resistant to multiple antibiotics. However, development of novel classes of antibacterial agents against multidrug-resistant P. aeruginosa is extremely difficult. Herein we develop a semisynthetic oligomannuronic acid-based glycoconjugate vaccine that confers broad protection against infections of both mucoid and nonmucoid strains of P. aeruginosa. The well-defined glycoconjugate vaccine formulated with Freund's adjuvant (FA) employing a highly conserved antigen elicited a strong and specific immune response and protected mice against both mucoid and nonmucoid strains of P. aeruginosa. The resulting antibodies recognized different strains of P. aeruginosa and mediated the opsonic killing of the bacteria at varied levels depending on the amount of alginate expressed on the surface of the strains. Vaccination with the glycoconjugate vaccine plus FA significantly promoted the pulmonary and blood clearance of the mucoid PAC1 strain of P. aeruginosa and considerably improved the survival rates of mice against the nonmucoid PAO1 strain of P. aeruginosa. Thus, the semisynthetic glycoconjugate is a promising vaccine that may provide broad protection against both types of P. aeruginosa.

Microwave-assisted synthesis of highly sulfated mannuronate glycans as potential inhibitors against SARS-CoV-2

Algae-based marine carbohydrate drugs are typically decorated with negative ion groups such as carboxylate and sulfate groups. However, the precise synthesis of highly sulfated alginates is challenging, thus impeding their structure-activity relationship studies. Herein we achieve a microwave-assisted synthesis of a range of highly sulfated mannuronate glycans with up to 17 sulfation sites by overcoming the incomplete sulfation due to the electrostatic repulsion of crowded polyanionic groups. Although the partially sulfated tetrasaccharide had the highest affinity for the receptor binding domain (RBD) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant, the fully sulfated octasaccharide showed the most potent interference with the binding of the RBD to angiotensin-converting enzyme 2 (ACE2) and Vero E6 cells, indicating that the sulfated oligosaccharides might inhibit the RBD binding to ACE2 in a length-dependent manner.

The O-glycan is essential for the induction of protective antibodies against lethal infection by flagella A-bearing Pseudomonas aeruginosa

To address the problem of increased antimicrobial resistance, we developed a glycoconjugate vaccine comprised of O-polysaccharides (OPS) of the four most prevalent serotypes of Klebsiella pneumoniae (KP) linked to recombinant flagellin types A and B (rFlaA and rFlaB) of Pseudomonas aeruginosa (PA). Flagellin is the major subunit of the flagellar filament. Flagella A and B, essential virulence factors for PA, are glycosylated with different glycans. We previously reported that while both rFlaA and rFlaB were highly immunogenic, only the rFlaB antisera reduced PA motility and protected mice from lethal PA infection in a mouse model of thermal injury. Since recombinant flagellin is not glycosylated, we examined the possibility that the glycan on native FlaA (nFlaA) might be critical to functional immune responses. We compared the ability of nFlaA to that of native, deglycosylated FlaA (dnFlaA) to induce functionally active antisera. O glycan was removed from nFlaA with trifluoromethanesulfonic acid. Despite the similar high-titered anti-FlaA antibody levels elicited by nFlaA, rFlaA, and dnFlaA, only the nFlaA antisera inhibited PA motility and protected mice following lethal intraperitoneal bacterial challenge. Both the protective efficacy and carrier protein function of nFlaA were retained when conjugated to KP O1 OPS. We conclude that unlike the case with FlaB O glycan, the FlaA glycan is an important epitope for the induction of functionally active anti-FlaA antibodies.

A chimeric vaccine targeting Pseudomonas aeruginosa virulence factors protects mice against lethal infection

Pseudomonas aeruginosa is an important and hazardous nosocomial pathogen in respiratory tract infections and rapidly achieves antibiotic resistance, so it is necessary to develop an effective vaccine to combat the infection. The Type III secretion system (T3SS) protein P. aeruginosa V-antigen (PcrV), outer membrane protein F (OprF), and two kinds of flagellins (FlaA and FlaB) all play important roles in the pathogenesis of P. aeruginosa lung infection and its spread into deeper tissues. In a mouse acute pneumonia model, the protective effects of a chimer vaccine including PcrV, FlaA, FlaB, and OprF (PABF) protein were investigated. PABF immunization prompted robust opsonophagocytic titer of IgG antibodies and decreased bacterial burden, and improved survival afterward intranasal challenge with ten times 50% lethal doses (LD50) of P. aeruginosa strains, indicating its broad-spectrum immunity. Moreover, these findings showed a promise chimeric vaccine candidate to treat and control P. aeruginosa infections.

Synthesis and Immunogenicity of a Methyl Rhamnan Pentasaccharide Conjugate from Pseudomonas aeruginosa A-Band Polysaccharide

Pseudomonas aeruginosa was added to the World Health Organization's priority pathogen list for research and development of new antibiotics in 2017. Alongside the development of new antibiotics to fight antimicrobial-resistant P. aeruginosa, vaccines would be an appealing addition to the toolbox health professionals have against this bacteria, which causes life-threatening respiratory infections. Recently, the structure of a novel immunogenic terminal carbohydrate moiety on the cell surface of P. aeruginosa was elucidated, consisting of a 3-O-methyl (1→4)-α-d-rhamnan pentasaccharide. As isolating this oligosaccharide from P. aeruginosa in sufficient amounts for producing a conjugate vaccine is challenging, herein we describe the synthesis of 3-O-methyl d-rhamnose oligosaccharide. We also report the conjugation of the synthetic pentasaccharide to human serum albumin and its resulting immunogenicity.

Vaccines for multidrug resistant Gram negative bacteria: lessons from the past for guiding future success

Antimicrobial resistance is a major threat to global public health. Vaccination is an effective approach for preventing bacterial infections, however it has not been successfully applied to infections caused by some of the most problematic multidrug resistant pathogens. In this review, the potential for vaccines to contribute to reducing the burden of disease of infections caused by multidrug resistant Gram negative bacteria is presented. Technical, logistical and societal hurdles that have limited successful vaccine development for these infections in the past are identified, and recent advances that can contribute to overcoming these challenges are assessed. A synthesis of vaccine technologies that have been employed in the development of vaccines for key multidrug resistant Gram negative bacteria is included, and emerging technologies that may contribute to future successes are discussed. Finally, a comprehensive review of vaccine development efforts over the last 40 years for three of the most worrisome multidrug resistant Gram negative pathogens, Acinetobacter baumannii, Klebsiella pneumoniae and Pseudomonas aeruginosa is presented, with a focus on recent and ongoing studies. Finally, future directions for the vaccine development field are highlighted.

Immunization against Pseudomonas aeruginosa using Alg-PLGA nano-vaccine

OBJECTIVES

Pseudomonas aeruginosa is the bacterium that causes of pulmonary infection among chronically hospitalized patients. Alginate is a common surface antigen of P. aeruginosa with a constant structure that which makes it an appropriate target for vaccines. In this study, P. aeruginosa alginate was conjugated with to PLGA nanoparticles, and its immunogenicity was characterized as a vaccine.

MATERIALS AND METHODS

Alginate was isolated from a mucoid strain of P. aeruginosa and conjugated with to PLGA with˝ N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride ˝= ˝EDAC˝ and N-Hydroxysuccinimide (NHS). Chemical characterization of prepared nano-vaccine was performed using FTIR Spectroscopy, Zetasizer, and Atomic Force Microscopy (AFM). The immunogenicity of this nano-vaccine was evaluated through intramuscular injection into BALB/c mice. Four groups of mice were subjected to the injection of alginate-PLGA, and two weeks after the last administration step, opsonophagocytosis assay, IgG detection, challenge, and cytokine determination via ELISA were carried out.

RESULTS

Alginate-PLGA conjugation was corroborated by FTIR, Zetasizer, and AFM. The ELISA consequence showed that alginate was prospering in the instigation of the humoral immunity.The immunogenicity enhanced against the alginate-PLGA. Remarkably diminished bacterial titer in the spleen of the immunized mice posterior to challenge with PAO1 strain in comparison with the alginate alone and control groups.

CONCLUSION

The bacterial burden in the spleen significantly decreased after the challenge (P<0.05). The opsonic activity was significantly increased in the alginate- PLGA group (P<0.05).

Hematological Picture of Rabbits Immunized with Pseudomonas aeruginosa

The current study was established to find out the role of immunization of Pseudomonas aeruginosa-whole sonicated antigen in adult white fur domestic rabbits. To achieve this goal, fifteen rabbits were allocated into 3 groups, the first group was immunized with P. aeruginosa–whole sonicated antigen and challenged with viable pathogenic P. aeruginosa; the second group (control negative) was treated with phosphate buffer saline and the third group was injected with viable pathogenic P. aeruginosa (control positive). The results demonstrated increasing levels of the measured parameters blood picture (total WBCs, lymphocytes, and granulocytes, RBCs and hemoglobin concentrations) in the first group compared with control negative group (T test was used). In contrast, a sharp fall was noted in total thrombocytes (platelets) count in the first group compared with control negative group. It can be concluded that immunization with P. aeruginosa– whole sonicated antigen may consider as a potent reproducible effective immunogen model for experimental immunological studies in rabbits.

Understanding Pseudomonas aeruginosa-Host Interactions: The Ongoing Quest for an Efficacious Vaccine

Pseudomonas aeruginosa is a leading cause of chronic respiratory infections in people with cystic fibrosis (CF), bronchiectasis or chronic obstructive pulmonary disease (COPD), and acute infections in immunocompromised individuals. The adaptability of this opportunistic pathogen has hampered the development of antimicrobial therapies, and consequently, it remains a major threat to public health. Due to its antimicrobial resistance, vaccines represent an alternative strategy to tackle the pathogen, yet despite over 50 years of research on anti-Pseudomonas vaccines, no vaccine has been licensed. Nevertheless, there have been many advances in this field, including a better understanding of the host immune response and the biology of P. aeruginosa. Multiple antigens and adjuvants have been investigated with varying results. Although the most effective protective response remains to be established, it is clear that a polarised Th2 response is sub-optimal, and a mixed Th1/Th2 or Th1/Th17 response appears beneficial. This comprehensive review collates the current understanding of the complexities of P. aeruginosa-host interactions and its implication in vaccine design, with a view to understanding the current state of Pseudomonal vaccine development and the direction of future efforts. It highlights the importance of the incorporation of appropriate adjuvants to the protective antigen to yield optimal protection.

Novel therapeutic strategies for treating Pseudomonas aeruginosa infection

INTRODUCTION

Persistent infections caused by the superbug Pseudomonas aeruginosa and its resistance to multiple antimicrobial agents are huge threats to patients with cystic fibrosis as well as those with compromised immune systems. Multidrug-resistant P. aeruginosa has posed a major challenge to conventional antibiotics and therapeutic approaches, which show limited efficacy and cause serious side effects. The public demand for new antibiotics is enormous; yet, drug development pipelines have started to run dry with limited targets available for inventing new antibacterial drugs. Consequently, it is important to uncover potential therapeutic targets.

AREAS COVERED

The authors review the current state of drug development strategies that are promising in terms of the development of novel and potent drugs to treat P. aeruginosa infection.

EXPERT OPINION

The prevention of P. aeruginosa infection is increasingly challenging. Furthermore, targeting key virulence regulators has great potential for developing novel anti-P. aeruginosa drugs. Additional promising strategies include bacteriophage therapy, immunotherapies, and antimicrobial peptides. Additionally, the authors believe that in the coming years, the overall network of molecular regulatory mechanism of P. aeruginosa virulence will be fully elucidated, which will provide more novel and promising drug targets for treating P. aeruginosa infections.

Constructing conjugate vaccine against Salmonella Typhimurium using lipid-A free lipopolysaccharide

Background

Salmonella enterica serotype Typhimurium is a nontyphoidal and common foodborne pathogen that causes serious threat to humans. There is no licensed vaccine to prevent the nontyphoid bacterial infection caused by S. Typhimurium.

Methods

To develop conjugate vaccines, the bacterial lipid-A free lipopolysaccharide (LFPS) is prepared as the immunogen and used to synthesize the LFPS–linker–protein conjugates 6a–9b. The designed bifunctional linkers 1–5 comprising either an o-phenylenediamine or amine moiety are specifically attached to the exposed 3-deoxy-D-manno-octulosonic acid (Kdo), an α-ketoacid saccharide of LFPS, via condensation reaction or decarboxylative amidation. In addition to bovine serum albumin and ovalbumin, the S. Typhimurium flagellin (FliC) is also used as a self-adjuvanting protein carrier.

Results

The synthesized conjugate vaccines are characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and fast performance liquid chromatography (FPLC), and their contents of polysaccharides and protein are determined by phenol–sulfuric acid assay and bicinchoninic acid assay, respectively. Enzyme-linked immunosorbent assay (ELISA) shows that immunization of mouse with the LFPS–linker–protein vaccines at a dosage of 2.5 μg is sufficient to elicit serum immunoglobulin G (IgG) specific to S. Typhimurium lipopolysaccharide (LPS). The straight-chain amide linkers in conjugates 7a–9b do not interfere with the desired immune response. Vaccines 7a and 7b derived from either unfractionated LFPS or the high-mass portion show equal efficacy in induction of IgG antibodies. The challenge experiments are performed by oral gavage of S. Typhimurium pathogen, and vaccine 7c having FliC as the self-adjuvanting protein carrier exhibits a high vaccine efficacy of 74% with 80% mice survival rate at day 28 post the pathogen challenge.

Conclusions

This study demonstrates that lipid-A free lipopolysaccharide prepared from Gram-negative bacteria is an appropriate immunogen, in which the exposed Kdo is connected to bifunctional linkers to form conjugate vaccines. The decarboxylative amidation of Kdo is a novel and useful method to construct a relatively robust and low immunogenic straight-chain amide linkage. The vaccine efficacy is enhanced by using bacterial flagellin as the self-adjuvanting carrier protein.

Graphical abstract

Highly convergent synthesis of a β-mannuronic acid alginate hexadecasaccharide

Solution-phase synthesis of poly-β-mannuronic acids still remains unexplored. We report the first synthesis of a β-mannuronic acid alginate hexadecasaccharide representing the longest synthetic polymannuronic acid so far. The highly convergent synthetic approach provides a new avenue to access poly-β-mannuronic acids that can enable the biological evaluation of poly-β-mannuronic acids as potential therapeutics and vaccines.

Pseudomonas aeruginosa keratitis: passive immunotherapy with antibodies raised against divalent flagellin

Objective(s):

Pseudomonas aeruginosa infections such as keratitis are considered among the major health problems worldwide due to the complexity of pathogenesis and antibiotic resistance crisis, thus, finding new effective approaches for prevention and treatment of the infections seem to be still vital. In this report, we aimed to investigate the therapeutic effects of topical administration of the antibodies against type a and b-flagellin (FLA and FLB) in Pseudomonas keratitis model of infection in mice.

Materials and Methods:

Scratched corneas of mice were treated with approximately 10⁷ CFUs/eye of PAK and/or PAO1 strains of P. aeruginosa. Specific IgG to FLA, FLB or divalent flagellin were topically applied to the infected corneas for 20 min, 24, and 36 hr post-infection. The bacterial burden and myeloperoxidase activity (as a marker for polymorphonuclears (PMNs) infiltration) were determined in the corneas. The biological activity of the anti-FLA and FLB IgG was evaluated in vitro by opsonophagocytosis test.

Results:

Compared to other treated corneas, divalent anti-flagellin IgG treatment showed a significant decrease in the bacterial CFUs and myeloperoxidase activity in the infected corneas (P<0.05). Results of opsonophagocytosis revealed that the specific antibodies raised against FLA and FLB had more potent opsonic killing activity on their homologous strains as compared with control group (P<0.05).

Conclusion:

It appears that in P. aeruginosa keratitis, topical administration of the combined antibodies likely via decreasing the bacterial load, and PMNs infiltration as well as increasing opsonophagocytosis could lead to dramatic improvement of the infected corneas.

Mechanistic research holds promise for bacterial vaccines and phage therapies for Pseudomonas aeruginosa

Vaccines for Pseudomonas aeruginosa have been of longstanding interest to immunologists, bacteriologists, and clinicians, due to the widespread prevalence of hospital-acquired infection. As P. aeruginosa becomes increasingly antibiotic resistant, there is a dire need for novel treatments and preventive vaccines. Despite intense efforts, there currently remains no vaccine on the market to combat this dangerous pathogen. This article summarizes current and past vaccines under development that target various constituents of P. aeruginosa. Targeting lipopolysaccharides and O-antigens have shown some promise in preventing infection. Recombinant flagella and pili that target TLR5 have been utilized to combat P. aeruginosa by blocking its motility and adhesion. The type 3 secretion system components, such as needle-like structure PcrV or exotoxin PopB, are also potential vaccine targets. Outer membrane proteins including OprF and OprI are newer representatives of vaccine candidates. Live attenuated vaccines are a focal point in this review, and are also considered for novel vaccines. In addition, phage therapy is revived as an effective option for treating refractory infections after failure with antibiotic treatment. Many of the aforementioned vaccines act on a single target, thus lacking a broad range of protection. Recent studies have shown that mixtures of vaccines and combination approaches may significantly augment immunogenicity, thereby increasing their preventive and therapeutic potential.

Potential targets for next generation antimicrobial glycoconjugate vaccines

Cell surface carbohydrates have been proven optimal targets for vaccine development. Conjugation of polysaccharides to a carrier protein triggers a T-cell-dependent immune response to the glycan moiety. Licensed glycoconjugate vaccines are produced by chemical conjugation of capsular polysaccharides to prevent meningitis caused by meningococcus, pneumococcus and Haemophilus influenzae type b. However, other classes of carbohydrates (O-antigens, exopolysaccharides, wall/teichoic acids) represent attractive targets for developing vaccines. Recent analysis from WHO/CHO underpins alarming concern toward antibiotic-resistant bacteria, such as the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) and additional pathogens such as Clostridium difficile and Group A Streptococcus. Fungal infections are also becoming increasingly invasive for immunocompromised patients or hospitalized individuals. Other emergencies could derive from bacteria which spread during environmental calamities (Vibrio cholerae) or with potential as bioterrorism weapons (Burkholderia pseudomallei and mallei, Francisella tularensis). Vaccination could aid reducing the use of broad-spectrum antibiotics and provide protection by herd immunity also to individuals who are not vaccinated.

This review analyzes structural and functional differences of the polysaccharides exposed on the surface of emerging pathogenic bacteria, combined with medical need and technological feasibility of corresponding glycoconjugate vaccines.

Development of a broad spectrum glycoconjugate vaccine to prevent wound and disseminated infections with Klebsiella pneumoniae and Pseudomonas aeruginosa

Klebsiella pneumoniae (KP) and Pseudomonas aeruginosa (PA) are important human pathogens that are associated with a range of infection types, including wound and disseminated infections. Treatment has been complicated by rising rates of antimicrobial resistance. Immunoprophylactic strategies are not constrained by antimicrobial resistance mechanisms. Vaccines against these organisms would be important public health tools, yet they are not available. KP surface O polysaccharides (OPS) are protective antigens in animal models of infection. Similarly, PA flagellin (Fla), the major subunit of the flagellar filament, is required for virulence and is a target of protective antibodies in animal models. We report herein the development of a combined KP and PA glycoconjugate vaccine comprised of the four most common KP OPS types associated with human infections (O1, O2, O3, O5), chemically linked to the two Fla types of PA (FlaA, FlaB). Conjugation of KP OPS to PA Fla enhanced anti-polysaccharide immune responses and produced a formulation that generated antibody titers to the four KP OPS types and both PA Fla antigens in rabbits. Passive transfer of vaccine-induced rabbit antisera reduced the bacterial burden and protected mice against fatal intravenous KP infection. Mice passively transferred with conjugate-induced antisera were also protected against PA infection after thermal injury with a FlaB-expressing isolate, but not a FlaA isolate. Taken together, these promising preclinical results provide important proof-of-concept for a broad spectrum human vaccine to prevent KP and PA infections.

Evaluation of the immune responses following co-administration of PilQ and type b-flagellin from Pseudomonas aeruginosa in the burn mouse model

Considering the increased antibiotic resistance of Pseudomonas aeruginosa, the evaluation of immune response against the antigens of this bacterium seems necessary. In this study, the protective efficacy and immunological properties of P. aeruginosa recombinant PilQ (r-PilQ) and type b-flagellin (FLB) proteins was evaluated in the burn mouse model of infection. The inbred BALB/c mice were immunized with r-PilQ and FLB antigens. To investigate the type of induced immune response, sera were analyzed by ELISA for total IgG, IgG1, and IgG2a isotypes. After the final immunization, the IL-4, IFN-γ, and IL-17 cytokines level were examined in the spleen of non-challenged mice. Fifty days after lethal challenge, the survival rate and bacterial burden in the skin and other internal organs of experimental mice were assessed. The in vivo administration of r-PilQ, FLB and combined antigen resulted in a significant increase in the survival of mice (66%, 75%, and 83%, respectively) infected by the PAO1 strain of P. aeruginosa in the burn model of infection. Immunization of mice with r-PilQ and FLB mixture induced high titers of IL-4 and IL-17 cytokines compared to control groups (P < 0.05). The high titer of antisera raised against combined antigen was able to inhibit the systemic spread of the PAO1 strain from the site of infection to the internal organs. We concluded that the parallel role of IL-4 and IL-17 is necessary for elimination of the bacteria and promotion of survival in the immunized burn mice.

Rational design, preparation and characterization of recombinant Ag85B variants and their glycoconjugates with T-cell antigenic activity against Mycobacterium tuberculosis

Tuberculosis is the deadliest infectious disease in the world. The variable efficacy of the current treatments highlights the need for more effective agents against this disease. In the past few years, we focused on the investigation of antigenic glycoconjugates starting from recombinant Ag85B (rAg85B), a potent protein antigen from Mycobacterium tuberculosis. In this paper, structural modifications were rationally designed in order to obtain a rAg85B variant protein able to maintain its immunogenicity after glycosylation. Lysine residues involved in the main T-epitope sequences (namely, K30 and K282) have been substituted with arginine to prevent their glycosylation by a lysine-specific reactive linker. The effectiveness of the mutation strategy and the detailed structure of resulting neo-glycoconjugates have been studied by intact mass spectrometry, followed by peptide and glycopeptide mapping. The effect of K30R and K282R mutations on the T-cell activity of rAg85B has also been investigated with a preliminary immunological evaluation performed by enzyme-linked immunospotting on the different variant proteins and their glycosylation products. After glycosylation, the two variant proteins with an arginine in position 30 completely retain the original T-cell activity, thus representing adequate antigenic carriers for the development of efficient glycoconjugate vaccines against tuberculosis.

Site-Selective Functionalization of Flagellin by Steric Self-Protection: A Strategy To Facilitate Flagellin as a Self-Adjuvanting Carrier in Conjugate Vaccine

Flagellin (FliC) can act as a carrier protein in the preparation of conjugate vaccines to elicit a T-cell-dependent immune response and as an intrinsic adjuvant to activate the toll-like receptor 5 (TLR5) to enhance vaccine potency. To enable the use of FliC as a self-adjuvanting carrier, an effective method for site-selective modification (SSM) of pertinent amino-acid residues in the D2 and D3 domains of FliC is explored without excessive modification of the D0 and D1 domains, which are responsible for activating and binding with TLR5. In highly concentrated Na₂ SO₄ solution, FliC monomers form flagellar filaments, in which the D0 and D1 domains are situated inside the tubular structure. Thus, the lysine residues (K219, K224, K324, and K331) in the D2 and D3 domains of flagellin are selectively modified by a diazo-transfer reaction with imidazole-1-sulfonyl azide. The sites with azido modification are confirmed by MALDI-TOF-MS, ESI-TOF-MS, and LC-MS/MS analyses along with label-free quantitation. The azido-modified filament dissolves to give FliC monomers, which can conjugate with alkyne-hinged saccharides by the click reaction. Transmission electron microscopy imaging, dynamic light scattering measurements, and the secreted embryonic alkaline phosphatase reporter assay indicate that the modified FliC monomers retain the ability either to bind with TLR5 or to reassemble into filaments. Overall, this study establishes a feasible method for the SSM of FliC by steric self-protection of the D0 and D1 domains.

Immunization with Bivalent Flagellin Protects Mice against Fatal Pseudomonas aeruginosa Pneumonia

Pseudomonas aeruginosa lung infections present a major challenge to healthcare systems worldwide because they are commonly associated with high morbidity and mortality. Here, we demonstrate the protective efficacy of type a and b flagellins (bivalent flagellin) against acute fatal pneumonia in mice. Mice immunized intranasally with a bivalent flagellin vaccine were challenged by different flagellated strains of P. aeruginosa in an acute pneumonia model. Besides the protective effect of the vaccine, we further measured the host innate and cellular immunity responses. The immunized mice in our study were protected against both strains. Remarkably, active immunization with type a or b flagellin significantly improved survival of mice against heterologous strain compared to flagellin a or b antisera. We also showed that after an intranasal challenge by P. aeruginosa strain, neutrophils are recruited to the airways of vaccinated mice, and that the bivalent flagellin vaccine was proved to be protective by the generated CD4⁺IL-17⁺ Th17 cells. In conclusion, bivalent flagellin vaccine can confer protection against different strains of P. aeruginosa in an acute pneumonia mouse model by eliciting effective cellular and humoral immune responses, including increased IL-17 production and improved opsonophagocytic killing.

Vaccine strategies against cystic fibrosis pathogens

A great number of cystic fibrosis (CF) pathogens such as Pseudomonas aeruginosa, the Burkholderia cepacia and the Mycobacterium abscessus complex raised difficult therapeutic problems due to their intrinsic multi-resistance to numerous antibiotics. Vaccine strategies represent one of the key weapons against these multi-resistant bacteria in a number of clinical settings like CF. Different strategies are considered in order to develop such vaccines, linked either to priming the host response, or by exploiting genomic data derived from the bacterium. Interestingly, virulence factors synthesized by various pathogens might serve as targets for vaccine development and have been, for example, evaluated in the context of CF.

Polymannuronic acid ameliorated obesity and inflammation associated with a high-fat and high-sucrose diet by modulating the gut microbiome in a murine model

Polymannuronic acid (PM), one of numerous alginates isolated from brown seaweeds, is known to possess antioxidant activities. In this study, we examined its potential role in reducing body weight gain and attenuating inflammation induced by a high-fat and high-sucrose diet (HFD) as well as its effect on modulating the gut microbiome in mice. A 30-d PM treatment significantly reduced the diet-induced body weight gain and blood TAG levels (P2·0). PM also had a profound impact on the microbial composition in the gut microbiome and resulted in a distinct microbiome structure. For example, PM significantly increased the abundance of a probiotic bacterium, Lactobacillus reuteri (log10 LDA score>2·0). Together, our results suggest that PM may exert its immunoregulatory effects by enhancing proliferation of several species with probiotic activities while repressing the abundance of the microbial taxa that harbor potential pathogens. Our findings should facilitate mechanistic studies on PM as a potential bioactive compound to alleviate obesity and the metabolic syndrome.

Frontline Science: Nasal epithelial GM-CSF contributes to TLR5-mediated modulation of airway dendritic cells and subsequent IgA response

Flagellin, as a TLR5 agonist, is an established mucosal adjuvant for enhancing mucosal IgA responses by i.n. immunization. Nasal epithelial cells (NECs) are the first sentinel cells to be exposed to antigen and adjuvant in i.n. immunization, and it is suggested that they play an important role in the mucosal adjuvant activity of flagellin. However, the molecular mechanism leading to modulation and the response by flagellin-activated NECs remain unknown. We aimed to identify the soluble mediator(s) from flagellin-activated NECs that modulate the functions of airway dendritic cells (DCs) and enhance subsequent IgA response. In vitro studies showed that compared with the TLR4 agonist LPS, flagellin directly triggered slight up-regulation of CD80 on airway DCs but was insufficient to affect CD86 expression and DC-mediated IgA response. With the use of an in vitro system for culturing mouse primary NECs (mNECs), we demonstrated that flagellin-activated mNECs could functionally modulate airway DCs, which manifested as significant up-regulation of CD80/CD86 and enhancement of IgA production. The functional modulation of airway DCs was dependent on TLR5 activation of mNECs rather than direct TLR5 activation of airway DCs. With the use of cytokine array and antibody-blocking assays, we further identified that GM-CSF, a cytokine secreted from TLR5-activated mNECs, contributes to the activation of mNECs to airway DCs and subsequent IgA enhancement. In vivo blocking experiments confirmed that GM-CSF is an important factor in recombinant flagellin derived from Salmonella typhi (FliC)-induced airway DC activation and antigen-specific IgA enhancement. Our data directly demonstrate that nasal epithelial GM-CSF contributes to TLR5-mediated modulation of airway DCs and a subsequent IgA response.

Polysaccharide conjugate vaccine protein carriers as a "neglected valency" - Potential and limitations

The development of vaccines against polysaccharide-encapsulated pathogens (e.g. Haemophilus influenzae type b, pneumococci, meningococci) is challenging because polysaccharides do not elicit a strong and long-lasting immune response (i.e. T-cell independent). This can be overcome by conjugating the polysaccharide to a protein carrier (e.g. tetanus toxoid, cross-reacting material 197 [CRM]), which vastly improves the immune response and induces memory to the polysaccharide (T-cell dependent). Although it is well documented that protein carriers additionally induce an immune response against themselves, this potential "additional valency" has so far not been recognized. The only exception is for the protein D carrier (derived from non-typeable Haemophilus influenzae [NTHi]) used in a pneumococcal conjugate vaccine, which may have a beneficial impact on NTHi acute otitis media. In this review, we describe the immunogenicity of various protein carriers and discuss their potential dual function: as providers of T-cell helper epitopes and as protective antigens. If this "additional valency" could be proven to be protective, it may be possible to consider its potential effect on the number of required immunizations. We also describe the potential for positive or negative interference between conjugate vaccines using the same protein carriers, the resulting desire for novel carriers, and information on potential new carriers. The range of conjugate vaccines is ever expanding, with different carriers and methods of conjugation. We propose that new conjugate vaccine trials should assess immunogenicity to both the polysaccharide and carrier. Ultimately, this so-far "neglected valency" could be an exploitable characteristic of polysaccharide conjugate vaccines.

Efficacy comparison of adjuvants in PcrV vaccine against Pseudomonas aeruginosa pneumonia

Vaccination against the type III secretion system of P. aeruginosa is a potential prophylactic strategy for reducing the incidence and improving the poor prognosis of P. aeruginosa pneumonia. In this study, the efficacies of three different adjuvants, Freund's adjuvant (FA), aluminum hydroxide (alum) and CpG oligodeoxynucleotide (ODN), were examined from the viewpoint of inducing PcrV-specific immunity against virulent P. aeruginosa. Mice that had been immunized intraperitoneally with recombinant PcrV formulated with one of the above adjuvants were challenged intratracheally with a lethal dose of P. aeruginosa. The PcrV-FA immunized group attained a survival rate of 91%, whereas the survival rates of the PcrV-alum and PcrV-CpG groups were 73% and 64%, respectively. In terms of hypothermia recovery after bacterial instillation, PcrV-alum was the most protective, followed by PcrV-FA and PcrV-CpG. The lung edema index was lower in the PcrV-CpG vaccination group than in the other groups. PcrV-alum immunization was associated with the greatest decrease in myeloperoxidase in infected lungs, and also decreased the number of lung bacteria to a similar number as in the PcrV-FA group. There was less neutrophil recruitment in the lungs of mice vaccinated with PcrV-alum or PcrV-CpG than in those of mice vaccinated with PcrV-FA or PcrV alone. Overall, in terms of mouse survival the PcrV-CpG vaccine, which could be a relatively safe next-generation vaccine, showed a comparable effect to the PcrV-alum vaccine.

Porcine Dendritic Cells as an In Vitro Model to Assess the Immunological Behaviour of Streptococcus suis Subunit Vaccine Formulations and the Polarizing Effect of Adjuvants

An in vitro porcine bone marrow-derived dendritic cell (DC) culture was developed as a model for evaluating immune polarization induced by adjuvants when administered with immunogens that may become vaccine candidates if appropriately formulated. The swine pathogen Streptococcus suis was chosen as a prototype to evaluate proposed S. suis vaccine candidates in combination with the adjuvants Poly I:C, Quil A ®, Alhydrogel ®, TiterMax Gold ® and Stimune ®. The toll-like receptor ligand Poly I:C and the saponin Quil A ® polarized swine DC cytokines towards a type 1 phenotype, with preferential production of IL-12 and TNF-α. The water-in-oil adjuvants TiterMax Gold ® and Stimune ® favoured a type 2 profile as suggested by a marked IL-6 release. In contrast, Alhydrogel ® induced a type 1/type 2 mixed cytokine profile. The antigen type differently modified the magnitude of the adjuvant effect, but overall polarization was preserved. This is the first comparative report on swine DC immune activation by different adjuvants. Although further swine immunization studies would be required to better characterize the induced responses, the herein proposed in vitro model is a promising approach that helps assessing behaviour of the vaccine formulation rapidly at the pre-screening stage and will certainly reduce numbers of animals used while advancing vaccinology science.

Pangenome-wide and molecular evolution analyses of the Pseudomonas aeruginosa species

BACKGROUND

Drug treatments and vaccine designs against the opportunistic human pathogen Pseudomonas aeruginosa have multiple issues, all associated with the diverse genetic traits present in this pathogen, ranging from multi-drug resistant genes to the molecular machinery for the biosynthesis of biofilms. Several candidate vaccines against P. aeruginosa have been developed, which target the outer membrane proteins; however, major issues arise when attempting to establish complete protection against this pathogen due to its presumably genotypic variation at the strain level. To shed light on this concern, we proposed this study to assess the P. aeruginosa pangenome and its molecular evolution across multiple strains.

RESULTS

The P. aeruginosa pangenome was estimated to contain more than 16,000 non-redundant genes, and approximately 15 % of these constituted the core genome. Functional analyses of the accessory genome indicated a wide presence of genetic elements directly associated with pathogenicity. An in-depth molecular evolution analysis revealed the full landscape of selection forces acting on the P. aeruginosa pangenome, in which purifying selection drives evolution in the genome of this human pathogen. We also detected distinctive positive selection in a wide variety of outer membrane proteins, with the data supporting the concept of substantial genetic variation in proteins probably recognized as antigens. Approaching the evolutionary information of genes under extremely positive selection, we designed a new Multi-Locus Sequencing Typing assay for an informative, rapid, and cost-effective genotyping of P. aeruginosa clinical isolates.

CONCLUSIONS

We report the unprecedented pangenome characterization of P. aeruginosa on a large scale, which included almost 200 bacterial genomes from one single species and a molecular evolutionary analysis at the pangenome scale. Evolutionary information presented here provides a clear explanation of the issues associated with the use of protein conjugates from pili, flagella, or secretion systems as antigens for vaccine design, which exhibit high genetic variation in terms of non-synonymous substitutions in P. aeruginosa strains.

Salmonella flagellin is a potent carrier-adjuvant for peptide conjugate to induce peptide-specific antibody response in mice

As an agonist to innate immune system, Salmonella flagellin has been proven to be a potent adjuvant either admixed or genetically fused with antigens and applied to a variety of vaccines against infectious diseases. However, relatively little is known about its carrier-adjuvant effect for conjugate vaccine. Conjugation is an effective approach often used to make haptens such as some peptides and polysaccharides immunogenic and in some cases used to make poor immunogens more immunogenic. In the current study, Salmonella flagellin was tested for its carrier-adjuvant effect in a peptide conjugation. The recombinant Salmonella flagellin (rFliC) purified from Escherichia coli was firstly modified by maleimide groups, then coupled with a synthetic peptide (EXP153:CDNNLVSGP) that is a B-cell epitope derived from Plasmodium falciparum exported protein-1 to generate the conjugate of EXP153-rFliC. Bioactivity assay showed that both chemical modification and conjugation did not apparently impair the TLR5-ligand activity of rFliC. EXP153-rFliC was used to immunize BALB/c mice via subcutaneous route, and the sera obtained from immunized mice were examined by ELISA and IFA. While no detectable antibody responses were induced by the peptide admixed with rFliC, the robust peptide-specific antibody responses were observed in mice immunized with the peptide conjugated to rFliC in the absence of any additional adjuvant. The immune sera induced by the conjugate recognized the native protein of malaria parasite. The data obtained from this study demonstrate the carrier-adjuvant activity of Salmonella flagellin in peptide conjugate immunization and indicate its promising application for conjugate vaccine research and development.

Flagellin as carrier and adjuvant in cocaine vaccine development

Cocaine abuse is problematic, directly and indirectly impacting the lives of millions, and yet existing therapies are inadequate and usually ineffective. A cocaine vaccine would be a promising alternative therapeutic option, but efficacy is hampered by variable production of anticocaine antibodies. Thus, new tactics and strategies for boosting cocaine vaccine immunogenicity must be explored. Flagellin is a bacterial protein that stimulates the innate immune response via binding to extracellular Toll-like receptor 5 (TLR5) and also via interaction with intracellular NOD-like receptor C4 (NLRC4), leading to production of pro-inflammatory cytokines. Reasoning that flagellin could serve as both carrier and adjuvant, we modified recombinant flagellin protein to display a cocaine hapten termed GNE. The resulting conjugates exhibited dose-dependent stimulation of anti-GNE antibody production. Moreover, when adjuvanted with alum, but not with liposomal MPLA, GNE-FliC was found to be better than our benchmark GNE-KLH. This work represents a new avenue for exploration in the use of hapten-flagellin conjugates to elicit antihapten immune responses.

A scalable method for biochemical purification of Salmonella flagellin

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Highly purified flagellins obtained from liquid bacterial fermentation supernatants.

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Purification accomplished in four process steps to clarify, bind, wash, polish.

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Ion-exchange membranes exhibit improved flagellin retention compared to resins.

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Purified flagellins retain epitope conformation, innate immune biological activity.

Flagellins are the main structural proteins of bacterial flagella and potent stimulators of innate and adaptive immunity in mammals. The flagellins of Salmonella are virulence factors and protective antigens, and form the basis of promising vaccines. Despite broad interest in flagellins as antigens and adjuvants in vaccine formulations, there have been few advances towards the development of scalable and economical purification methods for these proteins. We report here a simple and robust strategy to purify flagellin monomers from the supernatants of liquid growth culture. Phase 1 flagellins from Salmonella enterica serovars Typhimurium (i epitope) and Enteritidis (g,m epitopes) were purified directly from conditioned fermentation growth media using sequential cation- and anion-exchange chromatography coupled with a final tangential flow-filtration step. Conventional porous chromatography resin was markedly less efficient than membrane chromatography for flagellin purification. Recovery after each process step was robust, with endotoxin, nucleic acid and residual host–cell protein effectively removed. The final yield was 200–300 mg/L fermentation culture supernatant, with ∼45–50% overall recovery. A final pH 2 treatment step was instituted to ensure uniformity of flagellin in the monomeric form. Flagellins purified by this method were recognized by monoclonal anti-flagellin antibodies and maintained capacity to activate Toll-like Receptor 5. The process described is simple, readily scalable, uses standard bioprocess methods, and requires only a few steps to obtain highly purified material.

Vaccines for Pseudomonas aeruginosa: a long and winding road

Despite the recognition of Pseudomonas aeruginosa as an opportunistic pathogen, no vaccine against this bacteria has come to market. This review describes the current state-of-the-art in vaccinology for this bacterium. This includes a discussion of those at risk for infection, the types of vaccines and the approaches for empirical and targeted antigen selection under development, as well as a perspective on where the field should go. In addition, the challenges in developing a vaccine for those individuals at risk are discussed.

9.05 Technology-Enabled Synthesis of Carbohydrates

Automated solid-phase oligosaccharide synthesis has revolutionized the emerging field of glycomics. The automation process, in which selectively functionalized monosaccharide building blocks are added sequentially to a growing oligosaccharide chain connected via an inert linker to a solid support, has been used to prepare a number of biologically relevant oligosaccharide-based constructs in record time and on scales that would have been impossible using standard solution-phase synthetic techniques. This review highlights recent developments in automated solid-phase oligosaccharide synthesis including engineering advancements that have led to the design of a fully automated platform, new and improved linker strategies that have broadened the scope of the chemical reactions that can be used in automation, and recent developments in the synthesis of functionalized monosaccharide building blocks. The automated solid-phase synthesis of biologically relevant carbohydrate constructs including bacterial and viral antigens, cancer antigens, vaccine candidates, and N-linked core oligosaccharides is also presented.

Utilizing bacterial flagellins against infectious diseases and cancers

The flagellum is the organelle providing motility to bacterial cells and its activity is coupled to the cellular chemotaxis machinery. The flagellar filament is the largest portion of the flagellum, which consists of repeating subunits of the protein flagellin. Receptors of the innate immune system including Toll like receptor 5, ICE protease activating factor, and neuronal apoptosis inhibitory protein 5 signal in response to bacterial flagellins. In addition to inducing innate immune responses, bacterial flagellins mediate the development of adaptive immune responses to both flagellins and coadministered antigens. Therefore, these proteins have intensively been investigated for the vaccine development and the immunotherapy. This review describes the utilization of bacterial flagellins for the construction of vaccines against infectious diseases and cancer immunotherapy. Furthermore, the key factors affecting the performance of these systems are highlighted.

Synthetically defined glycoprotein vaccines: current status and future directions

Primary examples in vaccine design have shown good levels of carbohydrate-specific antibody generation when raised using extracted or fully synthetic capsular polysaccharide glycans covalently coupled to a protein carrier. Herein, we cover recent clinical developments of carbohydrate-based vaccines and describe how novel cutting-edge methodology for the total synthesis of oligosaccharides and for the precise placement of carbohydrates at pre-determined sites within a protein may be used to further improve the safety and efficacy of glycovaccines.

Flagellin-PAc fusion protein is a high-efficacy anti-caries mucosal vaccine

We previously demonstrated that an anti-caries DNA vaccine intranasally administered with recombinant flagellin protein as a mucosal adjuvant enhanced salivary IgA response and conferred better protection against caries. However, the relatively weak immunogenicity of DNA vaccines and the necessity for a large quantity of antigens remain significant challenges. Here, we fused the flagellin derived from E. coli (KF) and target antigen PAc containing the A-P fragment of PAc from S. mutans (rPAc) to produce a single recombinant protein (KF-rPAc). The abilities of KF-rPAc to induce rPAc-specific mucosal and systemic responses and protective efficiency against caries following intranasal immunization were compared with those of rPAc alone or a mixture of rPAc and KF (KF + rPAc) in rats. Results showed that KF-rPAc promoted significantly higher rPAc-specific antibodies in serum as well as in saliva than did an equivalent dose of rPAc alone or a mixture of KF + rPAc. Intranasal immunization of 8.5 µg KF-rPAc could achieve 64.2% reduction of dental caries in rats. In conclusion, our study demonstrated that flagellin and PAc fusion strategy is promising for anti-caries vaccine development, and KF-rPAc could be used as an anti-caries mucosal vaccine.

ISCOMATRIX: a novel adjuvant for use in prophylactic and therapeutic vaccines against infectious diseases

The ISCOMATRIX adjuvant has antigen delivery and presentation properties as well as immunomodulatory capabilities, which combine to provide enhanced and accelerated immune responses. The responses are broad, including a range of subclasses of antibodies as well as CD4(+) and CD8(+) T-cells. A range of ISCOMATRIX vaccines (ISCOMATRIX adjuvant combined with antigen) have now been tested in clinical trials and have been shown to be generally safe and well tolerated as well as immunogenic, generating both antibody (Ab) and T-cell responses. The mechanisms by which ISCOMATRIX adjuvant facilitates its immune effects are the scope of significant study and indicate that ISCOMATRIX adjuvant (i) rapidly traffics antigen into the cytosol of multiple dendritic cell subsets, (ii) induces the induction of an array of cytokines and chemokines and (iii) links the innate and adaptive immune responses in vivo in a Toll-like-receptor-independent but MyD88-dependent manner. These data highlight the clinical utility of ISCOMATRIX adjuvant in the development of prophylactic and therapeutic vaccines for infectious disease.