Immunogenic efficacy of differently produced recombinant vaccines candidates against Pseudomonas aeruginosa infections

Pseudomonas aeruginosa: Recent Advances in Vaccine Development

Pseudomonas aeruginosa is an important opportunistic human pathogen. Using its arsenal of virulence factors and its intrinsic ability to adapt to new environments, P. aeruginosa causes a range of complicated acute and chronic infections in immunocompromised individuals. Of particular importance are burn wound infections, ventilator-associated pneumonia, and chronic infections in people with cystic fibrosis. Antibiotic resistance has rendered many of these infections challenging to treat and novel therapeutic strategies are limited. Multiple clinical studies using well-characterised virulence factors as vaccine antigens over the last 50 years have fallen short, resulting in no effective vaccination being available for clinical use. Nonetheless, progress has been made in preclinical research, namely, in the realms of antigen discovery, adjuvant use, and novel delivery systems. Herein, we briefly review the scope of P. aeruginosa clinical infections and its major important virulence factors.

Cell-free expression of the outer membrane protein OprF of Pseudomonas aeruginosa for vaccine purposes

Production of recombinant proteoliposomes containing OprF from P. aeruginosa promotes the active open conformation of the porin exposing native epitopes. These OprF proteoliposomes were used as vaccines to protect mice against a P. aeruginosa acute pulmonary infection model.

Pseudomonas aeruginosa is the second-leading cause of nosocomial infections and pneumonia in hospitals. Because of its extraordinary capacity for developing resistance to antibiotics, treating infections by Pseudomonas is becoming a challenge, lengthening hospital stays, and increasing medical costs and mortality. The outer membrane protein OprF is a well-conserved and immunogenic porin playing an important role in quorum sensing and in biofilm formation. Here, we used a bacterial cell-free expression system to reconstitute OprF under its native forms in liposomes and we demonstrated that the resulting OprF proteoliposomes can be used as a fully functional recombinant vaccine against P. aeruginosa. Remarkably, we showed that our system promotes the folding of OprF into its active open oligomerized state as well as the formation of mega-pores. Our approach thus represents an easy and efficient way for producing bacterial membrane antigens exposing native epitopes for vaccine purposes.

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.

Bioengineering a bacterial pathogen to assemble its own particulate vaccine capable of inducing cellular immunity

Many bacterial pathogens naturally form cellular inclusions. Here the immunogenicity of polyhydroxyalkanoate (PHA) inclusions and their use as particulate vaccines delivering a range of host derived antigens was assessed. Our study showed that PHA inclusions of pathogenic Pseudomonas aeruginosa are immunogenic mediating a specific cell-mediated immune response. Protein engineering of the PHA inclusion forming enzyme by translational fusion of epitopes from vaccine candidates outer membrane proteins OprI, OprF, and AlgE mediated self-assembly of PHA inclusions coated by these selected antigens. Mice vaccinated with isolated PHA inclusions produced a Th1 type immune response characterized by antigen-specific production of IFN-γ and IgG2c isotype antibodies. This cell-mediated immune response was found to be associated with the production of functional antibodies reacting with cells of various P. aeruginosa strains as well as facilitating opsonophagocytic killing. This study showed that cellular inclusions of pathogenic bacteria are immunogenic and can be engineered to display selected antigens suitable to serve as particulate subunit vaccines against infectious diseases.

A fusion protein vaccine containing OprF epitope 8, OprI, and type A and B flagellins promotes enhanced clearance of nonmucoid Pseudomonas aeruginosa. Infect Immun. 2009;77:2356-2366. [PMID: 19349426 DOI: 10.1128/iai.00054-09]

Although chronic Pseudomonas aeruginosa infection is the major cause of morbidity and mortality in cystic fibrosis (CF) patients, there is no approved vaccine for human use against P. aeruginosa. The goal of this study was to establish whether a multivalent vaccine containing P. aeruginosa type A and B flagellins as well as the outer membrane proteins OprF and OprI would promote enhanced clearance of P. aeruginosa. Intramuscular immunization with flagellins and OprI (separate) or OprI-flagellin fusion proteins generated significant antiflagellin immunoglobulin G (IgG) responses. However, only the fusions of OprI with type A and type B flagellins generated OprI-specific IgG. Immunization with a combination of OprF epitope 8 (OprF(311-341)), OprI, and flagellins elicited high-affinity IgG antibodies specific to flagellins, OprI, and OprF that individually promoted extensive deposition of C3 on P. aeruginosa. Although these antibodies exhibited potent antibody-dependent complement-mediated killing of nonmucoid bacteria, they were significantly less effective with mucoid isolates. Mice immunized with the OprF(311-341)-OprI-flagellin fusion had a significantly lower bacterial burden three days postchallenge and cleared the infection significantly faster than control mice. In addition, mice immunized with the OprF(311-341)-OprI-flagellin fusion had significantly less inflammation and lung damage throughout the infection than OprF-OprI-immunized mice. Based on our results, OprF(311-341)-OprI-flagellin fusion proteins have substantial potential as components of a vaccine against nonmucoid P. aeruginosa, which appears to be the phenotype of the bacterium that initially colonizes CF patients.

Immune responses in the airways by nasal vaccination with systemic boosting against Pseudomonas aeruginosa in chronic lung disease. Vaccine. 2009;27:2755-2759. [PMID: 19366571 DOI: 10.1016/j.vaccine.2009.03.010]

RATIONALE

Pneumonia caused by Pseudomonas (P.) aeruginosa is a leading cause of morbidity and mortality in patients with chronic lung diseases. Systemic vaccination in patients with cystic fibrosis has been only successful in part. Mucosal vaccination could lead to enhanced airway immunogenicity. Pathogen specific secretory IgA antibodies could prevent bacterial invasion into the lung mucosa.

OBJECTIVES

A phase 1-2 mucosal vaccination trial with an intranasal P. aeruginosa vaccine was performed.

METHODS

12 patients with chronic lung diseases (8 COPD, 2 cystic fibrosis, 1 bronchiectasis, 1 histiocytosis X) were vaccinated three times intranasally followed by a systemic booster vaccination with a recombinant hybrid protein encompassing the main protective epitopes of two outer membrane proteins of P. aeruginosa. Mucosal and systemic antibody responses were measured after boosting and after a half-year follow-up compared to a representative control cohort.

MEASUREMENTS

Specific IgG and IgA antibodies in the patient's sera, saliva and sputum were determined by enzyme-linked immunosorbent assay (ELISA) and IgG subclass distributions were defined with monoclonal mouse antibodies.

RESULTS

Both forms of vaccination were well tolerated. Significant elevated IgA and IgG antibodies could be measured in sputum, saliva and in the sera of 11/12 patients.

CONCLUSIONS

Mucosal vaccination followed by systemic boost with an outer membrane protein vaccine against P. aeruginosa leads to airway immunogenicity against the pathogen. Further clinical trials should elucidate the protective efficacy of this vaccination method.

NERVE: new enhanced reverse vaccinology environment

Background

Since a milestone work on Neisseria meningitidis B, Reverse Vaccinology has strongly enhanced the identification of vaccine candidates by replacing several experimental tasks using in silico prediction steps. These steps have allowed scientists to face the selection of antigens from the predicted proteome of pathogens, for which cell culture is difficult or impossible, saving time and money. However, this good example of bioinformatics-driven immunology can be further developed by improving in silico steps and implementing biologist-friendly tools.

Results

We introduce NERVE (New Enhanced Reverse Vaccinology Environment), an user-friendly software environment for the in silico identification of the best vaccine candidates from whole proteomes of bacterial pathogens. The software integrates multiple robust and well-known algorithms for protein analysis and comparison. Vaccine candidates are ranked and presented in a html table showing relevant information and links to corresponding primary data. Information concerning all proteins of the analyzed proteome is not deleted along selection steps but rather flows into an SQL database for further mining and analyses.

Conclusion

After learning from recent years' works in this field and analysing a large dataset, NERVE has been implemented and tuned as the first available tool able to rank a restricted pool (~8–9% of the whole proteome) of vaccine candidates and to show high recall (~75–80%) of known protective antigens. These vaccine candidates are required to be "safe" (taking into account autoimmunity risk) and "easy" for further experimental, high-throughput screening (avoiding possibly not soluble antigens). NERVE is expected to help save time and money in vaccine design and is available as an additional file with this manuscript; updated versions will be available at .

Yersinia pestis outer membrane type III secretion protein YscC: expression, purification, characterization, and induction of specific antiserum

The type III secretion system (YscC) protein of Yersinia pestis plays an essential role in the translocation of Yersinia outer proteins (Yops) into eukaryotic target cells through a type III secretion mechanism. To assess the immunogenicity and potential protective efficacy of YscC against lethal plague challenge, we cloned, overexpressed, and purified YscC using two different bacterial expression and purification systems. The resulting expression plasmids for YscC, pETBlue-2-YscC and pTYB11-YscC, were regulated by robust T7 promoters that were induced with isopropyl-beta-D-thiogalactopyranoside. The intein-fusion pTYB11-YscC system and the six-histidine-tagging pETBlue-2-YscC system were both successful for producing and purifying YscC. The intein-mediated purification system produced about 1mg of soluble YscC per liter of bacterial culture while the YscC-His(6)-tag method resulted in 16mg of insoluble YscC per liter of bacterial culture. Protein identity for purified YscC-His(6) was confirmed by ion trap mass spectrometry. Antisera were produced against both YscC and YscC-His(6). The specific immune response generated in YscC-vaccinated mice was relative to the particular purified protein, YscC or YscC-His(6), which was used for vaccination as determined by Western blot analysis and ELISA. Regardless of the purification method, either form of the YscC protein failed to elicit a protective immune response against lethal plague challenge with either F1 capsule forming Y. pestis CO92 or the isogenic F1(-)Y. pestis C12.

Recombinant OprF-OprI as a vaccine against Pseudomonas aeruginosa infections

A vaccine against Pseudomonas aeruginosa based on recombinant outer membranes has been developed. After intramuscularly injecting into patients with severe burns, antibodies against P. aeruginosa were induced. Vaccination was well tolerated. Intranasal application of the vaccine into volunteers, induced specific s-IgA antibodies. We conclude that the newly developed vaccine may be suitable for protection of the main risk groups of P. aeruginosa infections. In particular, for the protection of burn patients and patients with cystic fibrosis.