Systemic, nasal and oral live vaccines against Pseudomonas aeruginosa: A clinical trial of immunogenicity in lower airways of human volunteers

Pseudomonas aeruginosa: Infections, Animal Modeling, and Therapeutics

Pseudomonas aeruginosa is an important Gram-negative opportunistic pathogen which causes many severe acute and chronic infections with high morbidity, and mortality rates as high as 40%. What makes P. aeruginosa a particularly challenging pathogen is its high intrinsic and acquired resistance to many of the available antibiotics. In this review, we review the important acute and chronic infections caused by this pathogen. We next discuss various animal models which have been developed to evaluate P. aeruginosa pathogenesis and assess therapeutics against this pathogen. Next, we review current treatments (antibiotics and vaccines) and provide an overview of their efficacies and their limitations. Finally, we highlight exciting literature on novel antibiotic-free strategies to control P. aeruginosa infections.

Immune responses and protective efficacy of a trivalent combination DNA vaccine based on oprL, oprF and flgE genes of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an infectious pathogenic bacteria infecting many different species of animals. Currently, it lacks a commercial vaccine. In this study, three monovalent DNA vaccines (poprL, poprF, and pflgE), three bivalent combination DNA vaccines (poprL+poprF, poprL+pflgE, poprF+pflgE), and a trivalent DNA vaccine (poprL+poprF+pflgE) were constructed. Consequently, we immunised chickens with these DNA vaccines and used inactivated vaccines as the positive controls. Then, the immune efficacy was evaluated through serum antibody detection, a lymphocyte proliferation assay, and cytokine concentration determination. Lastly, we assessed the protection rate through a challenge experiment. Following vaccination, the serum antibody levels induced using these DNA vaccines were different due to the different coating antigens. In the trivalent combination DNA vaccine group, we established that the lymphocyte proliferation (SI values), IFN-γ, IL-2, and IL-4 levels were significantly higher than those of the other six DNA vaccine groups and the inactivated vaccine group. However, the protection provided was slightly lower than that of the inactivated vaccine and higher than those of other DNA vaccines. The protection rate of poprL, poprF, pflgE, poprL+poprF, poprL+pflgE, poprF+pflgE, poprL+poprF+pflgE, and the inactivated vaccine were 50, 45, 60, 75, 80, 80, 90, and 95%, respectively. The results of this study indicated the trivalent DNA vaccine based on oprL, oprF and flgE genes represents a promising approach for the prevention of Pseudomonas aeruginosa infections.

Pseudomonas aeruginosa: Recent Advances in Vaccine Development

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

Different Methods and Formulations of Drugs and Vaccines for Nasal Administration

Nasal drug delivery is advantageous when compared with other routes of drug delivery as it avoids the hepatic first-pass effect, blood–brain barrier penetration, and compliance issues with parenteral administration. However, nasal administration also has some limitations, such as its low bioavailability due to metabolism on the mucosal surface, and irreversible damage to the nasal mucosa due to the ingredients added into the formula. Moreover, the method of nasal administration is not applicable to all drugs. The current review presents the nasal anatomy and mucosal environment for the nasal delivery of vaccines and drugs, as well as presents various methods for enhancing nasal absorption, and different drug carriers and delivery devices to improve nasal drug delivery. It also presents future prospects on the nasal drug delivery of vaccines and drugs.

Hacking Commensal Bacteria to Consolidate the Adaptive Mucosal Immune Response in the Gut–Lung Axis: Future Possibilities for SARS-CoV-2 Protection

Infectious diseases caused by mucosal pathogens significantly increase mortality and morbidity. Thus, the possibility to target these pathogens at their primary entry points can consolidate protective immunity. Regarding SARS-CoV-2 infection, it has been observed that the upper respiratory mucosa is highly affected and that dysregulation of resident microbiota in the gut–lung axis plays a crucial role in determining symptom severity. Thus, understanding the possibility of eliciting various mucosal and adaptive immune responses allows us to effectively design bacterial mucosal vaccine vectors. Such design requires rationally selecting resident bacterial candidates as potential host carriers, evaluating effective carrier proteins for stimulating an immune response, and combining these two to improve antigenic display and immunogenicity. This review investigated mucosal vaccine vectors from 2015 to present, where a few have started to utilize Salmonella and lactic acid bacteria (LAB) to display SARS-CoV-2 Spike S proteins or fragments. Although current literature is still lacking for its studies beyond in vitro or in vivo efficiency, decades of research into these vectors show promising results. Here, we discuss the mucosal immune systems focusing on the gut–lung axis microbiome and offer new insight into the potential use of alpha streptococci in the upper respiratory tract as a vaccine carrier.

An oral cancer vaccine using a Bifidobacterium vector suppresses tumor growth in a syngeneic mouse bladder cancer model

Cancer immunotherapy using immune-checkpoint inhibitors (ICIs) such as PD-1/PD-L1 inhibitors has been well established for various types of cancer. Monotherapy with ICIs, however, can achieve a durable response in only a subset of patients. There is a great unmet need for the ICI-resistant-tumors. Since patients who respond to ICIs should have preexisting antitumor T cell response, combining ICIs with cancer vaccines that forcibly induce an antitumor T cell response is a reasonable strategy. However, the preferred administration sequence of the combination of ICIs and cancer vaccines is unknown. In this study, we demonstrated that combining an oral WT1 cancer vaccine using a Bifidobacterium vector and following anti-PD-1 antibody treatment eliminated tumor growth in a syngeneic mouse model of bladder cancer. This vaccine induced T cell responses specific to multiple WT1 epitopes through the gut immune system. Moreover, in a tumor model poorly responsive to an initial anti-PD-1 antibody, this vaccine alone significantly inhibited the tumor growth, whereas combination with continuous anti-PD-1 antibody could not inhibit the tumor growth. These results suggest that this oral cancer vaccine alone or as an adjunct to anti-PD-1 antibody could provide a novel treatment option for patients with advanced urothelial cancer including bladder cancer.

Advances in the development of Salmonella-based vaccine strategies for protection against Salmonellosis in humans

Salmonella spp. are important human pathogens globally causing millions of cases of typhoid fever and non‐typhoidal salmonellosis annually. There are only a few vaccines licensed for use in humans which all target Salmonella enterica serovar Typhi. Vaccine development is hampered by antigenic diversity between the thousands of serovars capable of causing infection in humans. However, a number of attenuated candidate vaccine strains are currently being developed. As facultative intracellular pathogens with multiple systems for transporting effector proteins to host cells, attenuated Salmonella strains can also serve as ideal tools for the delivery of foreign antigens to create multivalent live carrier vaccines for simultaneous immunization against several unrelated pathogens. Further, the ease with which Salmonella can be genetically modified and the extensive knowledge of the virulence mechanisms of this pathogen means that this bacterium has often served as a model organism to test new approaches. In this review we focus on (1) recent advances in live attenuated Salmonella vaccine development, (2) improvements in expression of foreign antigens in carrier vaccines and (3) adaptation of attenuated strains as sources of purified antigens and vesicles that can be used for subunit and conjugate vaccines or together with attenuated vaccine strains in heterologous prime‐boosting immunization strategies. These advances have led to the development of new vaccines against Salmonella which have or will soon be tested in clinical trials.

Strategies for Enhancement of Live-Attenuated Salmonella-Based Carrier Vaccine Immunogenicity

The use of live-attenuated bacterial vaccines as carriers for the mucosal delivery of foreign antigens to stimulate the mucosal immune system was first proposed over three decades ago. This novel strategy aimed to induce immunity against at least two distinct pathogens using a single bivalent carrier vaccine. It was first tested using a live-attenuated Salmonella enterica serovar Typhi strain in clinical trials in 1984, with excellent humoral immune responses against the carrier strain but only modest responses elicited against the foreign antigen. Since then, clinical trials with additional Salmonella-based carrier vaccines have been conducted. As with the original trial, only modest foreign antigen-specific immunity was achieved in most cases, despite the incorporation of incremental improvements in antigen expression technologies and carrier design over the years. In this review, we will attempt to deconstruct carrier vaccine immunogenicity in humans by examining the basis of bacterial immunity in the human gastrointestinal tract and how the gut detects and responds to pathogens versus benign commensal organisms. Carrier vaccine design will then be explored to determine the feasibility of retaining as many characteristics of a pathogen as possible to elicit robust carrier and foreign antigen-specific immunity, while avoiding over-stimulation of unacceptably reactogenic inflammatory responses.

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

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

Emerging therapies against infections with Pseudomonas aeruginosa

Infections with Pseudomonas aeruginosa have been marked with the highest priority for surveillance and epidemiological research on the basis of parameters such as incidence, case fatality rates, chronicity of illness, available options for prevention and treatment, health-care utilization, and societal impact. P. aeruginosa is one of the six ESKAPE pathogens that are the major cause of nosocomial infections and are a global threat because of their capacity to become increasingly resistant to all available antibiotics. This review reports on current pre-clinical and clinical advances of anti-pseudomonal therapies in the fields of drug development, antimicrobial chemotherapy, vaccines, phage therapy, non-bactericidal pathoblockers, outer membrane sensitizers, and host defense reinforcement.

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

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

Live-Attenuated Bacterial Vectors for Delivery of Mucosal Vaccines, DNA Vaccines, and Cancer Immunotherapy

Vaccines save millions of lives each year from various life-threatening infectious diseases, and there are more than 20 vaccines currently licensed for human use worldwide. Moreover, in recent decades immunotherapy has become the mainstream therapy, which highlights the tremendous potential of immune response mediators, including vaccines for prevention and treatment of various forms of cancer. However, despite the tremendous advances in microbiology and immunology, there are several vaccine preventable diseases which still lack effective vaccines. Classically, weakened forms (attenuated) of pathogenic microbes were used as vaccines. Although the attenuated microbes induce effective immune response, a significant risk of reversion to pathogenic forms remains. While in the twenty-first century, with the advent of genetic engineering, microbes can be tailored with desired properties.

In this review, I have focused on the use of genetically modified bacteria for the delivery of vaccine antigens. More specifically, the live-attenuated bacteria, derived from pathogenic bacteria, possess many features that make them highly suitable vectors for the delivery of vaccine antigens. Bacteria can theoretically express any heterologous gene or can deliver mammalian expression vectors harboring vaccine antigens (DNA vaccines). These properties of live-attenuated microbes are being harnessed to make vaccines against several infectious and noninfectious diseases. In this regard, I have described the desired features of live-attenuated bacterial vectors and the mechanisms of immune responses manifested by live-attenuated bacterial vectors. Interestingly anaerobic bacteria are naturally attracted to tumors, which make them suitable vehicles to deliver tumor-associated antigens thus I have discussed important studies investigating the role of bacterial vectors in immunotherapy. Finally, I have provided important discussion on novel approaches for improvement and tailoring of live-attenuated bacterial vectors for the generation of desired immune responses.

Anti-bacterial antibody and T cell responses in bronchiectasis are differentially associated with lung colonization and disease

BACKGROUND

As a way to determine markers of infection or disease informing disease management, and to reveal disease-associated immune mechanisms, this study sought to measure antibody and T cell responses against key lung pathogens and to relate these to patients' microbial colonization status, exacerbation history and lung function, in Bronchiectasis (BR) and Chronic Obstructive Pulmonary Disease (COPD).

METHODS

One hundred nineteen patients with stable BR, 58 with COPD and 28 healthy volunteers were recruited and spirometry was performed. Bacterial lysates were used to measure specific antibody responses by ELISA and T cells by ELIspot. Cytokine secretion by lysate-stimulated T cells was measured by multiplex cytokine assay whilst activation phenotype was measured by flow cytometry.

RESULTS

Typical colonization profiles were observed in BR and COPD, dominated by P.aeruginosa, H.influenzae, S.pneumoniae and M.catarrhalis. Colonization frequency was greater in BR, showing association with increased antibody responses against P.aeruginosa compared to COPD and HV, and with sensitivity of 73% and specificity of 95%. Interferon-gamma T cell responses against P.aeruginosa and S.pneumoniae were reduced in BR and COPD, whilst reactive T cells in BR had similar markers of homing and senescence compared to healthy volunteers. Exacerbation frequency in BR was associated with increased antibodies against P. aeruginosa, M.catarrhalis and S.maltophilia. T cell responses against H.influenzae showed positive correlation with FEV₁% (r = 0.201, p = 0.033) and negative correlation with Bronchiectasis Severity Index (r = - 0.287, p = 0.0035).

CONCLUSION

Our findings suggest a difference in antibody and T cell immunity in BR, with antibody being a marker of exposure and disease in BR for P.aeruginosa, M.catarrhalis and H.influenzae, and T cells a marker of reduced disease for H.influenzae.

Vaccines against major ICU pathogens: where do we stand?

PURPOSE OF REVIEW

Multidrug resistance of bacterial pathogens has confronted physicians around the world with the threat of inefficacy of the antibiotic regime, which is particularly important for patients with sepsis. Antibiotic resistance has revived search for alternative nonantibiotic strategies. Among them, prophylaxis by vaccination is an appealing concept.

RECENT FINDINGS

This review provides a compact overview on available vaccines against community-acquired pathogens such as pneumococci (in synergy with influenza) and meningococci and provides an overview on the ongoing developments of vaccines targeting typical nosocomial pathogens such as Clostridium difficile, Staphylococcus aureus, Acintetobacter baumannii, Klebsiella pneumonia, and Pseudomonas aeruginosa.

SUMMARY

The effects achieved by some conjugated vaccines (e.g. against Haemophilus influenzae B and Streptococcus pneumoniae) are encouraging. Their widespread use has resulted in a decrease or almost elimination of invasive diseases by the covered pneumococcal serotypes or Haemophilus influenzae B, respectively. These vaccines confer not only individual protection but also exploit herd protection effects. However, a multitude of failures reflects the obstacles on the way to effective and well tolerated bacterial vaccines. Regional differences in strain prevalence and variability of antigens that limit cross-protectivity remain major obstacles. However, promising candidates are in clinical development.

Live bacterial vaccine vector and delivery strategies of heterologous antigen: A review

Live bacteria, including attenuated bacteria and probiotics, can be engineered to deliver target antigen to excite the host immune system. The preponderance of these live bacterial vaccine vectors is that they can stimulate durable humoral and cellular immunity. Moreover, delivery strategies of heterologous antigen in live bacterial promote the applications of new vaccine development. Genetic technologies are evolving, which potentiate the developing of heterologous antigen delivery systems, including bacterial surface display system, bacterial secretion system and balanced lethal vector system. Although the live bacterial vaccine vector is a powerful adjuvant, certain disadvantages, such as safety risk, must also be taken into account. In this review, we compare the development of representative live bacterial vectors, and summarize the main characterizations of the various delivery strategies of heterologous antigen in live vector vaccines.

Vaccine strategies against cystic fibrosis pathogens

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

Intracellular delivery of biologic therapeutics by bacterial secretion systems

Biologics are a promising new class of drugs based on complex macromolecules such as proteins and nucleic acids. However, delivery of these macromolecules into the cytoplasm of target cells remains a significant challenge. Here we present one potential solution: bacterial nanomachines that have evolved over millions of years to efficiently deliver proteins and nucleic acids across cell membranes and between cells. In this review, we provide a brief overview of the different bacterial systems capable of direct delivery into the eukaryotic cytoplasm and the medical applications for which they are being investigated, along with a perspective on the future directions of this exciting field.

X-ray Irradiated Vaccine Confers protection against Pneumonia caused by Pseudomonas aeruginosa

Pseudomonas aeruginosa is a gram-negative bacterium and one of the leading causes of nosocomial infection worldwide, however, no effective vaccine is currently available in the market. Here, we demonstrate that inactivation of the bacteria by X-ray irradiation inhibits its replication capability but retained antigenic expression functionally thus allowing its use as a potential vaccine. Mice immunized by this vaccine were challenged by the parental strain, the O-antigen-homologous strain PAO-1 (O2/O5) and heterologous strain PAO-6 (O6) in an acute pneumonia model. We further measured the protective effect of the vaccine, as well as host innate and cellular immunity responses. We found immunized mice could protect against both strains. Notably, the antiserum only had significant protective role against similar bacteria, while adoptive transfer of lymphocytes significantly controlled the spread of the virulent heterologous serogroup PAO-6 infection, and the protective role could be reversed by CD4 rather than CD8 antibody. We further revealed that vaccinated mice could rapidly recruit neutrophils to the airways early after intranasal challenge by PAO-6, and the irradiated vaccine was proved to be protective by the generated CD4(+) IL-17(+) Th17 cells. In conclusion, the generation of inactivated but metabolically active microbes is a promising strategy for safely vaccinating against Pseudomonas aeruginosa.

Live-Attenuated Bacterial Vectors: Tools for Vaccine and Therapeutic Agent Delivery

Genetically attenuated microorganisms, including pathogenic and commensal bacteria, can be engineered to carry and deliver heterologous antigens to elicit host immunity against both the vector as well as the pathogen from which the donor gene is derived. These live attenuated bacterial vectors have been given much attention due to their capacity to induce a broad range of immune responses including localized mucosal, as well as systemic humoral and/or cell-mediated immunity. In addition, the unique tumor-homing characteristics of these bacterial vectors has also been exploited for alternative anti-tumor vaccines and therapies. In such approach, tumor-associated antigen, immunostimulatory molecules, anti-tumor drugs, or nucleotides (DNA or RNA) are delivered. Different potential vectors are appropriate for specific applications, depending on their pathogenic routes. In this review, we survey and summarize the main features of the different types of live bacterial vectors and discussed the clinical applications in the field of vaccinology. In addition, different approaches for using live attenuated bacterial vectors for anti-cancer therapy is discussed, and some promising pre-clinical and clinical studies in this field are outlined.

Effect of vaccine administration modality on immunogenicity and efficacy

The many factors impacting the efficacy of a vaccine can be broadly divided into three categories: features of the vaccine itself, including immunogen design, vaccine type, formulation, adjuvant and dosing; individual variations among vaccine recipients and vaccine administration-related parameters. While much literature exists related to vaccines, and recently systems biology has started to dissect the impact of individual subject variation on vaccine efficacy, few studies have focused on the role of vaccine administration-related parameters on vaccine efficacy. Parenteral and mucosal vaccinations are traditional approaches for licensed vaccines; novel vaccine delivery approaches, including needless injection and adjuvant formulations, are being developed to further improve vaccine safety and efficacy. This review provides a brief summary of vaccine administration-related factors, including vaccination approach, delivery route and method of administration, to gain a better understanding of their potential impact on the safety and immunogenicity of candidate vaccines.

Mucosal vaccination by the intranasal route. Nose-associated lymphoid tissue (NALT)-Structure, function and species differences

The advantage of mucosal vaccination in viral and bacterial infections in different age groups is of enormous clinical relevance. The advantages and potential hazards of intranasal vaccination have always to be considered. The intranasal route for vaccination is very successful for some antigens. Specific adjuvants are necessary. In the nose of rodents there is a structured lymphoid tissue (nose-associated lymphoid tissue (NALT)). This abbreviation should not be used for nasopharynx-associated lymphoid tissue, as this includes parts of the tonsils. In children lymphoid tissue is more dispersed in the nose and not concentrated at the bottom of the dorsal nose ducts as in rodents. There are no data on organized lymphoid tissue in the nose of adults. In NALT of rodents there is a unique structure of adhesion molecule expression; the postnatal development and the different composition of T and B lymphocytes in comparison with Peyer's patches document the uniqueness of this lymphoid organ. There is also a mucosa in the nose with antigen-presenting dendritic cells. Thus, it is often unclear whether intranasal vaccination is initiated via NALT or the diffuse nasal mucosa. There are still many open questions e. g., which adjuvant is necessary for a specific virus, bacterium or other allergen, how many doses are critical for an effective nasal vaccination. Species differences are of major importance when extrapolating results from rodents to humans.

Live bacterial vaccine vectors: an overview

Genetically attenuated microorganisms, pathogens, and some commensal bacteria can be engineered to deliver recombinant heterologous antigens to stimulate the host immune system, while still offering good levels of safety. A key feature of these live vectors is their capacity to stimulate mucosal as well as humoral and/or cellular systemic immunity. This enables the use of different forms of vaccination to prevent pathogen colonization of mucosal tissues, the front door for many infectious agents. Furthermore, delivery of DNA vaccines and immune system stimulatory molecules, such as cytokines, can be achieved using these special carriers, whose adjuvant properties and, sometimes, invasive capacities enhance the immune response. More recently, the unique features and versatility of these vectors have also been exploited to develop anti-cancer vaccines, where tumor-associated antigens, cytokines, and DNA or RNA molecules are delivered. Different strategies and genetic tools are constantly being developed, increasing the antigenic potential of agents delivered by these systems, opening fresh perspectives for the deployment of vehicles for new purposes. Here we summarize the main characteristics of the different types of live bacterial vectors and discuss new applications of these delivery systems in the field of vaccinology.

Antigen Delivery System II

This chapter reviews papers mostly written since 2005 that report results using live attenuated bacterial vectors to deliver after administration through mucosal surfaces, protective antigens, and DNA vaccines, encoding protective antigens to induce immune responses and/or protective immunity to pathogens that colonize on or invade through mucosal surfaces. Papers that report use of such vaccine vector systems for parenteral vaccination or to deal with nonmucosal pathogens or do not address induction of mucosal antibody and/or cellular immune responses are not reviewed.

Intranasal immunisation of the recombinant Toxoplasma gondii receptor for activated C kinase 1 partly protects mice against T. gondii infection

Nasal vaccination is an effective therapeutic regimen for preventing certain infectious diseases. The mucosal immune response is important for resistance to Toxoplasma gondii infection. In this study, we evaluated the immune responses elicited in BALB/c mice by nasal immunisation with recombinant T. gondii receptor for activated C kinase 1 (rTgRACK1) and their protective efficacy against T. gondii RH strain during both chronic and lethal infections. Nasal vaccination with rTgRACK1 increased the level of secretory IgA in nasal, intestinal and vesical washes, and the level of IFN-γ and IL-2 in intestinal washes, indicating that rTgRACK1 vaccination promotes mucosal immune responses. The mice immunised with rTgRACK1 also displayed increased levels of rTgRACK1-specific IgA, total IgG, IgG1 and in particular IgG2a in their blood sera, increased production of IFN-γ, IL-2 and IL-4 but not IL-10 from their isolated spleen cells, and enhanced splenocyte proliferation in vitro. rTgRACK1-vaccinated mice were effectively protected against infection with T. gondii RH strain, showing over 50% reduction of tachyzoite burdens in their liver and brain tissues during a chronic infection, and also a 45% increase in their survivals during a lethal challenge. These results indicate that rTgRACK1 might represent an intriguing immunogen for developing a mucosal vaccine against toxoplasmosis.

New perspectives in the management of Pseudomonas aeruginosa infections

ABSTRACT: 

Infections with Pseudomonas aeruginosa are a major health problem, especially for immune-compromised and cystic fibrosis patients, owing to the particular drug resistance of the microorganism. The aim of this review is to provide recent insights into strategies under investigation for prevention and therapy of these infections. In this survey, the approach directed against bacterial biofilm formation and quorum-sensing systems was focused, along with the evaluation of the treatment with bacteriophages. New interesting, developmental studies and clinical trials to prevent or treat infections due to this opportunistic pathogen are based on active and passive immunotherapy. Some monoclonal antibodies and different vaccines against this microorganism have been developed in the last few decades, even though to date none of them have obtained market authorization.

Salmonella as a vaccine delivery vehicle

Attenuated Salmonella vaccines can be administered orally to deliver recombinant antigens to mucosal surfaces inducing a protective immune response against a variety of targeted pathogens. A number of exciting new approaches and technologies for attenuated Salmonella vaccines have been developed recently. However, a disconnect remains between results obtained with mice in preclinical studies and results obtained in human clinical trials. This is due to an incomplete understanding of Salmonella Typhi interactions with human hosts and inadequate animal models available for study. In this review, the authors describe recent progress in identifying important differences underlying S. Typhi-host interactions, the development of novel approaches to vaccine design and six recent clinical trials evaluating Salmonella-vectored vaccines.

Immunoproteomics: the key to discovery of new vaccine antigens against bacterial respiratory infections

The increase in antibiotic resistance and the shortage of new antimicrobials to prevent difficult bacterial infections underlines the importance of prophylactic therapies to prevent infection by bacterial pathogens. Vaccination has reduced the incidence of many serious diseases, including respiratory bacterial infections. However, there are many pathogens for which no vaccine is available and some vaccines are not effective among all age groups or among immunocompromised individuals. Immunoproteomics is a powerful technique which has been used to identify potential vaccine candidates to protect against pathogenic bacteria. The combination of proteomics with the detection of immunoreactive antigens using serum highlights immunogenic proteins that are expressed during infection. This is particularly useful when patient serum is used as the antigens that promote a humoral response during human infection are identified. This review outlines examples of vaccine candidates that have been identified using immunoproteomics and have successfully protected animals against challenge when tested in immunisation studies. Many immunoreactive proteins are common to several unrelated pathogens, however some of these are not always protective in animal immunisation and challenge studies. Furthermore, examples of well-established immunogens, including Bordetella pertussis antigen FHA were not detected in immunoproteomics studies, indicating that this technology may underrepresent the immunoreactive proteins in a pathogen. Although only one step in the pathway towards an efficacious approved vaccine, immunoproteomics is an important technology in the identification of novel vaccine antigens.

A randomized, placebo-controlled phase I study assessing the safety and immunogenicity of a Pseudomonas aeruginosa hybrid outer membrane protein OprF/I vaccine (IC43) in healthy volunteers

INTRODUCTION

IC43 is a recombinant outer membrane protein-based vaccine against Pseudomonas aeruginosa (P. aeruginosa) consisting of OprF- and OprI- epitopes (Opr, outer membrane protein; OprF/I, OprF/OprI hybrid vaccine) with an N-terminal His 6 tag (Met-Ala-(His)6-OprF190-342-OprI21-83).

OBJECTIVES

The study aimed to confirm the optimal dose of IC43 in adults with regard to immunogenicity, safety, and tolerability after vaccination with three different dosages of IC43, compared with placebo, and to investigate a potential immune-enhancing effect of the adjuvant, aluminum hydroxide. Subjects were randomly allocated in a 1:1:1:1:1 ratio to one of five treatment groups: 50, 100, or 200 µg IC43 with adjuvant, 100 µg IC43 without adjuvant, or placebo (0.9% sodium chloride) and two intramuscular injections were given in the deltoid region 7 d apart.

RESULTS

The primary immunogenicity analysis of OprF/I-specific IgG antibody titers on day 14 demonstrated statistically significant differences among treatment groups (P<0.0001), with a significantly higher immune response detected in each IC43 treatment group compared with placebo. From day 0 to day 14, a ≥4-fold increase in OprF/I-specific immunoglobulin G (IgG) antibody titers were observed in>90% of subjects in all IC43 treatment groups in the per-protocol (PP) and intention-to-treat (ITT) populations; a ≥50-fold titer increase was observed in 42.6% subjects including all IC43 treatment groups. On day 90, OprF/I-specific IgGs started to decline in all IC43 treatment groups but remained significantly higher until 6 mo compared with placebo. Assessment of functional antibody induction by opsonophagocytic assay (OPA) followed a similar pattern compared with OprF/I-specific IgG kinetics. At day 14, a ≥2-fold increase in OPA titer was observed in 54.5% subjects within all IC43 treatment groups. An increase in antibody avidity index was observed after the second vaccination. At day 14, >96% of subjects in each IC43 treatment group had detectable OprF/I-specific IgG antibodies. Anti-histidine IgG antibody titers peaked on day 14 and were reduced on day 90 in all IC43 treatment groups. OprF/I-specific IgG secreted by antibody-secreting cell (ASC) was detected in all IC43 groups by B-cell ELIspot after the second vaccination and up to 6 mo. All vaccinations were safe and well tolerated up to the maximum cumulative dosage of 400 µg IC43.

CONCLUSION

IC43 doses equal to or greater than 50 µg were sufficient to induce a plateau of IgG antibody responses in healthy volunteers. Higher doses, whether adjuvanted or non-adjuvanted, were not more effective.

METHODS

In this phase I, randomized, placebo-controlled, observer-blinded, multicenter clinical trial, 163 healthy volunteers (18-65 y) were randomly assigned to five treatment groups (1:1:1:1:1). Three groups received IC43 with adjuvant: 50 µg (n=32), 100 µg (n=33), or 200 µg (n=33). One group received IC43 100 µg without adjuvant (n=32), and one group received placebo (0.9% sodium chloride) (n=33). Each subject received two intramuscular vaccinations, separated by a 7-d interval (days 0 and 7) (Fig. 1). Humoral immune response was assessed by measurement of outer membrane protein F/I (OprF/I)-specific antibodies determined by enzyme-linked immunosorbent assay (ELISA), anti-histidine antibodies determined by ELISA, and functional antibody activity determined by opsonophagocytic assay (OPA), up to 6 mo post-vaccination. Antibody avidity was measured on days 7 and 14 from samples that had detectable vaccine antibody-specific immunoglobulin G (IgG) antibody titers. At the Austrian site only, the B-cell ELIspot assay was used to determine specific ASC responses. Safety was assessed using adverse event monitoring and clinical laboratory tests. Local and systemic tolerability was recorded in a subject diary for 7 d after each vaccination and by investigators up to 6 mo post-vaccination.

Mucosal and systemic antibody responses to potential Pseudomonas aeruginosa vaccine protein antigens in young children with cystic fibrosis following colonization and infection

Pseudomonas aeruginosa is an important prognostic determinant in cystic fibrosis (CF). Little is known however, about P. aeruginosa induced local mucosal and systemic immune responses. Twenty CF children were categorized according to their P. aeruginosa status: (1) chronic lower respiratory tract infection (LRTI), (2) prior successfully treated initial LRTI, (3) isolated upper respiratory tract (URT) colonization, and (4) no known URT colonization or previous LRTI. Their antibody responses, and those of six non-CF disease controls, in serum and bronchoalveolar lavage (BAL) fluid to potential P. aeruginosa vaccine antigens outer membrane protein F (OprF), outer membrane protein H (OprH), catalase A (KatA) and a whole killed cell (WKC) extract were evaluated. Outer membrane protein G (OprG) responses were also measured in blood. Natural exposure, colonization and infection resulted in detectable antibody levels in BAL and serum in all CF groups. Both chronically infected and URT colonized CF children had substantially elevated immunoglobulin A antibody levels in the BAL fluid and sera toward the WKC extract and OprF antigen compared with the other groups of CF children and non-CF controls. The serum levels of specific P. aeruginosa antibodies involving immunoglobulin G and M isotypes increased with chronic LRTI, especially antibody levels to KatA, OprH and WKC extract, which were substantially greater in chronically infected children compared with all other groups. In conclusion, natural exposure, URT colonization and LRTI with P. aeruginosa all induce substantial mucosal and systemic antibody responses to potential vaccine antigens with chronically infected CF children having the highest levels.

Mucosal immunity and nasal influenza vaccination

Influenza remains a threat to public health, with immunization being a suitable method of infection prevention and control. Our understanding of the immunological regulations at the mucosa, antigen processing and presentation, and B-cell activation has improved, enabling research and targeted induction of immune responses at the site of antigen delivery. Nasal influenza immunization has distinct features compared with intramuscular vaccines, providing protection at the pathogen's entry site, higher levels of mucosal antibodies, cross-protection and needle-free application. This review summarizes our knowledge about mucosal immunity and the experience from clinical trials on the impact and safety of nasal influenza vaccination.

Two mucosal-parenteral schedules to coadminister a multiantigenic formulation against HIV-1 in Balb/c mice

Previous studies showed that simultaneous immunization through the nasal (IN) and subcutaneous (SC) route of a multiantigenic formulation induced a Th1 anti-HIV humoral and cellular immune responses. The formulation was comprised of a recombinant protein of HIV-1 (named CR3; Cellular Response number 3) and the surface and nucleocapsid antigens of hepatitis B virus. This study asks whether four times simultaneous administration through the IN and SC routes (SC+IN) of the multiantigenic formulation induces a similar systemic and mucosal immune responses than two sequential IN priming and two SC boosting (2IN&2SC) inoculations in mice. To answer this question, we tested the same total dose of each antigen per animal in both schedules of inoculation. We found that SC+IN and 2IN&2SC coadministration induced comparable levels of CR3(HIV)-specific IFN-γ-secreting cells and CD8+ cells proliferation in the systemic compartment of animals. Consistent with these findings, a similar Th1 profile considering anti-CR3 IgG1:IGg2a ratio was observed. Additionally, the level of IgG antibodies and the frequency of seroconverting animals in vagina were not different. However, in the case of IgA antibodies the same parameters were significantly higher in the SC+IN group. We also found important level of HBsAg-specific antibodies in serum and vaginal washes.

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.

Multi-Functional Characteristics of the Pseudomonas aeruginosa Type III Needle-Tip Protein, PcrV; Comparison to Orthologs in other Gram-negative Bacteria

Pseudomonas aeruginosa possesses a type III secretion system (T3SS) to intoxicate host cells and evade innate immunity. This virulence-related machinery consists of a molecular syringe and needle assembled on the bacterial surface, which allows delivery of T3 effector proteins into infected cells. To accomplish a one-step effector translocation, a tip protein is required at the top end of the T3 needle structure. Strains lacking expression of the functional tip protein fail to intoxicate host cells. P. aeruginosa encodes a T3S that is highly homologous to the proteins encoded by Yersinia spp. The needle-tip proteins of Yersinia, LcrV, and P. aeruginosa, PcrV, share 37% identity and 65% similarity. Other known tip proteins are AcrV (Aeromonas), IpaD (Shigella), SipD (Salmonella), BipD (Burkholderia), EspA (EPEC, EHEC), Bsp22 (Bordetella), with additional proteins identified from various Gram-negative species, such as Vibrio and Bordetella. The tip proteins can serve as a protective antigen or may be critical for sensing host cells and evading innate immune responses. Recognition of the host microenvironment transcriptionally activates synthesis of T3SS components. The machinery appears to be mechanically controlled by the assemblage of specific junctions within the apparatus. These junctions include the tip and base of the T3 apparatus, the needle proteins and components within the bacterial cytoplasm. The tip proteins likely have chaperone functions for translocon proteins, allowing the proper assembly of translocation channels in the host membrane and completing vectorial delivery of effector proteins into the host cytoplasm. Multi-functional features of the needle-tip proteins appear to be intricately controlled. In this review, we highlight the functional aspects and complex controls of T3 needle-tip proteins with particular emphasis on PcrV and LcrV.

Diagnostic value of antibodies against Pseudomonas aeruginosa in bronchoalveolar lavage fluid after lung transplantation

BACKGROUND

Pseudomonal airway colonization is a risk factor for chronic allograft dysfunction after lung transplantation (LTx). Pseudomonas aeruginosa exoproteases are involved in initiating colonization, and immune complexes directed against these proteases may activate innate immune responses.

OBJECTIVE

To investigate whether specific antibodies against pseudomonal proteases could be measured in bronchoalveolar lavage (BAL) fluid, whether they are associated with innate immune responses, and whether they could identify patients with chronic P. aeruginosa colonization after LTx.

MATERIALS AND METHODS

BAL fluid from 40 noncolonized and 25 chronically colonized LTx recipients was retrospectively assayed for IgG antibodies against P. aeruginosa alkaline protease (AP), elastase (Ela), and exotoxin (Exo), and for BAL total and differential cell counts and IL-8 protein concentration.

RESULTS

BAL anti-Ela and anti-Exo antibody titers were significantly increased in colonized compared with noncolonized patients (P = .009 and P = .02, respectively), whereas anti-AP titers were comparable (P = .79). Antibody titers strongly correlated with each other, and anti-Ela and anti-Exo titers, but not anti-AP titers, also correlated with BAL total cellularity, neutrophilia, and IL-8 protein concentration. Anti-Ela antibodies demonstrated the greatest diagnostic value in receiver operating characteristic analysis to detect chronic airway colonization (P = .009), followed by anti-Exo (P = .02) and anti-AP (P = .79). A combination of all 3 antibodies resulted in overall sensitivity of 45% (95% confidence interval [CI], 29.3-61.5), specificity of 88% (95% CI, 68.8-97.5), and positive predictive value of 55% (95% CI, 38.5-70.7).

CONCLUSION

P. aeruginosa proteases in BAL may be associated with local innate immune responses, and could have the potential to enable detection of chronic colonization after LTx.

Opportunities and challenges of the pulmonary route for vaccination

INTRODUCTION

The respiratory tract is an attractive target for the delivery of vaccine antigens. Potential advantages of drug delivery by means of the pulmonary route include accessibility, non-invasiveness, ease of administration, and the possibility to reach an elaborate mucosal network of antigen-presenting cells.

AREAS COVERED

This review discusses current pulmonary vaccination strategies and their advantages and disadvantages.

EXPERT OPINION

To improve efficiency of vaccination and develop new strategies, a well-founded knowledge about composition and characterization of antigen-presenting cell populations throughout the respiratory tract is essential. In particular, respiratory tract dendritic cells, as key antigen-presenting cells in the lung, constitute an ideal target for vaccine delivery. Furthermore, particle size is a key factor when designing new inhalable vaccines, as size determines not only deposition in different respiratory tract compartments, but also how an antigen and its carrier will interact with lung tissue components and immune cells. An increased knowledge of different respiratory tract antigen-presenting cell populations and their interactions with other components of the immune system will enable new targeting strategies to improve the efficacy of pulmonary vaccination.

Protective anti-Pseudomonas aeruginosa humoral and cellular mucosal immunity by AdC7-mediated expression of the P. aeruginosa protein OprF

Replication-deficient adenoviral (Ad) vectors are an attractive platform for a vaccine against lung infections caused by Pseudomonas aeruginosa. Ad vectors based on non-human serotypes have been developed to circumvent the problem of pre-existing anti-Ad immunity in humans. The present study analyzes the anti-P. aeruginosa systemic and lung mucosal immunity elicited by a non-human primate-based AdC7 vector expressing the outer membrane protein F (AdC7OprF) of P. aeruginosa. Intramuscular immunization of mice with AdC7OprF induced similar levels of serum and mucosal anti-OprF IgG and increased levels of anti-OprF IgA in lung epithelial lining fluid (ELF) compared to immunization with a human serotype Ad5OprF vector (p>0.05). OprF-specific INF-γ in splenic T cells stimulated with OprF-pulsed syngeneic splenic dendritic cells (DC) was similar following immunization with AdC7OprF compared to Ad5OprF (p>0.05). In contrast, OprF-specific INF-γ responses in lung T cells stimulated with either spleen or lung DC were increased following immunization with AdC7OprF compared to Ad5OprF (p<0.05). Interestingly, direct administration of AdC7OprF to the respiratory tract resulted in an increase of OprF-specific IgG in serum, OprF-specific IgG and IgA in lung ELF, and OprF-specific INF-γ in lung T-cells compared to immunization with Ad5OprF, and survival following challenge with a lethal dose of P. aeruginosa. These data demonstrate that systemic or lung mucosal immunization with an AdC7-based vaccine vector induces superior pulmonary humoral and cellular anti-transgene immunity compared to immunization with an Ad5-based vector and favors AdC7-based vectors as vaccines to induce lung mucosal immunity.