Therapeutic administration of anti-PcrV F(ab')(2) in sepsis associated with Pseudomonas aeruginosa

Polyclonal anti-whole cell IgY passive immunotherapy shields against P. aeruginosa-induced acute pneumonia and burn wound infections in murine models

Pseudomonas aeruginosa (PA) is a multidrug-resistant (MDR) opportunistic pathogen causing severe hospital-, and community-acquired infections worldwide. Thus, the development of effective immunotherapy-based treatments is essential to combat the MDR-PA infections. In the current study, we evaluated the protective efficacy of polyclonal avian antibodies raised against inactivated whole cells of the PAO1 strain in murine models of acute pneumonia and burn wound. The efficacy of generated antibodies was evaluated against different PA strains through several in vitro, ex vivo and in vivo experiments. The results showed that the anti-PAO1-IgY effectively reduced the motility, biofilm formation and cell internalization ability, and enhanced the opsonophagocytic killing of PA strains through the formation of immobilized bacteria and induction of increased cell surface hydrophobicity. Furthermore, immunotherapy with anti-PAO1-IgY completely protected mice against all PA strains in both acute pneumonia and burn wound murine models. It was found to reduce the bacterial loads in infected burned mice through interfering with virulence factors that play vital roles in the early stages of PA infection, such as colonization and cell internalization. The immunotherapy with anti-PAO1-IgYs could be instrumental in developing effective therapies aimed at reducing the morbidity and mortality associated with PA infections.

Discovery of highly neutralizing human antibodies targeting Pseudomonas aeruginosa

Drug-resistant Pseudomonas aeruginosa (PA) poses an emerging threat to human health with urgent need for alternative therapeutic approaches. Here, we deciphered the B cell and antibody response to the virulence-associated type III secretion system (T3SS) in a cohort of patients chronically infected with PA. Single-cell analytics revealed a diverse B cell receptor repertoire directed against the T3SS needle-tip protein PcrV, enabling the production of monoclonal antibodies (mAbs) abrogating T3SS-mediated cytotoxicity. Mechanistic studies involving cryoelectron microscopy identified a surface-exposed C-terminal PcrV epitope as the target of highly neutralizing mAbs with broad activity against drug-resistant PA isolates. These anti-PcrV mAbs were as effective as treatment with conventional antibiotics in vivo. Our study reveals that chronically infected patients represent a source of neutralizing antibodies, which can be exploited as therapeutics against PA.

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.

Research Progress on Small Molecular Inhibitors of the Type 3 Secretion System

The overuse of antibiotics has led to severe bacterial drug resistance. Blocking pathogen virulence devices is a highly effective approach to combating bacterial resistance worldwide. Type three secretion systems (T3SSs) are significant virulence factors in Gram-negative pathogens. Inhibition of these systems can effectively weaken infection whilst having no significant effect on bacterial growth. Therefore, T3SS inhibitors may be a powerful weapon against resistance in Gram-negative bacteria, and there has been increasing interest in the research and development of T3SS inhibitors. This review outlines several reported small-molecule inhibitors of the T3SS, covering those of synthetic and natural origin, including their sources, structures, and mechanisms of action.

Immunogenicity and Protective Capacity of a Virus-like Particle Vaccine against Chlamydia trachomatis Type 3 Secretion System Tip Protein, CT584

An effective vaccine against Chlamydia trachomatis is urgently needed as infection rates continue to rise and C. trachomatis causes reproductive morbidity. An obligate intracellular pathogen, C. trachomatis employs a type 3 secretion system (T3SS) for host cell entry. The tip of the injectosome is composed of the protein CT584, which represents a potential target for neutralization with vaccine-induced antibody. Here, we investigate the immunogenicity and efficacy of a vaccine made of CT584 epitopes coupled to a bacteriophage virus-like particle (VLP), a novel platform for Chlamydia vaccines modeled on the success of HPV vaccines. Female mice were immunized intramuscularly, challenged transcervically with C. trachomatis, and assessed for systemic and local antibody responses and bacterial burden in the upper genital tract. Immunization resulted in a 3-log increase in epitope-specific IgG in serum and uterine homogenates and in the detection of epitope-specific IgG in uterine lavage at low levels. By contrast, sera from women infected with C. trachomatis and virgin controls had similarly low titers to CT584 epitopes, suggesting these epitopes are not systemically immunogenic during natural infection but can be rendered immunogenic by the VLP platform. C. trachomatis burden in the upper genital tract of mice varied after active immunization, yet passive protection was achieved when immune sera were pre-incubated with C. trachomatis prior to inoculation into the genital tract. These data demonstrate the potential for antibody against the T3SS to contribute to protection against C. trachomatis and the value of VLPs as a novel platform for C. trachomatis vaccines.

Pseudomonas aeruginosa Antivirulence Strategies: Targeting the Type III Secretion System

The Pseudomonas aeruginosa type III secretion system (T3SS) is a complex molecular machine that delivers toxic proteins from the bacterial cytoplasm directly into host cells. This apparatus spans the inner and outer membrane and employs a needle-like structure that penetrates through the eucaryotic cell membrane into the host cell cytosol. The expression of the P. aeruginosa T3SS is highly regulated by environmental signals including low calcium and host cell contact. P. aeruginosa strains with mutations in T3SS genes are less pathogenic, suggesting that the T3SS is a virulence mechanism. Given that P. aeruginosa is naturally antibiotic resistant and multidrug resistant isolates are rapidly emerging, new antibiotics to target P. aeruginosa are needed. Furthermore, even if new antibiotics were to be developed, the timeline between when an antibiotic is released and resistance development is relatively short. Therefore, the concept of targeting virulence factors has garnered attention. So-called "antivirulence" approaches do not kill the microbe but instead focus on rendering it harmless and therefore unable to cause damage. Since these therapies target a particular system or pathway, the normal microbiome is unlikely to be affected and there is less concern about the spread to other microbes. Finally, and most importantly, since any antivirulence drug does not kill the microbe, there should be less selective pressure to develop resistance to these inhibitors. The P. aeruginosa T3SS has been well studied due to its importance for pathogenesis in numerous human and animal infections. Thus, many P. aeruginosa T3SS inhibitors have been described as potential antivirulence therapeutics, some of which have progressed to clinical trials.

Potential Therapeutic Targets for Combination Antibody Therapy against Pseudomonas aeruginosa Infections

Despite advances in antimicrobial therapy and even the advent of some effective vaccines, Pseudomonas aeruginosa (P. aeruginosa) remains a significant cause of infectious disease, primarily due to antibiotic resistance. Although P. aeruginosa is commonly treatable with readily available therapeutics, these therapies are not always efficacious, particularly for certain classes of patients (e.g., cystic fibrosis (CF)) and for drug-resistant strains. Multi-drug resistant P. aeruginosa infections are listed on both the CDC’s and WHO’s list of serious worldwide threats. This increasing emergence of drug resistance and prevalence of P. aeruginosa highlights the need to identify new therapeutic strategies. Combinations of monoclonal antibodies against different targets and epitopes have demonstrated synergistic efficacy with each other as well as in combination with antimicrobial agents typically used to treat these infections. Such a strategy has reduced the ability of infectious agents to develop resistance. This manuscript details the development of potential therapeutic targets for polyclonal antibody therapies to combat the emergence of multidrug-resistant P. aeruginosa infections. In particular, potential drug targets for combinational immunotherapy against P. aeruginosa are identified to combat current and future drug resistance.

Passive immunization with anti- chimeric protein PilQ/PilA -DSL region IgY does not protect against mortality associated with Pseudomonas aeruginosa sepsis in a rabbit model

BACKGROUND

Pseudomonas aeruginosa sepsis is associated with unacceptably high mortality and, for many of those who survive, long-term morbidity. The aims of this study were to production of IgY against chimeric protein pilQ-pilA-DSL region and killed- whole cell Pseudomonas aeruginosa O1 (PAO1) strain and their efficacy for immunoprophylaxis of sepsis caused by P. aeruginosa in a rabbit model.

METHODS

Specific IgY was obtained by immunization of hens. The purity of IgY was determined by SDS-PAGE analysis. The effect of IgY on growth and hydrophobicity of P. aeruginosa were performed through time-kill assay and microbial adhesion to hydrocarbons test (MATH), respectively. The efficacy of specific IgYs was examined against P. aeruginosa sepsis in a rabbit model. The rabbits were monitored for 72 h to record physiological characters and survival. Hematologic factors, C-reactive protein, pro-inflammatory cytokines, and bacterial count from blood and solid organs were measured, periodically.

RESULTS

We found that the growth inhibitory effect of the anti- killed whole cell IgY was higher than anti-pilQ-pilA IgY (P < 0.001). The hydrophobicity effect of PAO1 increased when bacteria were opsonized by anti- killed whole cell IgY while the hydrophobicity activity was decreased following incubation of PAO1 with anti-pilQ-pilA IgY in a broth medium (P < 0.001). Following intravenous (IV) administration of produced IgYs, no significant difference was observed in the survival, decrease in inflammatory mediators and clinical symptoms between the groups 48h post infection (P > 0.05). Moreover, no considerable decrease was observed in the bacterial load of blood, lungs and kidneys in rabbits treated with specific IgYs and control groups (P > 0.05). No bacteria were found in the spleen and liver samples from infected rabbits.

CONCLUSION

Although produced IgYs had a good immunoreactivity, IV immunization of IgYs was not protective against P. aeruginosa sepsis in the rabbit model. Further studies are needed to assess the immune response and decreasing mortality rate using the rabbit sepsis model.

Type 3 secretion system as an anti-Pseudomonal target

Type 3 secretion systems (T3SSs) are a series of mechanisms involved in bacterial pathogenesis. While Pseudomonas aeruginosa only possess one T3SS, it plays a key role in the virulence of P. aeruginosa virulence. This finding suggests that T3SS impairment may be an alternative for antimicrobial agents, allowing P. aeruginosa infections to be directly combated avoiding antimicrobial pressure on this and other microorganisms. To date, different approaches have been proposed, including T3SS inhibition, vaccination strategies, development of anti-T3SS antibodies and gene silencing.

Identification of Small Molecules Blocking the Pseudomonas aeruginosa type III Secretion System Protein PcrV

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that employs its type III secretion system (T3SS) during the acute phase of infection to translocate cytotoxins into the host cell cytoplasm to evade the immune system. The PcrV protein is located at the tip of the T3SS, facilitates the integration of pore-forming proteins into the eukaryotic cell membrane, and is required for translocation of cytotoxins into the host cell. In this study, we used surface plasmon resonance screening to identify small molecule binders of PcrV. A follow-up structure-activity relationship analysis resulted in PcrV binders that protect macrophages in a P. aeruginosa cell-based infection assay. Treatment of P. aeruginosa infections is challenging due to acquired, intrinsic, and adaptive resistance in addition to a broad arsenal of virulence systems such as the T3SS. Virulence blocking molecules targeting PcrV constitute valuable starting points for development of next generation antibacterials to treat infections caused by P. aeruginosa.

Multifunctional Monoclonal Antibody Targeting Pseudomonas aeruginosa Keratitis in Mice

A worrisome trend in the study and treatment of infectious disease noted in recent years is the increase in multidrug resistant strains of bacteria concurrent with a scarcity of new antimicrobial agents to counteract this rise. This is particularly true amongst bacteria within the Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species (ESKAPE) designation. P. aeruginosa is one of the most common causes of bacterial keratitis. Therefore, it is of vital importance to characterize new antimicrobial agents with anti-Pseudomonal activity for use with the ocular surface. MEDI3902 is a multifunctional antibody that targets the P. aeruginosa persistence factor Psl exopolysaccharide, and the type 3 secretion protein PcrV. We initially assessed this antibody for ocular surface toxicity. The antimicrobial activity of the antibody was then tested by treating mice with established P. aeruginosa keratitis with both topical and intravenous treatment modalities. MEDI3902, was shown to be non-toxic to the ocular surface of mice when given topically. It was also effective compared to the control antibody at preventing P. aeruginosa keratitis with a one-time treatment at the time of infection. Both topical and intravenous administration of MEDI3902 has been proved significant in treating established keratitis infections as well, speeding the resolution of infection significantly more than that of the control IgG. We report the first use of a topical immunotherapeutic multifunctional agent targeting Psl and type 3 secretion on the ocular surface as an antimicrobial agent. While MEDI3902 has been shown to prevent Pseudomonas biofilm formation in keratitis models when given prophylactically intravitally, we show that MEDI3902 has the capability to also treat an active infection when given intravenously to mice with Pseudomonas keratitis. Our data indicate antibodies are well tolerated and nontoxic on the ocular surface. They reduce infection in mice treated concurrently at inoculation and reduced the signs of cornea pathology in mice with established infection. Taken together, these data indicate treatment with monoclonal antibodies directed against Psl and PcrV may be clinically effective in the treatment of P. aeruginosa keratitis and suggest that the design of further antibodies to be an additional tool in the treatment of bacterial keratitis.

Antibodies Inhibiting the Type III Secretion System of Gram-Negative Pathogenic Bacteria

Pathogenic bacteria are a global health threat, with over 2 million infections caused by Gram-negative bacteria every year in the United States. This problem is exacerbated by the increase in resistance to common antibiotics that are routinely used to treat these infections, creating an urgent need for innovative ways to treat and prevent virulence caused by these pathogens. Many Gram-negative pathogenic bacteria use a type III secretion system (T3SS) to inject toxins and other effector proteins directly into host cells. The T3SS has become a popular anti-virulence target because it is required for pathogenesis and knockouts have attenuated virulence. It is also not required for survival, which should result in less selective pressure for resistance formation against T3SS inhibitors. In this review, we will highlight selected examples of direct antibody immunizations and the use of antibodies in immunotherapy treatments that target the bacterial T3SS. These examples include antibodies targeting the T3SS of Pseudomonas aeruginosa, Yersinia pestis, Escherichia coli, Salmonella enterica, Shigella spp., and Chlamydia trachomatis.

Epidemiological survey of serum titers from adults against various Gram-negative bacterial V-antigens

The V-antigen, a virulence-associated protein, was first identified in Yersinia pestis more than half a century ago. Since then, other V-antigen homologs and orthologs have been discovered and are now considered as critical molecules for the toxic effects mediated by the type III secretion system during infections caused by various pathogenic Gram-negative bacteria. After purifying recombinant V-antigen proteins, including PcrV from Pseudomonas aeruginosa, LcrV from Yersinia, LssV from Photorhabdus luminescens, AcrV from Aeromonas salmonicida, and VcrV from Vibrio parahaemolyticus, we developed an enzyme-linked immunoabsorbent assay to measure titers against each V-antigen in sera collected from 186 adult volunteers. Different titer-specific correlation levels were determined for the five V-antigens. The anti-LcrV and anti-AcrV titers shared the highest correlation with each other with a correlation coefficient of 0.84. The next highest correlation coefficient was between anti-AcrV and anti-VcrV titers at 0.79, while the lowest correlation was found between anti-LcrV and anti-VcrV titers, which were still higher than 0.7. Sera from mice immunized with one of the five recombinant V-antigens displayed cross-antigenicity with some of the other four V-antigens, supporting the results from the human sera. Thus, the serum anti-V-antigen titer measurement system may be used for epidemiological investigations of various pathogenic Gram-negative bacteria.

Immunoglobulin for Treating Bacterial Infections: One More Mechanism of Action

The mechanisms underlying the effects of immunoglobulins on bacterial infections are thought to involve bacterial cell lysis via complement activation, phagocytosis via bacterial opsonization, toxin neutralization, and antibody-dependent cell-mediated cytotoxicity. Nevertheless, recent advances in the study of the pathogenicity of Gram-negative bacteria have raised the possibility of an association between immunoglobulin and bacterial toxin secretion. Over time, new toxin secretion systems like the type III secretion system have been discovered in many pathogenic Gram-negative bacteria. With this system, the bacterial toxins are directly injected into the cytoplasm of the target cell through a special secretory apparatus without any exposure to the extracellular environment, and therefore with no opportunity for antibodies to neutralize the toxin. However, antibodies against the V-antigen, which is located on the needle-shaped tip of the bacterial secretion apparatus, can inhibit toxin translocation, thus raising the hope that the toxin may be susceptible to antibody targeting. Because multi-drug resistant bacteria are now prevalent, inhibiting this secretion mechanism is an attractive alternative or adjunctive therapy against lethal bacterial infections. Thus, it is not unreasonable to define the blocking effect of anti-V-antigen antibodies as the fifth mechanism for immunoglobulin action against bacterial infections.

Anti-PcrV IgY antibodies protect against Pseudomonas aeruginosa infection in both acute pneumonia and burn wound models

Pseudomonas aeruginosa is a common nosocomial pathogen in burn patients, and rapidly acquires antibiotic resistance; thus, developing an effective therapeutic approach is the most promising strategy for combating infection. Type III secretion system (T3SS) translocates bacterial toxins into the cytosol of the targeted eukaryotic cells, which plays important roles in the virulence of P. aeruginosa infections in both acute pneumonia and burn wound models. The PcrV protein, a T3SS translocating protein, is required for T3SS function and is a well-validated target in animal models of immunoprophylactic strategies targeting P. aeruginosa. In the present study, we evaluated the protective efficacy of chicken egg yolk antibodies (IgY) raised against recombinant PcrV (r-PcrV) in both acute pneumonia and burn wound models. R-PcrV protein was generated by expressing the pcrV gene (cloned in pET-28a vector) in E. coli BL-21. Anti-PcrV IgY was obtained by immunization of hen. Anti-PcrV IgY induced greater protection in P. aeruginosamurine acute pneumonia and burn wound models than control IgY (C-IgY) and PBS groups. Anti-PcrV IgY improved opsonophagocytic killing and inhibition of bacterial invasion of host cells. Taken together, our data provide evidence that anti-PcrV IgY can be a promising therapeutic candidate for combating P. aeruginosa infections.

Anti-PcrV titers in non-cystic fibrosis patients with Pseudomonas aeruginosa respiratory tract infection

OBJECTIVE

The epidemiology and role of the anti-PcrV titer in non-cystic fibrosis patients with Pseudomonas aeruginosa airway tract infections is not fully understood. This study was performed to compare the anti-PcrV titers of patients with and without P. aeruginosa respiratory tract infections.

METHODS

This prospective cohort study was conducted at Hokkaido University Hospital in Japan. Participants had blood and sputum specimens collected on admission. They were divided into two groups based on their sputum culture results. Those with a P. aeruginosa infection were assigned to the P. aeruginosa (PA) group and those without a P. aeruginosa infection were assigned to the non-PA group. Serum anti-PcrV titers were measured using a validated ELISA.

RESULTS

Of the 44 participants, 15 were assigned to the PA group and 29 were assigned to the non-PA group. In the PA group, 10/15 participants (66.7%) had an anti-PcrV titer >1000ng/ml compared to 3/29 participants (10.3%) in the non-PA group (p<0.001). In the PA group, two of the five participants with an anti-PcrV titer <1000 ng/ml died of recurrent P. aeruginosa pneumonia; the other three participants did not develop pneumonia.

CONCLUSION

The anti-PcrV titers in participants with P. aeruginosa infection varied considerably. Patients with low anti-PcrV titers and refractory P. aeruginosa infections need to be monitored closely.

Rational Design of a Chimeric Derivative of PcrV as a Subunit Vaccine Against Pseudomonas aeruginosa

Pseudomonas aeruginosa (PA) is a major cause of nosocomial infections, which remain an unsolved problem in the clinic despite conventional antibiotic treatment. A PA vaccine could be both an effective and economical strategy to address this issue. Many studies have shown that PcrV, a structural protein of the type 3 secretion system (T3SS) from PA, is an ideal target for immune prevention and therapy. However, difficulties in the production of high-quality PcrV likely hinder its further application in the vaccine industry. Thus, we hypothesized that an optimized PcrV derivative with a rational design could be produced. In this study, the full-length PcrV was divided into four domains with the guidance of its structure, and the Nter domain (Met1-Lys127) and H12 domain (Leu251-Ile294) were found to be immunodominant. Subsequently, Nter and H12 were combined with a flexible linker to generate an artificial PcrV derivative (PcrVNH). PcrVNH was successfully produced in E. coli and behaved as a homogenous monomer. Moreover, immunization with PcrVNH elicited a multifactorial immune response and conferred broad protection in an acute PA pneumonia model and was equally effective to full-length PcrV. In addition, passive immunization with anti-PcrVNH antibodies alone also showed significant protection, at least based on inhibition of the T3SS and mediation of opsonophagocytic killing activities. These results provide an additional example for the rational design of antigens and suggest that PcrVNH is a promising vaccine candidate for the control of PA infection.

Drug Prevention and Control of Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) is one of the most prevalent and serious complications of mechanical ventilation, which is considered a common nosocomial infection in critically ill patients. There are some great options for the prevention of VAP: (i) minimize ventilator exposure; (ii) intensive oral care; (iii) aspiration of subglottic secretions; (iv) maintain optimal positioning and encourage mobility; and (v) prophylactic probiotics. Furthermore, clinical management of VAP depends on appropriate antimicrobial therapy, which needs to be selected based on individual patient factors, such as previous antibacterial therapy, history of hospitalization or mechanical ventilation, and bacterial pathogens and antibiotic resistance patterns. In fact, antibiotic resistance has exponentially increased over the last decade, and the isolation of a multidrug-resistant (MDR) pathogen has been identified as an independent predictor of inadequate initial antibiotic therapy and which is significantly associated with increased mortality. Multiple attempts were used in the treatment of VAP, such as novel antibacterial agents, inhaled antibiotics and monoclonal antibodies. In this review, we summarize the current therapeutic options for the prevention and treatment of VAP, aiming to better management of VAP in clinical practice.

The protective effects of nasal PcrV-CpG oligonucleotide vaccination against Pseudomonas aeruginosa pneumonia

An effective vaccine against Pseudomonas aeruginosa would be hugely beneficial to people who are susceptible to the serious infections it can cause. Vaccination against PcrV of the P. aeruginosa type III secretion system is a potential prophylactic strategy for improving the incidence and prognosis of P. aeruginosa pneumonia. Here, the effect of nasal PcrV adjuvanted with CpG oligodeoxynucleotide (CpG) was compared with a nasal PcrV/aluminum hydroxide gel (alum) vaccine. Seven groups of mice were vaccinated intranasally with one of the following: 1, PcrV-CpG; 2, PcrV-alum; 3, PcrV alone; 4, CpG alone; 5, alum alone; 6 and 7, saline control. Fifty days after the first immunization, anti-PcrV IgG, IgA and IgG isotype titers were measured; significant increases in these titers were detected only in the PcrV-CpG vaccinated mice. The vaccinated mice were then intratracheally infected with a lethal dose of P. aeruginosa and their body temperatures and survival monitored for 24 hr, edema, bacteria, myeloperoxidase activity and lung histology also being evaluated at 24 hr post-infection. It was found that 73% of the PcrV-CpG-vaccinated mice survived, whereas fewer than 30% of the mice vaccinated with PcrV-alum or adjuvant alone survived. Lung edema and other inflammation-related variables were less severe in the PcrV-CpG group. The significant increase in PcrV-specific IgA titers detected following PcrV-CpG vaccination is probably a component of the disease protection mechanism. Overall, our data show that intranasal PcrV-CpG vaccination has potential efficacy for clinical application against P. aeruginosa pneumonia.

Construction of a Protective Vaccine Against Lipopolysaccharide-Heterologous Pseudomonas aeruginosa Strains Based on Expression Profiling of Outer Membrane Proteins During Infection

Pseudomonas aeruginosa is a ubiquitous opportunistic pathogen, which causes infectious disease in patients with cystic fibrosis and compromised immunity. P. aeruginosa is difficult to eradicate because of its intrinsic resistance to most traditional antibiotics as well as acquired resistance mechanisms after decades of antibiotic usage. A full understanding of the P. aeruginosa pathogenesis mechanisms is necessary for the development of novel prevention and treatment strategies. To identify novel vaccine candidates, here we comprehensively examined the expression levels of all the known outer membrane proteins in two P. aeruginosa strains in a murine acute pneumonia model. OprH was one of the most highly expressed proteins during infection. In addition, OprH is known to be highly immunogenic and accessible by host proteins. Thus, it was chosen as a vaccine candidate. To further identify vaccine candidates, 34 genes highly expressed during infection were evaluated for their contributions in virulence by testing individual transposon insertion mutants. Among them, fpvA, hasR, and foxA were found essential for bacterial virulence and therefore included in vaccine construction. Immunization with a mixture of FpvA, HasR, and FoxA rendered no protection, however, while immunization by OprH refolded in liposomes elicited specific opsonic antibodies and conferred protection against two lipopolysaccharide-heterologous P. aeruginosa strains (PA14 and PA103). Overall, by studying the expression profile of the P. aeruginosa outer membrane proteins during infection, we identified OprH as a potential vaccine candidate for the prevention of lung infection by P. aeruginosa.

Therapeutic antibodies: A new era in the treatment of respiratory diseases?

Respiratory diseases affect millions of people worldwide, and account for significant levels of disability and mortality. The treatment of lung cancer and asthma with therapeutic antibodies (Abs) is a breakthrough that opens up new paradigms for the management of respiratory diseases. Antibodies are becoming increasingly important in respiratory medicine; dozens of Abs have received marketing approval, and many more are currently in clinical development. Most of these Abs target asthma, lung cancer and respiratory infections, while very few target chronic obstructive pulmonary disease - one of the most common non-communicable causes of death - and idiopathic pulmonary fibrosis. Here, we review Abs approved for or in clinical development for the treatment of respiratory diseases. We notably highlight their molecular mechanisms, strengths, and likely future trends.

KB001-A, a novel anti-inflammatory, found to be safe and well-tolerated in cystic fibrosis patients infected with Pseudomonas aeruginosa

BACKGROUND

Chronic Pseudomonas aeruginosa (Pa) airways infection, exuberant local inflammation, and progressive lung function loss are hallmarks of cystic fibrosis (CF). KB001-A is an anti-PcrV PEGylated monoclonal antibody fragment to the Type III secretion system of Pa. This 16-week study evaluated KB001-A associated effect on time-to-need for antibiotics for worsening respiratory signs and symptoms, as well as safety, and treatment-associated changes in symptom scores, inflammatory markers, and spirometry.

METHODS

This was a randomized, double-blind, placebo-controlled, repeat-dose study in CF subjects with Pa. Intravenous 10mg/kg KB001-A or placebo infusions were administered at baseline and weeks 2, 4, 8, and 16, with a 4-week follow-up. Sputum inflammatory markers were assessed in a sub-study. Time-to-need for antibiotics was compared between groups by Kaplan Meier analysis and Cox proportional hazards modeling adjusting for randomization strata.

RESULTS

Of 182 subjects, 169 received at least one infusion of KB001-A (n=83) or placebo (n=86). KB001-A was generally safe and well-tolerated as compared to placebo, with no significant emergent adverse effects other than one serious adverse event of elevated hepatic enzymes of unclear etiology. Time to need for antibiotics did not differ between groups (HR: 1.00; 95% CI: 0.69, 1.45, p=0.995). A 3.2 increase in ppFEV₁ from placebo favoring KB001-A was observed at week 16 (95% CI: 1.12, 5.30, p=0.003). Mean changes from baseline in log₁₀ sputum neutrophil elastase (NE) had a non-significant decrease (-0.27, 95% CI: -0.58,0.04, p=0.084) while IL-8 concentrations at week 16 were significantly lower (-0.27, 95% CI: -0.55,0.00, p=0.048) among KB001-A subjects (n=16) relative to placebo (n=13).

CONCLUSIONS

KB001-A was safe and well-tolerated and associated with a modest FEV₁ benefit and reduction in select sputum inflammatory markers (IL-8). KB001-A was not associated with an increased time to need for antibiotics. The lack of efficacy seen with KB001-A may be due, in part, to the low levels of the type III secretion proteins previously reported in sputum of CF patients chronically infected with Pa.

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.

Epidemiological analysis of serum anti-Pseudomonas aeruginosa PcrV titers in adults

Of the various virulence mechanisms of the opportunistic pathogen Pseudomonas aeruginosa, the type III secretion system (TTSS) has been characterized as a major factor associated with acute lung injury, bacteremia and mortality. In addition, PcrV, a component protein of the TTSS, has been characterized as a protective antigen against infection with P. aeruginosa. This study comprised an epidemiological analysis of serum anti-PcrV titers in a cohort of Japanese adults. From April 2012 to March 2013, serum anti-PcrV titers of 198 volunteer participants undergoing anesthesia for scheduled surgeries were measured. The median, minimum and maximum serum anti-PcrV titers among the 198 participants were 4.09 nM, 1.01 nM and 113.81 nM, respectively. The maximum peaks in the histogram were within the anti-PcrV 2.00-4.99 nM titer range; values for 115 participants (58.1%) were within this range. Anti-PcrV titers were more than approximately three-fold greater (>12 nM) than the median value in 21 participants (10.6%). Ten-year interval age increases, history of treatment for traffic trauma, and a history of past surgery each showed statistically significant associations with higher anti-PcrV titers (i.e., >10 nM) than did the other factors assessed by binomial analysis. This study revealed a considerable variation in anti-PcrV titers in adult subjects without any obvious histories of infection with P. aeruginosa.

The prophylactic effects of human IgG derived from sera containing high anti-PcrV titers against pneumonia-causing Pseudomonas aeruginosa

The PcrV cap structure of the type III secretory apparatus of Pseudomonas aeruginosa is a vaccine target. Human immunoglobulin G (IgG) molecules extracted from sera containing high or low anti-PcrV titers were tested for their effects against P. aeruginosa pneumonia in a mouse model. Among 198 volunteers, we selected the top 10 high anti-PcrV titer sera and the bottom 10 low anti-PcrV titer sera and extracted the IgG fraction from each serum sample. First, we examined the effects of the IgG against virulent P. aeruginosa. A lethal dose of P. aeruginosa premixed with saline, low titer human IgG, high titer human IgG, or rabbit-derived polyclonal anti-PcrV IgG was intratracheally administered into the lungs of mice, and their survival and lung inflammation were evaluated for 24 h. The high anti-PcrV titer human IgG had a prophylactic effect. Next, the prophylactic effects of intravenous administration of extracted and pooled high or low anti-PcrV titer human IgG were examined. Here, prophylactic intravenous administration of pooled high anti-PcrV titer human IgG, which showed binding capacity to P. aeruginosa PcrV, was more effective than the administration of its low titer pooled equivalent, and the measured physiological and inflammatory parameters correlated with the anti-PcrV titer levels. This result indirectly implies that high anti-PcrV titers in blood can help to protect against virulent P. aeruginosa infections. In addition, the IgG fractions from such high titer sera have potential to be a source of specific intravenous immunoglobulin products for passive vaccination against virulent P. aeruginosa infections.

High Throughput Combinatorial Formatting of PcrV Nanobodies for Efficient Potency Improvement

Improving potencies through concomitant blockage of multiple epitopes and avid binding by fusing multiple (different) monovalent Nanobody building blocks via linker sequences into one multivalent polypeptide chain is an elegant alternative to affinity maturation. We explored a large and random formatting library of bivalent (combinations of two identical) and biparatopic (combinations of two different) Nanobodies for functional blockade of Pseudomonas aeruginosa PcrV. PcrV is an essential part of the P. aeruginosa type III secretion system (T3SS), and its oligomeric nature allows for multiple complex binding and blocking options. The library screening yielded a large number of promising biparatopic lead candidates, revealing significant (and non-trivial) preferences in terms of Nanobody building block and epitope bin combinations and orientations. Excellent potencies were confirmed upon further characterization in two different P. aeruginosa T3SS-mediated cytotoxicity assays. Three biparatopic Nanobodies were evaluated in a lethal mouse P. aeruginosa challenge pneumonia model, conferring 100% survival upon prophylactic administration and reducing lung P. aeruginosa burden by up to 2 logs. At very low doses, they protected the mice from P. aeruginosa infection-related changes in lung histology, myeloperoxidase production, and lung weight. Importantly, the most potent Nanobody still conferred protection after therapeutic administration up to 24 h post-infection. The concept of screening such formatting libraries for potency improvement is applicable to other targets and biological therapeutic platforms.

IV Immunoglobulin for Acute Lung Injury and Bacteremia in Pseudomonas aeruginosa Pneumonia

OBJECTIVES

Virulent and multidrug-resistant Pseudomonas aeruginosa causes a lethal pneumonia, especially in patients who are artificially ventilated. It has been reported that the virulence mechanism used by P. aeruginosa, which is linked to acute lung injury, is strongly associated with the type III secretion system, and specific antibodies targeting this system have shown a protective effect in both experimental and clinical settings. We investigated the effect of administering IV immunoglobulins on P. aeruginosa pneumonia, including its associated bacteremia and mortality, although focusing especially on type III secretion system-associated P. aeruginosa virulence.

DESIGN

Prospective randomized and controlled animal study.

SETTING

University laboratory.

SUBJECTS

Male ICR mice.

INTERVENTIONS

Mice were infected intratracheally with a lethal dose of the virulent P. aeruginosa PA103 strain. IV immunoglobulin administration was examined in three different settings: 1) premixed; 2) pre-IV, prophylactic administration before bacterial infection; and 3) post-IV, therapeutic administration after bacterial infection. The effect of specific antigen titer depletion of IV immunoglobulins was also examined.

MEASUREMENTS AND MAIN RESULTS

Survival and body temperature were monitored for 24 hours. Bacteremia, cytokine concentration, myeloperoxidase activity, WBC counts in the blood, and lung bacterial load were evaluated. Survival improved significantly in mice that received IV immunoglobulins (p < 0.05). Lung edema, lung bacteriologic load, and bacteremia decreased significantly in the IV immunoglobulin-treated mice (p < 0.05). The mechanism of protection was associated with the presence of antibodies against both PcrV and some bacterial surface antigens in the IV immunoglobulins.

CONCLUSIONS

IV immunoglobulin administration had a significantly protective effect against lethal infection from virulent P. aeruginosa. Prophylactic IV immunoglobulin administration at the highest dose was comparable with that achieved by administrating a specific anti-PcrV polyclonal IgG into the mice. The mechanism of protection is likely to involve the synergic action of anti-PcrV titers and antibodies against some surface antigen(s) that block the type III secretion system-associated virulence of P. aeruginosa.

Investigational drugs in phase I and phase II clincial trials for the treatment of hospital-acquired pneumonia

INTRODUCTION

Hospital acquired pneumonia (HAP) is one of the main infections acquired by patients during a stay in hospital. The main issue when dealing with patients with HAP and ventilator associated pneumonia (VAP) is the increasing role of multi-drug resistant organisms (MDROs).

AREAS COVERED

In this review the authors summarize the actual situation of MDROs as a cause of HAP and VAP. They also review the current treatment options stated in the most important international guidelines. Finally, they focus on the investigational drugs that have reached the phase III stage of development and the novel compounds that are being studied in phase I and II clinical trials.

EXPERT OPINION

Thanks to their excellent activity against MDROs, drugs in development for the treatment of HAP and VAP can significantly improve the therapeutic options available. In selected patients, the possibility to administer directed therapy with monoclonal antibodies to specific pathogens is an exciting strategy in the fight against widespread resistance.

Innate Immune Signaling Activated by MDR Bacteria in the Airway

Health care-associated bacterial pneumonias due to multiple-drug resistant (MDR) pathogens are an important public health problem and are major causes of morbidity and mortality worldwide. In addition to antimicrobial resistance, these organisms have adapted to the milieu of the human airway and have acquired resistance to the innate immune clearance mechanisms that normally prevent pneumonia. Given the limited efficacy of antibiotics, bacterial clearance from the airway requires an effective immune response. Understanding how specific airway pathogens initiate and regulate innate immune signaling, and whether this response is excessive, leading to host-induced pathology may guide future immunomodulatory therapy. We will focus on three of the most important causes of health care-associated pneumonia, Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae, and review the mechanisms through which an inappropriate or damaging innate immune response is stimulated, as well as describe how airway pathogens cause persistent infection by evading immune activation.

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.

Anti-PcrV antibody strategies against virulent Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that causes fatal acute lung infections in critically ill individuals. Its pathogenesis is associated with bacterial virulence conferred by the type III secretion system (TTSS), through which P. aeruginosa causes necrosis of the lung epithelium and disseminates into the circulation, resulting in bacteremia, sepsis, and mortality. TTSS allows P. aeruginosa to directly translocate cytotoxins into eukaryotic cells, inducing cell death. The P. aeruginosa V-antigen PcrV, a homolog of the Yersinia V-antigen LcrV, is an indispensable contributor to TTS toxin translocation. Vaccination against PcrV ensures the survival of challenged mice and decreases lung inflammation and injury. Both the rabbit polyclonal anti-PcrV antibody and the murine monoclonal anti-PcrV antibody, mAb166, inhibit TTS toxin translocation. mAb166 IgG was cloned, and a molecular engineered humanized anti-PcrV IgG antigen-binding fragment, KB001, was developed for clinical use. KB001 is currently undergoing Phase-II clinical trials for ventilator-associated pneumonia in France and chronic pneumonia in cystic fibrosis in USA. In these studies, KB001 has demonstrated its safety, a favorable pharmacokinetic profile, and promising potential as a nonantibiotic strategy to reduce airway inflammation and damage in P. aeruginosa pneumonia.

Association between Pseudomonas aeruginosa type III secretion, antibiotic resistance, and clinical outcome: a review

Pseudomonas aeruginosa uses a complex type III secretion system to inject the toxins ExoS, ExoT, ExoU, and ExoY into the cytosol of target eukaryotic cells. This system is regulated by the exoenzyme S regulon and includes the transcriptional activator ExsA. Of the four toxins, ExoU is characterized as the major virulence factor responsible for alveolar epithelial injury in patients with P. aeruginosa pneumonia. Virulent strains of P. aeruginosa possess the exoU gene, whereas non-virulent strains lack this particular gene. The mechanism of virulence for the exoU⁺ genotype relies on the presence of a pathogenic gene cluster (PAPI-2) encoding exoU and its chaperone, spcU. The ExoU toxin has a patatin-like phospholipase domain in its N-terminal, exhibits phospholipase A₂ activity, and requires a eukaryotic cell factor for activation. The C-terminal of ExoU has a ubiquitinylation mechanism of activation. This probably induces a structural change in enzymatic active sites required for phospholipase A₂ activity. In P. aeruginosa clinical isolates, the exoU⁺ genotype correlates with a fluoroquinolone resistance phenotype. Additionally, poor clinical outcomes have been observed in patients with pneumonia caused by exoU⁺-fluoroquinolone-resistant isolates. Therefore, the potential exists to improve clinical outcomes in patients with P. aeruginosa pneumonia by identifying virulent and antimicrobial drug-resistant strains through exoU genotyping or ExoU protein phenotyping or both.

Anti-PcrV antibody in cystic fibrosis: a novel approach targeting Pseudomonas aeruginosa airway infection

Pseudomonas aeruginosa (Pa) airway infection is associated with increased morbidity and mortality in cystic fibrosis (CF). The type III secretion system is one of the factors responsible for the increased virulence and pro-inflammatory effects of Pa. KB001 is a PEGylated, recombinant, anti-Pseudomonas-PcrV antibody Fab' fragment that blocks the function of Pa TTSS. We studied the safety, pharmacokinetic (PK), and pharmacodynamic properties of KB001 in CF subjects with chronic Pa infection. Twenty-seven eligible CF subjects (≥12 years of age, FEV1 ≥40% of predicted, and sputum Pa density >10(5)  CFU/g) received a single intravenous dose of KB001 (3 mg/kg or 10 mg/kg) or placebo. Safety, PK, Pa density, clinical outcomes, and inflammatory markers were assessed. KB001 had an acceptable safety profile and a mean serum half-life of 11.9 days. All subjects had Pa TTSS expression in sputum. There were no significant differences between KB001 and placebo for changes in Pa density, symptoms, or spirometry after a single dose. However, compared to baseline, at Day 28 there was a trend towards a dose-dependent reduction in sputum myeloperoxidase, IL-1, and IL-8, and there were significant overall differences in change in sputum neutrophil elastase and neutrophil counts favoring the KB001 10 mg/kg group versus placebo (-0.61 log(10) and -0.63 log(10) , respectively; P < 0.05). These results support targeting Pa TTSS with KB001 as a nonantibiotic strategy to reduce airway inflammation and damage in CF patients with chronic Pa infection. Repeat-dosing studies are necessary to evaluate the durability of the anti-inflammatory effects and how that may translate into clinical benefit. (NCT00638365).

A novel anti-PcrV antibody providing enhanced protection against Pseudomonas aeruginosa in multiple animal infection models

Pseudomonas aeruginosa is a major cause of hospital-acquired infections, particularly in mechanically ventilated patients, and it is the leading cause of death in cystic fibrosis patients. A key virulence factor associated with disease severity is the P. aeruginosa type III secretion system (T3SS), which injects bacterial toxins directly into the cytoplasm of host cells. The PcrV protein, located at the tip of the T3SS injectisome complex, is required for T3SS function and is a well-validated target in animal models of immunoprophylactic strategies targeting P. aeruginosa. In an effort to identify a highly potent and protective monoclonal antibody (MAb) that inhibits the T3SS, we generated and characterized a panel of novel anti-PcrV MAbs. Interestingly, some MAbs exhibiting potent inhibition of T3SS in vitro failed to provide protection in a mouse model of P. aeruginosa infection, suggesting that effective in vivo inhibition of T3SS with anti-PcrV MAbs is epitope dependent. V2L2MD, while not the most potent MAb as assessed by in vitro cytotoxicity inhibition assays, provided strong prophylactic protection in several murine infection models and a postinfection therapeutic model. V2L2MD mediated significantly (P < 0.0001) better in vivo protection than that provided by a comparator antibody, MAb166, a well-characterized anti-PcrV MAb and the progenitor of a clinical candidate, KB001-A. The results described here support further development of a V2L2MD-containing immunotherapeutic and may suggest even greater potential than was previously recognized for the prevention and treatment of P. aeruginosa infections in high-risk populations.

Management of Pseudomonas aeruginosa pneumonia: one size does not fit all

In view of the mortality associated with Pseudomonas aeruginosa (PSA) ventilator-associated pneumonia (VAP) and the frequency of inadequate initial empiric therapy, recent findings underscore the need for a different management paradigm with effective anti-pseudomonal vaccines for prophylaxis of patients at risk. The association of virulence factors is a variable that splits PSA in two phenotypes, with the possibility of adjunctive immunomodulatory therapy for management of virulent strains. We comment on recent advances in and the state of the art of PSA-VAP management and discuss a new paradigm for tailored and optimal management.

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.

The molecular mechanism of acute lung injury caused by Pseudomonas aeruginosa: from bacterial pathogenesis to host response

Pseudomonas aeruginosa is the most common gram-negative pathogen causing pneumonia in immunocompromised patients. Acute lung injury induced by bacterial exoproducts is associated with a poor outcome in P. aeruginosa pneumonia. The major pathogenic toxins among the exoproducts of P. aeruginosa and the mechanism by which they cause acute lung injury have been investigated: exoenzyme S and co-regulated toxins were found to contribute to acute lung injury. P. aeruginosa secretes these toxins through the recently defined type III secretion system (TTSS), by which gram-negative bacteria directly translocate toxins into the cytosol of target eukaryotic cells. TTSS comprises the secretion apparatus (termed the injectisome), translocators, secreted toxins, and regulatory components. In the P. aeruginosa genome, a pathogenic gene cluster, the exoenzyme S regulon, encodes genes underlying the regulation, secretion, and translocation of TTSS. Four type III secretory toxins, namely ExoS, ExoT, ExoU, and ExoY, have been identified in P. aeruginosa. ExoS is a 49-kDa form of exoenzyme S, a bifunctional toxin that exerts ADP-ribosyltransferase and GTPase-activating protein (GAP) activity to disrupt endocytosis, the actin cytoskeleton, and cell proliferation. ExoT, a 53-kDa form of exoenzyme S with 75% sequence homology to ExoS, also exerts GAP activity to interfere with cell morphology and motility. ExoY is a nucleotidal cyclase that increases the intracellular levels of cyclic adenosine and guanosine monophosphates, resulting in edema formation. ExoU, which exhibits phospholipase A2 activity activated by host cell ubiquitination after translocation, is a major pathogenic cytotoxin that causes alveolar epithelial injury and macrophage necrosis. Approximately 20% of clinical isolates also secrete ExoU, a gene encoded within an insertional pathogenic gene cluster named P. aeruginosa pathogenicity island-2. The ExoU secretory phenotype is associated with a poor clinical outcome in P. aeruginosa pneumonia. Blockade of translocation by TTSS or inhibition of the enzymatic activity of translocated toxins has the potential to decrease acute lung injury and improve clinical outcome.

The anti-Pseudomonas aeruginosa antibody Panobacumab is efficacious on acute pneumonia in neutropenic mice and has additive effects with meropenem

Pseudomonas aeruginosa (P. aeruginosa) infections are associated with considerable morbidity and mortality in immunocompromised patients due to antibiotic resistance. Therefore, we investigated the efficacy of the anti-P. aeruginosa serotype O11 lipopolysaccharide monoclonal antibody Panobacumab in a clinically relevant murine model of neutropenia induced by cyclophosphamide and in combination with meropenem in susceptible and meropenem resistant P. aeruginosa induced pneumonia. We observed that P. aeruginosa induced pneumonia was dramatically increased in neutropenic mice compared to immunocompetent mice. First, Panobacumab significantly reduced lung inflammation and enhanced bacterial clearance from the lung of neutropenic host. Secondly, combination of Panobacumab and meropenem had an additive effect. Third, Panobacumab retained activity on a meropenem resistant P. aeruginosa strain. In conclusion, the present data established that Panobacumab contributes to the clearance of P. aeruginosa in neutropenic hosts as well as in combination with antibiotics in immunocompetent hosts. This suggests beneficial effects of co-treatment even in immunocompromised individuals, suffering most of the morbidity and mortality of P. aeruginosa infections.

Structure and function of the Type III secretion system of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a dangerous pathogen particularly because it harbors multiple virulence factors. It causes several types of infection, including dermatitis, endocarditis, and infections of the urinary tract, eye, ear, bone, joints and, of particular interest, the respiratory tract. Patients with cystic fibrosis, who are extremely susceptible to Pseudomonas infections, have a bad prognosis and high mortality. An important virulence factor of P. aeruginosa, shared with many other gram-negative bacteria, is the type III secretion system, a hollow molecular needle that transfers effector toxins directly from the bacterium into the host cell cytosol. This complex macromolecular machine works in a highly regulated manner and can manipulate the host cell in many different ways. Here we review the current knowledge of the structure of the P. aeruginosa T3SS, as well as its function and recognition by the immune system. Furthermore, we describe recent progress in the development and use of therapeutic agents targeting the T3SS.

PcrV antibody-antibiotic combination improves survival in Pseudomonas aeruginosa-infected mice

The type III secretion system (TTSS) of Pseudomonas aeruginosa, associated with acute infection, facilitates the direct injection of cytotoxins into the host cell cytoplasm. Mab166, a murine monoclonal antibody against PcrV, a protein located at the tip of the injectisome, has demonstrated efficacy against P. aeruginosa infection, resulting in reduced lung injury and increased survival in murine models of infection. We hypothesised that the administration of Mab166 in combination with an antibiotic would further improve the survival of P. aeruginosa-infected mice. A murine model of P. aeruginosa acute infection, three clinically relevant antibiotics (ciprofloxacin, tobramycin and ceftazidime) and the Mab166 antibody were used for this study. Consistently, compared to other treatment groups (antibiotic or antibody administered in isolation), the combination of Mab166 and antibiotic significantly improved the survival of mice infected with three times the lethal dose (LD(90)) of the highly cytotoxic ExoU-secreting strain, PA103. This synergistic effect was primarily due to enhanced bactericidal effect and protection against lung injury, which prevented bacterial dissemination to other organs. Hence, the combination of Mab166 with antibiotic administration provides a new, more effective strategy against P. aeruginosa airway infection, especially when large numbers of highly virulent strains are present.

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.