Enzyme-linked immunosorbent assay to evaluate the immunogenicity of a polyvalent Klebsiella capsular polysaccharide vaccine in humans

Klebsiella pneumoniae Lipopolysaccharide as a Vaccine Target and the Role of Antibodies in Protection from Disease

Klebsiella pneumoniae is well recognized as a serious cause of infection in healthcare-associated settings and immunocompromised individuals; however, accumulating evidence from resource-limited nations documents an alarming rise in community-acquired K. pneumoniae infections, manifesting as bacteremia and pneumonia as well as neonatal sepsis. The emergence of hypervirulent and antibiotic-resistant K. pneumoniae strains threatens treatment options for clinicians. Effective vaccination strategies could represent a viable alternative that would both preempt the need for antibiotics to treat K. pneumoniae infections and reduce the burden of K. pneumoniae disease globally. There are currently no approved K. pneumoniae vaccines. We review the evidence for K. pneumoniae lipopolysaccharide (LPS) as a vaccine and immunotherapeutic target and discuss the role of antibodies specific for the core or O-antigen determinants within LPS in protection against Klebsiella spp. disease. We expand on the known role of the Klebsiella spp. capsule and O-antigen modifications in antibody surface accessibility to LPS as well as the in vitro and in vivo effector functions reported for LPS-specific antibodies. We summarize key hypotheses stemming from these studies, review the role of humoral immunity against K. pneumoniae O-antigen for protection, and identify areas requiring further research.

Glycoconjugate vaccines against antimicrobial resistant pathogens

INTRODUCTION

Antimicrobial resistance (AMR) is responsible for the death of millions worldwide and stands as a major threat to our healthcare systems, which are heavily reliant on antibiotics to fight bacterial infections. The development of vaccines against the main pathogens involved is urgently required as prevention remains essential against the rise of AMR.

AREAS COVERED

A systematic research review was conducted on MEDLINE database focusing on the six AMR pathogens defined as ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Escherichia coli), which are considered critical or high priority pathogens by the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC). The analysis was intersecated with the terms carbohydrate, glycoconjugate, bioconjugate, glyconanoparticle, and multiple presenting antigen system vaccines.

EXPERT OPINION

Glycoconjugate vaccines have been successful in preventing meningitis and pneumoniae, and there are high expectations that they will play a key role in fighting AMR. We herein discuss the recent technological, preclinical, and clinical advances, as well as the challenges associated with the development of carbohydrate-based vaccines against leading AMR bacteria, with focus on the ESKAPE pathogens. The need of innovative clinical and regulatory approaches to tackle these targets is also highlighted.

Production of a Promising Biosynthetic Self-Assembled Nanoconjugate Vaccine against Klebsiella Pneumoniae Serotype O2 in a General Escherichia Coli Host

Klebsiella pneumoniae has emerged as a severe opportunistic pathogen with multiple drug resistances. Finding effective vaccines against this pathogen is urgent. Although O-polysaccharides (OPS) of K. pneumoniae are suitable antigens for the preparation of vaccines given their low levels of diversity, the low immunogenicity (especially serotype O2) limit their application. In this study, a general Escherichia coli host system is developed to produce a nanoscale conjugate vaccine against K. pneumoniae using the Nano-B5 self-assembly platform. The experimental data illustrate that this nanoconjugate vaccine can induce an efficient humoral immune response in draining lymph nodes (dLNs) and elicit high titers of the IgG antibody against bacterial lipopolysaccharide (LPS). The ideal prophylactic effects of these nanoconjugate vaccines are further demonstrated in mouse models of both systemic and pulmonary infection. These results demonstrate that OPS with low immunogenicity can be changed into an effective antigen, indicating that other haptens may be applicable to this strategy in the future. To the knowledge, this is the first study to produce biosynthetic nanoconjugate vaccines against K. pneumoniae in E. coli, and this strategy can be applied to the development of other vaccines against pathogenic bacteria.

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

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

Prophylaxis and Treatment against Klebsiella pneumoniae: Current Insights on This Emerging Anti-Microbial Resistant Global Threat

Klebsiella pneumoniae (Kp) is an opportunistic pathogen and the leading cause of healthcare-associated infections, mostly affecting subjects with compromised immune systems or suffering from concurrent bacterial infections. However, the dramatic increase in hypervirulent strains and the emergence of new multidrug-resistant clones resulted in Kp occurrence among previously healthy people and in increased morbidity and mortality, including neonatal sepsis and death across low- and middle-income countries. As a consequence, carbapenem-resistant and extended spectrum β-lactamase-producing Kp have been prioritized as a critical anti-microbial resistance threat by the World Health Organization and this has renewed the interest of the scientific community in developing a vaccine as well as treatments alternative to the now ineffective antibiotics. Capsule polysaccharide is the most important virulence factor of Kp and plays major roles in the pathogenesis but its high variability (more than 100 different types have been reported) makes the identification of a universal treatment or prevention strategy very challenging. However, less variable virulence factors such as the O-Antigen, outer membrane proteins as fimbriae and siderophores might also be key players in the fight against Kp infections. Here, we review elements of the current status of the epidemiology and the molecular pathogenesis of Kp and explore specific bacterial antigens as potential targets for both prophylactic and therapeutic solutions.

Klebsiella pneumoniae capsule polysaccharide as a target for therapeutics and vaccines

Carbapenem-resistant (CR) Klebsiella pneumoniae has emerged as an urgent public health threat in many industrialized countries worldwide, including the United States. Infections caused by CR K. pneumoniae are difficult to treat because these organisms are typically resistant to multiple antibiotics, and the patients have significant comorbidities. Notably, there is high (∼50%) mortality among individuals with bacteremia caused by CR K. pneumoniae. Given the dearth of new antibiotics, and the recent convergence of multidrug resistance and hypervirulence, there is a critical need for alternative strategies for the treatment of CR K. pneumoniae infections. The capsule polysaccharide (CPS) of K. pneumoniae has long been viewed as an important virulence factor that promotes resistance to phagocytosis and serum bactericidal activity. Thus, the CPS has been targeted previously for the development of therapeutics and vaccines, although there is no licensed CPS-based vaccine or therapy for the treatment of CR K. pneumoniae infections. Here, we discuss immunoprophylactic and immunotherapeutic approaches that have been tested previously for the treatment of Klebsiella infections. We also suggest potential strategies to promote development of CPS-based vaccines and therapies for prevention and treatment of CR K. pneumoniae infections.

Progress towards the development of Klebsiella vaccines

Introduction: Klebsiella pneumoniae (KP) are a leading cause of healthcare-associated infections. The dramatic increase in microbial resistance to third-generation cephalosporin and carbapenem 'front line' antimicrobial agents and the paucity of new antimicrobials have left clinicians with few therapeutic options and resulted in increased morbidity and mortality. Vaccines may reduce the incidence of infections thereby reducing the necessity for antimicrobials and are not subject to antimicrobial resistance mechanisms. Areas covered: We review whole cell, subunit, capsular polysaccharide (CPS), O polysaccharide (OPS) and conjugate vaccines against KP infection, as well as alternative KP vaccine platforms. Expert opinion: Vaccine-induced antibodies to KP CPS have been protective in preclinical studies, but the number of CPS types (>77) makes vaccines against this virulence factor less feasible. Since four OPS serotypes account of ~80% of invasive KP infections and anti-OPS antibodies are also protective in preclinical studies, both OPS-based conjugate and multiple antigen presenting system (MAPS) vaccines are in active development. Vaccines based on other KP virulence factors, such as outer membrane proteins, type 3 fimbriae (MrkA) and siderophores are at earlier stages of development. Novel strategies for the clinical testing of KP vaccines need to be developed.

Development of immunization trials against Klebsiella pneumoniae

Klebsiella pneumoniae is the most common cause of nosocomial respiratory tract and premature intensive care infections, and the second most frequent cause of Gram-negative bacteraemia and urinary tract infections. Drug resistant isolates remain an important hospital-acquired bacterial pathogen, add significantly to hospital stays, and are especially problematic in high impact medical areas such as intensive care units. Many investigations worldwide proved the increasing resistance of such pathogen, resulting in an average rate of 1.63 outbreak every year. A variety of preventive measures were applied to reduce such incidences. Immunotherapy and passive immunization researches as well found their way to the treatment of Klebsiella. During the last 40 years, many trials for constructing effective vaccines were followed. This up-to-date review classifies such trials and documents them in a progressive way. A following comment discusses each group benefits and defects.

Proinflammatory cytokines in antilipopolysaccharide immunity against Klebsiella infections

This study was undertaken in order to determine whether proinflammatory cytokines are involved in a previously described protection against Klebsiella infection mediated by antilipopolysaccharide antibodies. BALB/c mice were infected intraperitoneally with a lethal challenge of Klebsiella pneumoniae Caroli. One group of mice was protected with monoclonal antibodies against lipopolysaccharide prior to infection and the second was not. We determined the number of colony-forming units at different time points in the blood of infected animals and paralleled them with plasma levels of five proinflammatory cytokines measured by enzyme immunoassays. Our results show that the two groups of animals tested expressed different plasma concentrations for all cytokines. The greatest difference was detected 24 hours after infection, with a higher production in the unprotected group. We concluded that a reduced cytokine production is partially responsible for the survival of protected animals.

Unusual persistence in healthy volunteers and ill patients of hyperimmune immunoglobulin directed against multiple Pseudomonas O-chain and Klebsiella serotypes after intravenous infusion

Persistence of intravenous (i.v.) hyperimmune immunoglobulin (100 mg/kg) directed against clinically predominant serotypes of Pseudomonas and Klebsiella in ill, febrile patients was compared to healthy volunteers to determine if ill patients have a decreased Ig half-life resulting in an increased immunoglobulin requirement. Type-specific antibodies were measured by ELISA for 83 days in eight healthy volunteers and for 35 days in eight ill patients with surgical complications or hematologic malignancy. Mean values and fold rises of antibody concentrations for the two groups were above preinfusion values at 35 days. The antibody fold rises in patients and in healthy volunteers were similar. Type-specific antibody levels in some patients increased after illness coincident with elevation of total immunoglobulins. We conclude that the duration of potentially therapeutic levels of infused type-specific hyperimmune immunoglobulin may persist for a longer period of time than what has been measured for total immunoglobulin. While the mechanism of this persistence remains to be characterized, the possibility of type-specific antibody synthesis induced by immunoglobulin administration must be considered.

Bacterial Polysaccharides as Vaccines — Immunity and Chemical Characterization

Studies on protective immunity and biochemical characterization of bacterial capsular polysaccharides have led to significant contributions to understanding of the mechanisms of infectious diseases and development of effective vaccines. Immunity to encapsulated bacteria is related to antibody response to polysaccharide (PS) antigen, interactions with T- and B-lymphocytes, and host defense mechanisms. Meningococcal, pneumococcal and Salmonella vi PSs and Haemophilus type b PS-protein conjugate vaccines have been licensed and provided effective immunity for prevention of these bacterial infections. Capsular PSs are cell-surface polymers consisting of oligosaccharide repeating units. Many PSs are highly polar and hydrophilic and interfere with cell-to-cell interactions with phagocytes. Most pneumococcal PSs are negatively charged and possess acidic components such as D-glucuronic acid and phosphate in phosphodiester bonds. Extensive immunologic cross-reactivity has been observed among bacterial capsular PSs. In infants the antibody responses to most capsular PSs are generally poor. Enhanced immunogenicity of PS antigens can be achieved through PS-protein conjugate vaccines, immunization during a critical period of perinatal development and effective antigen delivery system.

Solid supports in enzyme-linked immunosorbent assay and other solid-phase immunoassays

A very large proportion of modern immunoassays involve the use of synthetic solid phases to immobilize one of the reactants. These solid-phase immunoassays (SPIs) therefore involve ligand-receptor interactions that occur within a reaction volume close to the solution/solid phase interface. As a consequence, the immunochemistry/biochemistry of these ligand-receptor interactions differs from that of their counterparts in solution. Furthermore, the immobilization process can significantly alter the biological activity of the reactant; most adsorbed proteins on polystyrene or silicone are partially or largely denatured. Therefore the use of alternative methods of immobilization is attractive but may result in little increase in the amount of total functional reactant. However, all commonly used solid phases do not have the same properties or the same capacity for reactant immobilization or experience the same level of nonspecific binding. Empiricism plays a major role in SPIs. Derivations of mass law equations for measuring the antigen capture of solid-phase antibodies, for determining the affinity of solid phase for protein adsorption, and for estimating antibody affinity are reviewed.

O-antigen seroepidemiology of Klebsiella clinical isolates and implications for immunoprophylaxis of Klebsiella infections

To provide a database for the development of an O-antigen-polysaccharide-containing vaccine against Klebsiella spp., we examined the O-antigen seroepidemiology of 378 Klebsiella clinical isolates collected prospectively in two university centers. Strains were typed by competitive enzyme-linked immunosorbent assay with rabbit antisera specific for serogroups O1 to O12 and monoclonal antibodies (MAbs) specific for serogroups O1, O2ab, O2ac, and the genus-specific core antigen. The numbers of isolates (percentages) of individual O serogroups were as follows: 148 (39.2) for serogroup O1, 40 (10.6) for serogroup O2ab, 4 (1.1) for serogroup O2ac, 89 (23.6) for serogroup O3, 2 (0.5) for serogroup O4, 32 (8.5) for serogroup O5, none for serogroups O7, O9, and O12, and 21 (5.6) for serogroup O11. Forty-two (11.1) of the strains were non-O-typeable. O-serogroup distributions were virtually identical between isolates from invasive infections and those from noninvasive infections or colonizations. A vaccine containing the O-specific polysaccharides of serogroups O1, O2ab, O3, and O5 would cover 82% of clinically occurring O-antigen specificities. Three hundred thirty-eight of 378 isolates (89.4%) reacted with the genus-specific MAb V/9-5, which recognizes an epitope of the outer core region of Klebsiella lipopolysaccharide. Antibodies directed against this epitope may represent a further alternative for O-antigen-targeted immunoprophylaxis of Klebsiella infections. These data support further experimental investigations on the protective potential of O-antigen-based vaccines and/or hyperimmune globulins in Klebsiella infection.

Phase 1 trial of a 24-valent Klebsiella capsular polysaccharide vaccine and an eight-valent Pseudomonas O-polysaccharide conjugate vaccine administered simultaneously

A Klebsiella (K) vaccine consisting of 24 capsular polysaccharide antigens and a Pseudomonas aeruginosa (P) vaccine consisting of eight O-polysaccharide antigens conjugated to P toxin A have been developed to prevent sepsis by means of active or passive immunoprophylaxis. In search for a practical immunization schedule, the two vaccines were injected in opposite arms simultaneously (20 volunteers) or 14 days apart (21 volunteers). The vaccines were similarly well tolerated by both volunteer groups. Geometric mean antibody concentrations and mean fold antibody rises to the 33 vaccine antigens (including toxin A) were similar in the two groups at 2 months, and the decline in antibody measured at 18 months was also similar. Because the two vaccines were safe and similarly immunogenic in the two vaccine groups, they can be administered simultaneously to patients or plasma donors in a practical vaccination schedule.

A case of rhinoscleroma cured with ciprofloxacin

The diagnosis of rhinoscleroma was confirmed in a 17-year-old female patient from Tehran, Iran, suffering from a roundish tumour of the nose. Prior treatment with streptomycin and tetracycline had been unsuccessful. A three-month course of high-dose oral ciprofloxacin (750 mg b.i.d.) led to prompt cessation of the growth of the granuloma which was removed later by plastic surgery. Although serology alone appeared to have little value for the specific diagnosis of rhinoscleroma, a significant increase of IgG antibodies during treatment with ciprofloxacin confirmed infection by Klebsiella rhinoscleromatis in this case.

Immunological cross-reactivity between Enterobacter aerogenes and Klebsiella capsular polysaccharides

Enterobacter aerogenes capsular polysaccharides (CPS) which cross-react with Klebsiella K3, K21, and K68 CPS were purified. Humans immunized with a vaccine containing Klebsiella K3 and K21 CPS produced antibody which recognized these E. aerogenes CPS. The magnitude of the immune response to the E. aerogenes CPS varied among the serotypes. Passive transfer of an immunoglobulin produced from the plasma of donors immunized with the above vaccine afforded significant protection against challenge with an E. aerogenes strain bearing a capsule which cross-reacts with Klebsiella K3 CPS.