Protection of immunocompromised mice against lethal infection with Pseudomonas aeruginosa by active or passive immunization with recombinant P. aeruginosa outer membrane protein F and outer membrane protein I fusion proteins

Anti-Pseudomonas aeruginosa Vaccines and Therapies: An Assessment of Clinical Trials

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that causes high morbidity and mortality in cystic fibrosis (CF) and immunocompromised patients, including patients with ventilator-associated pneumonia (VAP), severely burned patients, and patients with surgical wounds. Due to the intrinsic and extrinsic antibiotic resistance mechanisms, the ability to produce several cell-associated and extracellular virulence factors, and the capacity to adapt to several environmental conditions, eradicating P. aeruginosa within infected patients is difficult. Pseudomonas aeruginosa is one of the six multi-drug-resistant pathogens (ESKAPE) considered by the World Health Organization (WHO) as an entire group for which the development of novel antibiotics is urgently needed. In the United States (US) and within the last several years, P. aeruginosa caused 27% of deaths and approximately USD 767 million annually in health-care costs. Several P. aeruginosa therapies, including new antimicrobial agents, derivatives of existing antibiotics, novel antimicrobial agents such as bacteriophages and their chelators, potential vaccines targeting specific virulence factors, and immunotherapies have been developed. Within the last 2-3 decades, the efficacy of these different treatments was tested in clinical and preclinical trials. Despite these trials, no P. aeruginosa treatment is currently approved or available. In this review, we examined several of these clinicals, specifically those designed to combat P. aeruginosa infections in CF patients, patients with P. aeruginosa VAP, and P. aeruginosa-infected burn patients.

Nanotoxoid vaccination protects against opportunistic bacterial infections arising from immunodeficiency

The rise in nosocomial infections caused by multidrug-resistant pathogens is a major public health concern. Patients taking immunosuppressants or chemotherapeutics are naturally more susceptible to infections. Thus, strategies for protecting immunodeficient individuals from infections are of great importance. Here, we investigate the effectiveness of a biomimetic nanotoxoid vaccine in defending animals with immunodeficiency against Pseudomonas aeruginosa. The nanotoxoids use a macrophage membrane coating to sequester and safely present bacterial virulence factors that would otherwise be too toxic to administer. Vaccination with the nanoformulation results in rapid and long-lasting immunity, protecting against lethal infections despite severe immunodeficiency. The nanovaccine can be administered through multiple routes and is effective in both pneumonia and septicemia models of infection. Mechanistically, protection is mediated by neutrophils and pathogen-specific antibodies. Overall, nanotoxoid vaccination is an attractive strategy to protect vulnerable patients and could help to mitigate the threat posed by antibiotic-resistant superbugs.

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.

Modulation of host cellular responses by gram-negative bacterial porins

The outer membrane of a gram-negative bacteria encapsulates the plasma membrane thereby protecting it from the harsh external environment. This membrane acts as a sieving barrier due to the presence of special membrane-spanning proteins called "porins." These porins are β-barrel channel proteins that allow the passive transport of hydrophilic molecules and are impermeable to large and charged molecules. Many porins form trimers in the outer membrane. They are abundantly present on the bacterial surface and therefore play various significant roles in the host-bacteria interactions. These include the roles of porins in the adhesion and virulence mechanisms necessary for the pathogenesis, along with providing resistance to the bacteria against the antimicrobial substances. They also act as the receptors for phage and complement proteins and are involved in modulating the host cellular responses. In addition, the potential use of porins as adjuvants, vaccine candidates, therapeutic targets, and biomarkers is now being exploited. In this review, we focus briefly on the structure of the porins along with their important functions and roles in the host-bacteria interactions.

Bioinformatics analyses for the designation of a hybrid protein against urinary tract infections caused by Pseudomonas aeruginosa and investigation of the presence of pre-existing antibodies in infected humans

Pseudomonas aeruginosa is an important pathogen causing urinary tract infections (UTIs) and resistance to antibiotics has increased the need for a vaccine against this bacterium. P. aeruginosa V-antigen (PcrV), which is a component of the type III secretion system, delivers exoenzymes such as exoenzyme S (ExoS) into the host cells. In the present study, we aimed to design and express a hybrid protein composed of PcrV and ExoS from P. aeruginosa using bioinformatics. Finally, pre-existing antibodies were evaluated in sera collected from patients with UTI. The prediction results showed that the hybrid protein ExoS.PcrV had a C-score of -0.85 and Z-score of -5.55 versus C-score of -2.93 and Z-score of -2.65 for PcrV.ExoS. Based on BepiPred and ABCpred, 15 and 14 linear B-cell epitopes, as well as five conformational epitopes were identified in ExoS.PcrV. The interaction between the protein and immune receptor was validated in silico. Molecular docking indicated that the hybrid protein interacted strongly with Toll-like receptor 2. ExoS.PcrV was expressed in pET28a-BL21 and purified with a size of 57 kD by Nickel resins. The protein reacted with all sera collected from humans infected with P. aeruginosa following Western blot. The infected patients produced significantly higher IgG levels against the protein compared to the control as indicated by ELISA. The protein ExoS.PcrV was determined as a promising candidate against UTI caused by P. aeruginosa and the presence of pre-existing antibodies indicated the advantage of the hybrid protein. Evaluation of the efficacy of hybrid protein is ongoing in mice model. Communicated by Ramaswamy H. Sarma.

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.

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.

How to kill Pseudomonas-emerging therapies for a challenging pathogen

As the number of effective antibiotics dwindled, antibiotic resistance (AR) became a pressing concern. Some Pseudomonas aeruginosa isolates are resistant to all available antibiotics. In this review, we identify the mechanisms that P. aeruginosa uses to evade antibiotics, including intrinsic, acquired, and adaptive resistance. Our review summarizes many different approaches to overcome resistance. Antimicrobial peptides have potential as therapeutics with low levels of resistance evolution. Rationally designed bacteriophage therapy can circumvent and direct evolution of AR and virulence. Vaccines and monoclonal antibodies are highlighted as immune-based treatments targeting specific P. aeruginosa antigens. This review also identifies promising drug combinations, antivirulence therapies, and considerations for new antipseudomonal discovery. Finally, we provide an update on the clinical pipeline for antipseudomonal therapies and recommend future avenues for research.

Defining the Mechanistic Correlates of Protection Conferred by Whole-Cell Vaccination against Pseudomonas aeruginosa Acute Murine Pneumonia

Pseudomonas aeruginosa is a Gram-negative pathogen that causes severe pulmonary infections associated with high morbidity and mortality in immunocompromised patients. The development of a vaccine against P. aeruginosa could help prevent infections caused by this highly antibiotic-resistant microorganism.

Pseudomonas aeruginosa is a Gram-negative pathogen that causes severe pulmonary infections associated with high morbidity and mortality in immunocompromised patients. The development of a vaccine against P. aeruginosa could help prevent infections caused by this highly antibiotic-resistant microorganism. We propose that identifying the vaccine-induced correlates of protection against P. aeruginosa will facilitate the development of a vaccine against this pathogen. In this study, we investigated the mechanistic correlates of protection of a curdlan-adjuvanted P. aeruginosa whole-cell vaccine (WCV) delivered intranasally. The WCV significantly decreased bacterial loads in the respiratory tract after intranasal P. aeruginosa challenge and raised antigen-specific antibody titers. To study the role of B and T cells during vaccination, anti-CD4, -CD8, and -CD20 depletions were performed prior to WCV vaccination and boosting. The depletion of CD4⁺, CD8⁺, or CD20⁺ cells had no impact on the bacterial burden in mock-vaccinated animals. However, depletion of CD20⁺ B cells, but not CD8⁺ or CD4⁺ T cells, led to the loss of vaccine-mediated bacterial clearance. Also, passive immunization with serum from WCV group mice alone protected naive mice against P. aeruginosa, supporting the role of antibodies in clearing P. aeruginosa. We observed that in the absence of T cell-dependent antibody production, mice vaccinated with the WCV were still able to reduce bacterial loads. Our results collectively highlight the importance of the humoral immune response for protection against P. aeruginosa and suggest that the production of T cell-independent antibodies may be sufficient for bacterial clearance induced by whole-cell P. aeruginosa vaccination.

Oligomerization of IC43 resulted in improved immunogenicity and protective efficacy against Pseudomonas aeruginosa lung infection

IC43, a truncate form of outer membrane proteins OprF_190-342 and OprI_21-83 from Pseudomonas aeruginosa, is a promising candidate antigen and exists as monomer in solution. In this study, we generated the heptamer of IC43 by carrier protein aided oligomerization, which was confirmed by gel-filtration and chemical cross-linking analysis. The carrier protein naturally exists as a homo-heptamer, and IC43 was displayed on the surface of the carrier protein in the fusion protein. Immunization with this fusion protein resulted in increased level of antigen specific IgG antibodies and higher survival rate after infection. The improved efficacy was correlated with lower bacteria burden, inflammation and tissue damage in the lungs of immunized mice. Further studies revealed that immunization with this fusion protein resulted in increased levels of IL-4 and antigen specific IgG1, suggesting a stronger Th2 immune response was induced. The improved immunogenicity may be attributed to the exposure of more epitopes on the antigen, which was confirmed by results from immune-dominant peptide mapping and passive immunization. These results demonstrated a possible strategy to improve the immunogenicity of an antigen by carrier protein aided oligomerization.

A Live Salmonella Vaccine Delivering PcrV through the Type III Secretion System Protects against Pseudomonas aeruginosa

The Gram-negative bacterium Pseudomonas aeruginosa is an important opportunistic pathogen that causes infections in cystic fibrosis and hospitalized patients. Therapeutic treatments are limited due to the emergence and spread of new antibiotic-resistant strains. In this context, the development of a vaccine is a priority. Here, we used an attenuated strain of Salmonella enterica serovar Typhimurium as a vehicle to express and deliver the Pseudomonas antigen PcrV. This vaccine induced the generation of specific antibodies in mice and protected them from lethal infections with P. aeruginosa. This is an important step toward the development of an effective vaccine for the prevention of infections caused by P. aeruginosa in humans.

Pseudomonas aeruginosa is a common Gram-negative opportunistic pathogen that is intrinsically resistant to a wide range of antibiotics. The development of a broadly protective vaccine against P. aeruginosa remains a major challenge. Here, we used an attenuated strain of Salmonella enterica serovar Typhimurium as a vehicle to express P. aeruginosa antigens. A fusion between the S. enterica type III secretion effector protein SseJ and the P. aeruginosa antigen PcrV expressed under the control of the sseA promoter was translocated by Salmonella into host cells in vitro and elicited the generation of specific antibodies in mice. Mice immunized with attenuated Salmonella expressing this fusion had reduced bacterial loads in the spleens and lungs and lower serum levels of proinflammatory cytokines than control mice after P. aeruginosa infection. Importantly, immunized mice also showed significantly enhanced survival in this model. These results suggest that type III secretion effectors of S. enterica are appropriate carriers in the design of a live vaccine to prevent infections caused by P. aeruginosa.

IMPORTANCE The Gram-negative bacterium Pseudomonas aeruginosa is an important opportunistic pathogen that causes infections in cystic fibrosis and hospitalized patients. Therapeutic treatments are limited due to the emergence and spread of new antibiotic-resistant strains. In this context, the development of a vaccine is a priority. Here, we used an attenuated strain of Salmonella enterica serovar Typhimurium as a vehicle to express and deliver the Pseudomonas antigen PcrV. This vaccine induced the generation of specific antibodies in mice and protected them from lethal infections with P. aeruginosa. This is an important step toward the development of an effective vaccine for the prevention of infections caused by P. aeruginosa in humans.

Genome-Based Approach Delivers Vaccine Candidates Against Pseudomonas aeruginosa

High incidence, severity and increasing antibiotic resistance characterize Pseudomonas aeruginosa infections, highlighting the need for new therapeutic options. Vaccination strategies to prevent or limit P. aeruginosa infections represent a rational approach to positively impact the clinical outcome of risk patients; nevertheless this bacterium remains a challenging vaccine target. To identify novel vaccine candidates, we started from the genome sequence analysis of the P. aeruginosa reference strain PAO1 exploring the reverse vaccinology approach integrated with additional bioinformatic tools. The bioinformatic approaches resulted in the selection of 52 potential antigens. These vaccine candidates were conserved in P. aeruginosa genomes from different origin and among strains isolated longitudinally from cystic fibrosis patients. To assess the immune-protection of single or antigens combination against P. aeruginosa infection, a vaccination protocol was established in murine model of acute respiratory infection. Combinations of selected candidates, rather than single antigens, effectively controlled P. aeruginosa infection in the in vivo model of murine pneumonia. Five combinations were capable of significantly increase survival rate among challenged mice and all included PA5340, a hypothetical protein exclusively present in P. aeruginosa. PA5340 combined with PA3526-MotY gave the maximum protection. Both proteins were surface exposed by immunofluorescence and triggered a specific immune response. Combination of these two protein antigens could represent a potential vaccine to prevent P. aeruginosa infection.

Escherichia coli outer membrane protein F (OmpF): an immunogenic protein induces cross-reactive antibodies against Escherichia coli and Shigella

Diarrhea caused by pathogenic Escherichia coli (E. coli) is one of the most serious infectious diseases in humans and animals. Due to antibiotics resistance and the lack of efficient vaccine, more attention should be paid to find potential versatile vaccine candidates to prevent diseases. In this study, the sequence homology analysis indicated that OmpF from E. coli CVCC 1515 shares a high identity (90−100%) with about half of the E. coli (46.7%) and Shigella (52.8%) strains. Then the recombinant OmpF was supposed to be developed as a versatile vaccine to prevent E. coli infection. OmpF was expressed in E. coli BL21 (DE3) using the auto-induction method. The recombinant OmpF (rOmpF) protein had an average molecular weight of 40 kDa with the purity of 90%. Immunological analysis indicated that the titers of anti-rOmpF sera against rOmpF and whole cells were 1:240,000 and 1:27,000, respectively. The opsonophagocytosis result showed that 72.21 ± 11.39 and 11.04 ± 3.90% of bacteria were killed in the rOmpF immunization and control groups, respectively. The survival ratio of mice immunized with rOmpF ranged between 40 and 60% as observed within 36 h after challenge, indicating mice were partially protected from E. coli CVCC 1515 infection. The expressed rOmpF protein induced an effective immune response, but only provide a weak protection against pathogenic E. coli CVCC 1515 and a small reduction in E. coli CICC 21530 (O157:H7) excretion in a mouse infection model. Native forms of the OmpF antigen may be studied for immunogenicity and potential protective efficacy.

Immunization with outer membrane proteins (OprF and OprI) and flagellin B protects mice from pulmonary infection with mucoid and nonmucoid Pseudomonas aeruginosa

BACKGROUND

Pseudomonas aeruginosa is a Gram-negative opportunistic bacterium, which considered as a common cause of nosocomial infection and life-threatening complications in immunocompromized and cystic fibrosis patients. Here, we evaluate the protective effect of recombinant vaccines composed of outer membrane proteins OprF and OprI alone or in combination with flagellin B against mucoid and nonmucoid pseudomonas infection.

METHODS

BALB/C mice were immunized subcutaneous using OprF and OprI with or without flagellin B and antibody titers were determined. Serum bactericidal and opsonophagocytosis activities of immunized and control sera were estimated against mucoid and nonmucoid pseudomonas strains. Lung tissue sections from immunized and nonimmunized mice were analyzed and the levels of peripheral neutrophils infiltration into the lung and tissue inflammation were scored.

RESULTS

Subcutaneous immunization using OprF and OprI with or without flagellin B elicited higher antibody titers against OprF, OprI, and flagellin B. The produced antibodies successfully opsonized both mucoid and nonmucoid strains with subsequent activation of the terminal pathway of complement that enhances killing of nonmucoid strains via complement-mediated lysis. Furthermore, opsonized mucoid and nonmucoid strains showed enhanced opsonophagocytosis via human peripheral neutrophils, a mechanism that kills P. aeruginosa when complement mediated lysis is not effective especially with mucoid strains. Immunized mice also showed a significant prolonged survival time, lower bacteremia, and reduced lung damage when compared with control nonimmunized mice.

CONCLUSION

Our data showed that mice immunized with OprF/OprI or OprF/OprI and flagellin B are significantly protected from infection caused by mucoid and nonmucoid strains of P. aeruginosa.

Pseudomonas aeruginosa ventilator-associated pneumonia management

Ventilator-associated pneumonia is the most common infection in intensive care unit patients associated with high morbidity rates and elevated economic costs; Pseudomonas aeruginosa is one of the most frequent bacteria linked with this entity, with a high attributable mortality despite adequate treatment that is increased in the presence of multiresistant strains, a situation that is becoming more common in intensive care units. In this manuscript, we review the current management of ventilator-associated pneumonia due to P. aeruginosa, the most recent antipseudomonal agents, and new adjunctive therapies that are shifting the way we treat these infections. We support early initiation of broad-spectrum antipseudomonal antibiotics in present, followed by culture-guided monotherapy de-escalation when susceptibilities are available. Future management should be directed at blocking virulence; the role of alternative strategies such as new antibiotics, nebulized treatments, and vaccines is promising.

Mannose-modified chitosan microspheres enhance OprF-OprI-mediated protection of mice against Pseudomonas aeruginosa infection via induction of mucosal immunity

Pseudomonas aeruginosa is an opportunistic pathogen that localizes to and colonizes mucosal tissue. Thus, vaccines that elicit a strong mucosal response against P. aeruginosa should be superior to other vaccination strategies. In this study, to stimulate rapid and enhanced mucosal immune responses, mannose-modified chitosan microspheres loaded with the recombinant outer membrane protein OprF190-342-OprI21-83 (FI) (FI-MCS-MPs) of P. aeruginosa were developed as a potent subunit vaccine for mucosal delivery. FI-MCS-MPs were successfully obtained via the tripolyphosphate ionic crosslinking method. Confocal and immunohistochemical analyses indicated that FI-MCS-MPs exhibited the ability to bind the macrophage mannose receptor (MMR, CD206) in vitro and in vivo. After intranasal immunization of mice with FI-MCS-MPs, FI-specific humoral immune responses were detected, measured as local IgM antibody titers in lung tissue slurry; IgA antibody titers in nasal washes, bronchoalveolar lavage (BAL), and intestinal lavage; and systemic IgA and IgG antibody titers in serum. FI-MCS-MPs induced early and high mucosal and systemic humoral antibody responses comparable to those in the group vaccinated with unmodified mannose. High levels of IFN-γ and IL-4 in addition to T lymphocyte subsets induced a mixed Th1/Th2 response in mice immunized with FI-MCS-MPs, resulting in the establishment of cellular immunity. Additionally, when immunized mice were challenged with P. aeruginosa via the nasal cavity, FI-MCS-MPs demonstrated 75 % protective efficacy. Together, these data indicate that mannose-modified chitosan microspheres are a promising subunit delivery system for vaccines against P. aeruginosa infection.

Vaccine protection of leukopenic mice against Staphylococcus aureus bloodstream infection

The risk for Staphylococcus aureus bloodstream infection (BSI) is increased in immunocompromised individuals, including patients with hematologic malignancy and/or chemotherapy. Due to the emergence of antibiotic-resistant strains, designated methicillin-resistant S. aureus (MRSA), staphylococcal BSI in cancer patients is associated with high mortality; however, neither a protective vaccine nor pathogen-specific immunotherapy is currently available. Here, we modeled staphylococcal BSI in leukopenic CD-1 mice that had been treated with cyclophosphamide, a drug for leukemia and lymphoma patients. Cyclophosphamide-treated mice were highly sensitive to S. aureus BSI and developed infectious lesions lacking immune cell infiltrates. Virulence factors of S. aureus that are key for disease establishment in immunocompetent hosts-α-hemolysin (Hla), iron-regulated surface determinants (IsdA and IsdB), coagulase (Coa), and von Willebrand factor binding protein (vWbp)-are dispensable for the pathogenesis of BSI in leukopenic mice. In contrast, sortase A mutants, which cannot assemble surface proteins, display delayed time to death and increased survival in this model. A vaccine with four surface antigens (ClfA, FnBPB, SdrD, and SpAKKAA), which was identified by genetic vaccinology using sortase A mutants, raised antigen-specific immune responses that protected leukopenic mice against staphylococcal BSI.

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.

Vaccination efficiency of surface antigens and killed whole cell of Pseudomonas putida in large yellow croaker (Pseudosciaena crocea)

Large yellow croaker (Pseudosciaena crocea), a major marine fish aquacultured in the southeastern coastal region of China, has become endangered by the pathogen Pseudomonas putida in recent years. P. putida infections occur in low water temperatures when fish reduce food intake, thus oral antibiotic administration is not practical. Therefore, vaccination may be the only method to prevent the infection. In the present study, main surface antigens of P. putida, including lipopolysaccharide (LPS), outer membrane proteins (OMP), extracellular biofilm polysaccharide (EPS), and formalin-killed cell (FKC) bacterin, were prepared and the fish vaccinated. On post-immunization day 28, serum antibody titers, phagocytic responses of leukocytes, and lysozyme activities of the fish were evaluated. The efficiency of vaccination was tested by artificial challenge via intraperitoneal injection of live bacteria on post-immunization day 28 and 35, respectively. The results showed that although significant humoral and innate immune responses were elicited in all vaccination groups, the challenge produced similar poor protection in both tests, with a relative percent survival (RPS) of 0-40%. Although the EPS group showed a complete lack of protection, LPS reached the highest RPS value (40%), suggesting that LPS may be involved in protection immunity against the pathogen. Further analysis of the ultra-structures of tissues from infected fish via TEM revealed macrophage survival and intracellular replication ability of the pathogen. New strategies for development might put more emphasis on efficient clearance of intracellular bacteria. The present study is the first to report vaccination against the fish pathogen P. putida and the first investigation of intracellular survival of this pathogen in host macrophages.

Identification of immunogenic proteins within distinct molecular mass fractions of Flavobacterium psychrophilum

Flavobacterium psychrophilum is the aetiological agent of bacterial coldwater disease (CWD), and this pathogen has large economic impacts on salmonid aquaculture worldwide. Previously, it was demonstrated that high levels of protection against F. psychrophilum challenge were conferred to rainbow trout, Oncorhynchus mykiss (Walbaum), by immunization with distinct molecular mass fractions of the bacterium, and specific antibodies were correlated with protection. In this study, an immunoproteomic analysis of F. psychrophilum was performed using two-dimensional polyacrylamide gel electrophoresis and Western blotting with serum from fish immunized with high- and mid-molecular mass fractions of the bacterium. Mass spectrometry was used to determine the protein identity, and 15 immunogenic proteins were positively identified following Mascot searches of the F. psychrophilum genome. Based on known function and immunogenicity of homologous proteins in other bacterial pathogens, antibodies specific for several of the identified proteins may be important for protective immunity from CWD. These include outer membrane protein OmpA (P60), trigger factor, ClpB, elongation factor G, gliding motility protein GldN and a conserved hypothetical protein. This work increases the understanding of the protective humoral immune response of rainbow trout against these distinct molecular mass fractions of F. psychrophilum and provides new potential targets for recombinant protein vaccine development.

Recent developments for Pseudomonas vaccines

Infections with Pseudomonas aeruginosa are a major health problem for immune-compromised patients and individuals with cystic fibrosis. A vaccine against: P. aeruginosa has long been sought after, but is so far not available. Several vaccine candidates have been assessed in experimental animals and humans, which include sub-cellular fractions, capsule components, purified and recombinant proteins. Unique characteristics of the host and the pathogen have complicated the vaccine development. This review summarizes the current state of vaccine development for this ubiquitous pathogen, in particular to provide mucosal immunity against infections of the respiratory tract in susceptible individuals with cystic fibrosis.

Mucosal vaccination with a multivalent, live-attenuated vaccine induces multifactorial immunity against Pseudomonas aeruginosa acute lung infection

Many animal studies investigating adaptive immune effectors important for protection against Pseudomonas aeruginosa have implicated opsonic antibody to the antigenically variable lipopolysaccharide (LPS) O antigens as a primary effector. However, active and passive vaccination of humans against these antigens has not shown clinical efficacy. We hypothesized that optimal immunity would require inducing multiple immune effectors targeting multiple bacterial antigens. Therefore, we evaluated a multivalent live-attenuated mucosal vaccination strategy in a murine model of acute P. aeruginosa pneumonia to assess the contributions to protective efficacy of various bacterial antigens and host immune effectors. Vaccines combining 3 or 4 attenuated strains having different LPS serogroups were associated with the highest protective efficacy compared to vaccines with fewer components. Levels of opsonophagocytic antibodies, which were directed not only to the LPS O antigens but also to the LPS core and surface proteins, correlated with protective immunity. The multivalent live-attenuated vaccines overcame prior problems involving immunologic interference in the development of O-antigen-specific antibody responses when closely related O antigens were combined in multivalent vaccines. Antibodies to the LPS core were associated with in vitro killing and in vivo protection against strains with O antigens not expressed by the vaccine strains, whereas antibodies to the LPS core and surface proteins augmented the contribution of O-antigen-specific antibodies elicited by vaccine strains containing a homologous O antigen. Local CD4 T cells in the lung also contributed to vaccine-based protection when opsonophagocytic antibodies to the challenge strain were absent. Thus, multivalent live-attenuated vaccines elicit multifactorial protective immunity to P. aeruginosa lung infections.

OprF/I-vaccinated sera inhibit binding of human interferon-gamma to Pseudomonas aeruginosa

The recombinant outer membrane protein OprF/I has been demonstrated in previous studies to protect against Pseudomonas aeruginosa infection through a mechanism of enhanced antibody-mediated opsonophagocytosis. Recent evidence indicates that P. aeruginosa enhances its virulence phenotype as a consequence of binding to human IFN-gamma through an outer membrane protein, OprF. In this study, we demonstrate that a single boost injection of OprF/I vaccine elicited a strong OprF/I-specific antibody response in individuals who were previously vaccinated with OprF/I in a clinical trial. The OprF/I-vaccinated sera inhibit P. aeruginosa binding to IFN-gamma, suggesting an alternative mechanism by which the OprF/I vaccine confers protection against P. aeruginosa infection.

Protection against Pseudomonas aeruginosa lung infection in mice by recombinant OprF-pulsed dendritic cell immunization

BACKGROUND

The Pseudomonas aeruginosa major constitutive outer membrane porin protein F (OprF) has been shown to be a protective antigen and was previously used to activate an immunological response in a mouse model of lung pneumonia. The purpose of our study was to demonstrate the ability of mouse dendritic cells pulsed with purified or recombinant OprF to protect mice against P. aeruginosa infection and inflammation.Both native (n-OprF), isolated and purified from PAO1 bacterial strain, and recombinant (histidin-conjugated) OprF (His-OprF), obtained by cloning of the oprF gene into the pET28a expression vector, were used to stimulate dendritic cells in vitro before adoptive transfer into prospective recipient mice with P. aeruginosa pulmonary infection.

RESULTS

Similar to n-OprF, His-OprF activated dendritic cells in vitro, inducing the costimulatory molecule expression as well as cytokine production. Upon adoptive transfer in vivo, porin-pulsed dendritic cells (DCs) induced Th1-mediated resistance to infection and associated inflammatory pathology caused by either the PAO1 strain or a clinically-isolated mucoid strain.

CONCLUSIONS

This study highlights the pivotal contribution of DCs to vaccine-induced protection against P. aeruginosa infection and associated inflammation.

LPS-based conjugate vaccines composed of saccharide antigens of smooth-type Salmonella enteritidis and rough-type S. gallinarum 9R bound to bovine serum albumin

Lipopolysaccahrides (LPSs) from Salmonella enteritidis, S. gallinarum, and S. enterica Typhimurium showed an identical electrophoretic banding pattern and serological cross-reactions among each other. LPSs from wild-type Salmonella enteritidis and rough mutant S. gallinarum 9R were detoxified by cleavage of lipid A moieties using mild acid hydrolysis. The non-toxic saccharide moieties from both strains were coupled directly to bovine serum albumin (BSA). The conjugates were injected in mice in combination with monophosphory lipid A (MPL), Freund, and Alum adjuvants. The highest IgM and IgG titres were obtained when the conjugates were emulsified with MPL adjuvant, followed by Freund adjuvant. The antisera raised against the conjugates in combination with MPL and Freund adjuvants showed high complement-mediated lysis to the homologous strains. A correlation was observed between IgG titres and bactericidal activities against homologous strains. Low in vivo protection was obtained when mice immunized with the conjugates were challenged with 10 times the LD50 of the wild S. enteritidis.

A fusion protein vaccine containing OprF epitope 8, OprI, and type A and B flagellins promotes enhanced clearance of nonmucoid Pseudomonas aeruginosa

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

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.

Vaccination against Pseudomonas aeruginosa pneumonia in immunocompromised mice

Immunocompromised patients are highly susceptible to infection with Pseudomonas aeruginosa. Our laboratory previously showed that intranasal administration of an attenuated Salmonella strain expressing the P. aeruginosa lipopolysaccharide O antigen was effective in clearing bacteria and preventing mortality in wild-type mice after intranasal challenge. We were interested in investigating the efficacy of this vaccine strategy in immunocompromised mice. Mice rendered leukopenic or neutropenic by intraperitoneal treatment with cyclophosphamide (Cy) or RB6-8C5 antibody, respectively, were more susceptible to P. aeruginosa pneumonia than their nontreated counterparts, demonstrating 50% lethal doses several logs lower than that in wild-type mice. This hypersusceptiblity was also associated with bacterial dissemination to the liver and spleen and increased lung permeability in Cy mice. Vaccination of the mice prior to treatment resulted in better survival and lower bacterial loads compared to vector-immunized mice. Although the treatments had no effect on antibody titers, this level of protection was still lower than that seen in untreated vaccinated mice. Administration of antibodies directly to the site of infection at the time of bacterial delivery prolonged survival and lowered bacterial loads in the immunocompromised mice. These results demonstrate the importance of white blood cells while still suggesting a critical role for antibodies in protection against P. aeruginosa infection.

Application of vaccine technology to prevention of Pseudomonas aeruginosa infections

Development of an effective vaccine against the multiple presentations of Pseudomonas aeruginosa infection, including nosocomial pneumonia, bloodstream infections, chronic lung infections in cystic fibrosis patients and potentially sight-threatening keratitis in users of contact lenses, is a high priority. As with vaccine development for any pathogen, key information about the most effective immunologic effectors of immunity and target antigens needs to be established. For P. aeruginosa, although there is a role for cell-mediated immunity in animals following active vaccination, the bulk of the data indicate that opsonically-active antibodies provide the most effective mediators of acquired immunity. Major target antigens include the lipopolysaccharide O-polysaccharides, cell-surface alginate, flagella, components of the Type III secretion apparatus and outer membrane proteins with a potentially additive effect achieved by including immune effectors to toxins and proteases. A variety of active vaccination approaches have the potential for efficacy such as vaccination with purified or recombinant antigens incorporating multiple epitopes, conjugate vaccines incorporating proteins and carbohydrate antigens, and live attenuated vaccines, including heterologous antigen delivery systems expressing immunogenic P. aeruginosa antigens. A diverse range of passive immunotherapeutic approaches are also candidates for effective immunity, with a variety of human monoclonal antibodies described over the years with good preclinical efficacy and some early Phase I and II studies in humans. Finding an effective active and/or passive vaccination strategy for P. aeruginosa infections could be realized in the next 5 to 10 years, but will require that advances are made in the understanding of antigen expression and immune effectors that work in different human tissues and clinical settings, and also require a means to validate that clinical outcomes achieved in Phase III trials represent meaningful advances in management and treatment of P. aeruginosa infections.

Multivalent DNA vaccine protects mice against pulmonary infection caused by Pseudomonas aeruginosa

For efficacious vaccine development against Pseudomonas aeruginosa (P. aeruginosa), the immunogenicity of multivalent DNA vaccine was evaluated. Three different plasmids each targeting a fusion of outer membrane proteins (OprF/OprI), a protein regulating type III secretion system (PcrV), or an appendage (PilA) were prepared and mice were immunized with single (monovalent) or a combination of these plasmids (multivalent) via intramuscular electroporation (imEPT) or gene gun. Immunization with multivalent DNA vaccine via imEPT induced the most potent protection against lethal pneumonia. Although the serum levels of IgG binding to whole bacteria cells were comparable between groups, the strongest immune protection was associated with the serum levels of Th1-dominated multivalent IgG, the bronchoalveolar levels of macrophage inflammatory protein 2 (MIP-2) and IFN-gamma, and the number of neutrophils and macrophages in the bronchoalveolar lavage following intranasal challenge. These results implied the possible clinical application of multivalent DNA vaccine against P. aeruginosa.

Molecular evolution of the major outer-membrane protein gene (oprF) of Pseudomonas

The major outer-membrane protein of Pseudomonas, OprF, is multifunctional. It is a non-specific porin that plays a role in maintenance of cell shape, in growth in a low-osmolarity environment, and in adhesion to various supports or molecules. OprF has been studied extensively for its utility as a vaccine component, its role in antimicrobial drug resistance, and its porin function. The authors have previously shown important differences between the OprF and 16S rDNA phylogenies: Pseudomonas fluorescens isolates split into two quite separate clusters, probably according to their ecological niche. In this study, the evolutionary history of the oprF gene was investigated further. The study of G+C content at the third codon position, synonymous codon usage (codon adaptation index, CAI) and genomic context showed no evidence of horizontal transfer or gene duplication. Similarly, a robust likelihood test of incongruence showed no significant incongruence between the oprF phylogeny and the species phylogeny. In addition, the ratio of nonsynonymous mutations to synonymous mutations (K(a)/K(s)) is high between the different clusters, especially between the two clusters containing P. fluorescens isolates, highlighting important modifications in evolutionary constraints during the history of the oprF gene. Since OprF is known as a pleiotropic protein, modifications in evolutionary constraints could have resulted from variations in cryptic functions, correlated with the ecological fingerprint. Finally, relaxed constraints and/or episodic positive evolution, especially for some P. fluorescens strains, could have led to a phylogeny reconstruction artifact.

Safety and immunogenicity of an oral inactivated whole-cell pseudomonas aeruginosa vaccine administered to healthy human subjects

This study examines the safety and immunogenicity of an oral, whole-cell Pseudomonas aeruginosa vaccine administered to healthy volunteers. Thirty subjects received an oral dose of Pseudostat in two timed, measured doses with serological follow-up to 56 days postvaccination. Following vaccination, several individuals were identified as antibody responders for all three immunoglobulin (Ig) isotypes tested, specifically against whole-cell P. aeruginosa extract and outer membrane proteins F and I. The mean pooled lipopolysaccharide antigen-specific IgA showed the most significant and constant increases in titer postdose, with a similar increase in titer for whole-cell P. aeruginosa extract-specific IgA. The results demonstrated an increased phagocytic ability of the selected macrophage cell line in post vaccination sera. Furthermore a significant increase in intracellular macrophage killing of opsonized P. aeruginosa was also demonstrated (82% on day 14 postdose) in the presence of the postvaccination sera. The safety component of the study did not show any vaccine-attributable adverse effects in any of the subjects, as documented by clinical evidence, hematology, and biochemistry profiles. We conclude that Pseudostat is safe and immunogenic in humans at this dose and that further studies to determine the appropriate dosage and efficacy are needed. In our study, we have shown that the most significant and sustained responses to oral vaccination in human adult volunteers were serum IgA levels and that pooled sera collected postimmunization have an increased capacity to promote opsonophagocytotic killing of P. aeruginosa.

Effect of anti-OprF-OprI immunoglobulin on APACHE II score in a porcine two-hit model of hemorrhagic shock/resuscitation and pseudomonas aeruginosa sepsis

BACKGROUND

Up to now, randomized clinical trials of treatment of bacterial sepsis with immunoglobulins show conflicting results. This paper investigates the effect of prophylactic immunization with anti-OprF-OprI antiserum on the APACHE II score in a clinically relevant two-hit model of hemorrhagic shock/resuscitation followed by Pseudomonas aeruginosa sepsis in pigs.

METHODS

Twenty-three German Landrace-Hybrid pigs underwent chronic implantation of vascular catheters (internal and external jugular vein, carotic and pulmonary artery), hemorrhagic shock (mean blood loss 40% of estimated blood volume) for 45 min, followed by resuscitation with crystalloid, colloid, and shed blood. Randomization was to a control group (no immunization, n=6), an F-I group (50 mg/kg i.p. anti-OprF-OprI immunoglobulin, n=6), an S group (50 mg/kg i.p. unspecific porcine immunoglobulins, n=6), and a PS group (50 mg/kg i.p. immunoglobulin against the antigens of heat-killed P. aeruginosa, n=5). After at least 18 h for recovery from anesthesia, the pigs underwent a continuous intravenous infusion of P. aeruginosa for 48 h. Thereafter, the animals were monitored for another 48 h and then dissected.

RESULTS

The APACHE II score significantly increased from baseline value in all groups during bacterial challenge. However, there were no between-group differences in APACHE II score. In contrast, pigs of the F-I and PS groups showed significant lower lung concentrations of P. aeruginosa (p<0.05 vs. control group) at autopsy.

CONCLUSION

These experimental data suggest that under comparable clinical conditions, a prophylactic immunization with anti-OprF-OprI immunoglobulin would not have an overall benefit to patients with P. aeruginosa sepsis.

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.

Characterization of two outer membrane protein antigens of Porphyromonas gingivalis that are protective in a murine lesion model

Porphyromonas gingivalis is a key periodontal pathogen that has been implicated in the aetiology of chronic adult periodontitis. The aim of this study was to characterize two potential vaccine candidates (PG32 and PG33) identified from a previous genomic sequence analysis. Gene knockout studies suggested that these proteins play an important role in bacterial growth and are transcriptionally linked. Analysis of 14 laboratory and clinical isolates of P. gingivalis found that in all strains, both genes were present with a high level of conservation and that the two proteins were also expressed in vitro. Truncated recombinant PG32 and PG33 proteins were produced in Escherichia coli in an attempt to increase the solubility of the proteins while retaining their native conformation. While most of the truncated proteins remained insoluble, two truncated proteins showed good solubility and high levels of protection in the P. gingivalis murine lesion model and may be considered as potential vaccine candidates for further testing in models of human periodontal disease.

Pseudomonas immunotherapy: a historical overview

The historic development of vaccines to be used as immunotherapy for Pseudomonas aeruginosa infections, in various patient populations, is reviewed. Commentary is offered concerning the relevance of each approach in light of our current understanding of the pathological process of these infections.

Clinical study to assess the immunogenicity and safety of a recombinant Pseudomonas aeruginosa OprF-OprI vaccine in burn patients

In a recent clinical trial we evaluated the safety and immunogenicity of a recombinant OprF-OprI vaccine consisting of the mature outer membrane protein I (OprI) and amino acids 190-342 of OprF of Pseudomonas aeruginosa in burn patients and compared the elicited antibodies with antibodies against tetanus as response to a simultaneous immunization given on the day of admission. Safety and immunogenicity of the vaccine had been tested before in healthy human volunteers as published in 1999. In this first clinical trial we immunized eight burn patients suffering from second or third degree burns involving between 35% and 55% of the body surface three times with 100 microg of the OprF-OprI vaccine. The vaccine was found to be very well tolerated. The patients did not show any serious side effects - and in particular no activation of the mediator cascade was observed. None of the subjects showed systemic P. aeruginosa infections during or after the treatment of their burns. The serological tests (ELISA) for detection of antibodies against P. aeruginosa and tetanus toxoid showed seroconversion for seven patients after inoculation. The data indicate that OprF-OprI can be a useful vaccine in the therapeutic management of burn injuries.

The C-terminal domain of Salmonella enterica serovar typhimurium OmpA is an immunodominant antigen in mice but appears to be only partially exposed on the bacterial cell surface

We examined the way the major outer membrane protein OmpA of Salmonella enterica serovar Typhimurium is recognized by the mouse immune system, by raising a panel of 12 monoclonal antibodies (MAbs) against this protein. Interaction between OmpA and these MAbs is competitively inhibited with several-hundredfold dilutions of mouse polyclonal sera obtained by immunization with live or heat-killed whole cells, suggesting that OmpA is one of the immunodominant antigens of serovar Typhimurium. All of the MAbs were specific for an identical epitope(s) located on the C-terminal domain of OmpA, as indicated by the use of OmpA fragments generated by protease or cyanogen bromide treatment and by competitive inhibition enzyme-linked immunosorbent assay. This epitope was highly conserved within (but not outside) the family Enterobacteriaceae: The strong immunogenicity of this epitope was surprising because the C-terminal domain of OmpA, usually thought to be located in the periplasm, is not expected to be exposed on the bacterial cell surface. A MAb, however, reacted in a cytofluorometry assay more strongly with outer-membrane-permeabilized cells than with untreated cells, a result supporting the predominantly periplasmic localization of the epitope. Significant, though low-level, reactivity of intact cells nevertheless suggests that in some cells the C-terminal domain of OmpA is exposed on the surface, a result consistent with the proposal that OmpA can fold into one of the two alternate conformations.

The C-terminal domain of Salmonella enterica serovar typhimurium OmpA is an immunodominant antigen in mice but appears to be only partially exposed on the bacterial cell surface

We examined the way the major outer membrane protein OmpA of Salmonella enterica serovar Typhimurium is recognized by the mouse immune system, by raising a panel of 12 monoclonal antibodies (MAbs) against this protein. Interaction between OmpA and these MAbs is competitively inhibited with several-hundredfold dilutions of mouse polyclonal sera obtained by immunization with live or heat-killed whole cells, suggesting that OmpA is one of the immunodominant antigens of serovar Typhimurium. All of the MAbs were specific for an identical epitope(s) located on the C-terminal domain of OmpA, as indicated by the use of OmpA fragments generated by protease or cyanogen bromide treatment and by competitive inhibition enzyme-linked immunosorbent assay. This epitope was highly conserved within (but not outside) the family Enterobacteriaceae: The strong immunogenicity of this epitope was surprising because the C-terminal domain of OmpA, usually thought to be located in the periplasm, is not expected to be exposed on the bacterial cell surface. A MAb, however, reacted in a cytofluorometry assay more strongly with outer-membrane-permeabilized cells than with untreated cells, a result supporting the predominantly periplasmic localization of the epitope. Significant, though low-level, reactivity of intact cells nevertheless suggests that in some cells the C-terminal domain of OmpA is exposed on the surface, a result consistent with the proposal that OmpA can fold into one of the two alternate conformations.

Safety and immunogenicity of an intranasal Pseudomonas aeruginosa hybrid outer membrane protein F-I vaccine in human volunteers

A hybrid protein [Met-Ala-(His)(6) OprF(190-342)-OprI(21-83)] consisting of the mature outer membrane protein I (OprI) and amino acids 190-342 of OprF of Pseudomonas aeruginosa was expressed in Escherichia coli and purified by Ni(2+) chelate-affinity chromatography. After several studies in healthy volunteers, as well as in patients, had proven the tolerability and immunogenicity of the the OprF-OprI vaccine, after intra-muscular application, we developed an emulgel for intranasal immunization. For this purpose we combined a highly concentrated OprF-I with sodium dodecylsulfate as vehicle and the gel matrix natriumlauryl sulfate. After safety and pyrogenicity evaluations in animals, eight healthy adult human volunteers received the OprF-I gel intranasally three times at 2-week intervals. The vaccination was well tolerated and no side effects were observed. An antibody induction (IgG and IgA) could be detected in the sera. These data support continued clinical investigation of the protection against infections in cystic fibrosis patients and patients prone to P. aeruginosa infections.

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

Three different variants of the recombinant hybrid outer membrane protein OprF (aa 190-342)-OprI (aa 21-83) could be obtained in high yield after expression in Escherichia coli. The hybrid protein was modified N terminally, either with a minimal histidine tag or with a homologous sequence of OprF. Both recombinant proteins were purified by nickel chelate affinity chromatography under native and denaturing conditions, and this produced three suitable candidates for a vaccination trial, protein His-F-I, which was purified in its native as well as in its refolded form; and the native purified N terminally extended protein, ex-F-I. In mice, significantly higher antibody titers and survival rates after challenge with Pseudomonas aeruginosa were observed following immunization with protein His-F-I, purified under native conditions.

Immunization with a chimeric tobacco mosaic virus containing an epitope of outer membrane protein F of Pseudomonas aeruginosa provides protection against challenge with P. aeruginosa

A chimeric tobacco mosaic virus (TMV) was constructed by inserting sequences representing peptide 9-14mer (TDAYNQKLSERRAN) of outer membrane (OM) protein F of Pseudomonas aeruginosa between amino acids Ser154 and Gly155 of the TMV coat protein (CP). This is the first example of TMV being used to construct a chimera containing a bacterial epitope. Mice immunized with TMV-9-14 produced anti-peptide-9-14mer-specific antibodies that reacted in whole-cell ELISA with all seven Fisher-Devlin (FD) immunotype strains of P. aeruginosa, reacted specifically by Western blotting with OM protein F extracted from all seven FD immunotypes, and were opsonic in opsonophagocytic assays. The chimeric TMV-9-14 vaccine afforded immunoprotection against challenge with wild-type P. aeruginosa in a mouse model of chronic pulmonary infection. TMV-9-14 is an excellent candidate for further development as a vaccine for possible use in humans to protect against P. aeruginosa infections.

Leptospiral outer membrane proteins OmpL1 and LipL41 exhibit synergistic immunoprotection

New vaccine strategies are needed for prevention of leptospirosis, a widespread human and veterinary disease caused by invasive spirochetes belonging to the genus Leptospira. We have examined the immunoprotective capacity of the leptospiral porin OmpL1 and the leptospiral outer membrane lipoprotein LipL41 in the Golden Syrian hamster model of leptospirosis. Specialized expression plasmids were developed to facilitate expression of leptospiral proteins in Escherichia coli as the membrane-associated proteins OmpL1-M and LipL41-M. Although OmpL1-M expression is highly toxic in E. coli, this was accomplished by using plasmid pMMB66-OmpL1, which has undetectable background expression without induction. LipL41-M expression and processing were enhanced by altering its lipoprotein signal peptidase cleavage site to mimic that of the murein lipoprotein. Active immunization of hamsters with E. coli membrane fractions containing a combination of OmpL1-M and LipL41-M was found to provide significant protection against homologous challenge with Leptospira kirschneri serovar grippotyphosa. At 28 days after intraperitoneal inoculation, survival in animals vaccinated with both proteins was 71% (95% confidence interval [CI], 53 to 89%), compared with only 25% (95% CI, 8 to 42%) in the control group (P < 0.001). On the basis of serological, histological, and microbiological assays, no evidence of infection was found in the vaccinated survivors. The protective effects of immunization with OmpL1-M and LipL41-M were synergistic, since significant levels of protection were not observed in animals immunized with either OmpL1-M or LipL41-M alone. In contrast to immunization with the membrane-associated forms of leptospiral proteins, hamsters immunized with His(6)-OmpL1 and His(6)-LipL41 fusion proteins, either alone or in combination, were not protected. These data indicate that the manner in which OmpL1 and LipL41 associates with membranes is an important determinant of immunoprotection.