Vaccine Candidates against Nontypeable Haemophilus influenzae: a Review

Phasevarions in Haemophilus influenzae biogroup aegyptius control expression of multiple proteins

IMPORTANCE

Haemophilus influenzae biogroup aegyptius is a human-adapted pathogen and the causative agent of Brazilian purpuric fever (BPF), an invasive disease with high mortality, that sporadically manifests in children previously suffering conjunctivitis. Phase variation is a rapid and reversible switching of gene expression found in many bacterial species, and typically associated with outer-membrane proteins. Phase variation of cytoplasmic DNA methyltransferases has been shown to play important roles in bacterial gene regulation and can act as epigenetic switches, regulating the expression of multiple genes as part of systems called phasevarions (phase-variable regulons). This study characterized two alleles of the ModA phasevarion present in H. influenzae biogroup aegyptius, ModA13, found in non-BPF causing strains and ModA16, unique to BPF causing isolates. Phase variation of ModA13 and ModA16 led to genome-wide changes to DNA methylation resulting in altered protein expression. These changes did not affect serum resistance in H. influenzae biogroup aegyptius strains.

In Vivo Validation of Novel Synthetic tbp1 Peptide-Based Vaccine Candidates against Haemophilus influenzae Strains in BALB/c Mice

Haemophilus influenzae is a Gram-negative bacterium characterized as a small, nonmotile, facultative anaerobic coccobacillus. It is a common cause of a variety of invasive and non-invasive infections. Among six serotypes (a-f), H. influenzae type b (Hib) is the most familiar and predominant mostly in children and immunocompromised individuals. Following Hib vaccination, infections due to other serotypes have increased in number, and currently, there is no suitable effective vaccine to induce cross-strain protective antibody responses. The current study was aimed to validate the capability of two 20-mer highly conserved synthetic tbp1 (transferrin-binding protein 1) peptide-based vaccine candidates (tbp1-E1 and tbp1-E2) predicted using in silico approaches to induce immune responses against H. influenzae strains. Cytokine induction ability, immune simulations, and molecular dynamics (MD) simulations were performed to confirm the candidacy of epitopic docked complexes. Synthetic peptide vaccine formulations in combination with two different adjuvants, BGs (Bacterial Ghosts) and CFA/IFA (complete/incomplete Freund's adjuvant), were used in BALB/c mouse groups in three booster shots at two-week intervals. An indirect ELISA was performed to determine endpoint antibody titers using the Student's t-distribution method. The results revealed that the synergistic use of both peptides in combination with BG adjuvants produced better results. Significant differences in absorbance values were observed in comparison to the rest of the peptide-adjuvant combinations. The findings of this study indicate that these tbp1 peptide-based vaccine candidates may present a preliminary set of peptides for the development of an effective cross-strain vaccine against H. influenzae in the future due to their highly conserved nature.

Improving Protection to Prevent Bacterial Infections: Preliminary Applications of Reverse Vaccinology against the Main Cystic Fibrosis Pathogens

Reverse vaccinology is a powerful tool that was recently used to develop vaccines starting from a pathogen genome. Some bacterial infections have the necessity to be prevented then treated. For example, individuals with chronic pulmonary diseases, such as Cystic Fibrosis, are prone to develop infections and biofilms in the thick mucus that covers their lungs, mainly caused by Burkholderia cepacia complex, Haemophilus influenzae, Mycobacterium abscessus complex, Pseudomonas aeruginosa and Staphylococcus aureus. These infections are complicated to treat and prevention remains the best strategy. Despite the availability of vaccines against some strains of those pathogens, it is necessary to improve the immunization of people with Cystic Fibrosis against all of them. An effective approach is to develop a broad-spectrum vaccine to utilize proteins that are well conserved across different species. In this context, reverse vaccinology, a method based on computational analysis of the genome of various microorganisms, appears as one of the most promising tools for the identification of putative targets for broad-spectrum vaccine development. This review provides an overview of the vaccines that are under development by reverse vaccinology against the aforementioned pathogens, as well as the progress made so far.

Multiplatform Metabolomics Characterization Reveals Novel Metabolites and Phospholipid Compositional Rules of Haemophilus influenzae Rd KW20

Haemophilus influenzae is a gram-negative bacterium of relevant clinical interest. H. influenzae Rd KW20 was the first organism to be sequenced and for which a genome-scale metabolic model (GEM) was developed. However, current H. influenzae GEMs are unable to capture several aspects of metabolome nature related to metabolite pools. To directly and comprehensively characterize the endometabolome of H. influenzae Rd KW20, we performed a multiplatform MS-based metabolomics approach combining LC-MS, GC-MS and CE-MS. We obtained direct evidence of 15-20% of the endometabolome present in current H. influenzae GEMs and showed that polar metabolite pools are interconnected through correlating metabolite islands. Notably, we obtained high-quality evidence of 18 metabolites not previously included in H. influenzae GEMs, including the antimicrobial metabolite cyclo(Leu-Pro). Additionally, we comprehensively characterized and evaluated the quantitative composition of the phospholipidome of H. influenzae, revealing that the fatty acyl chain composition is largely independent of the lipid class, as well as that the probability distribution of phospholipids is mostly related to the conditional probability distribution of individual acyl chains. This finding enabled us to provide a rationale for the observed phospholipid profiles and estimate the abundance of low-level species, permitting the expansion of the phospholipidome characterization through predictive probabilistic modelling.

Use of Inhaled Corticosteroids and Risk of Acquiring Haemophilus influenzae in Patients with Chronic Obstructive Pulmonary Disease

Background: Inhaled corticosteroids (ICS) are widely used in chronic obstructive pulmonary disease (COPD), despite the known risk of severe adverse effects including pulmonary infections. Research Question: Our study investigates the risk of acquiring a positive Haemophilus influenzae airway culture with use of ICS in outpatients with COPD. Study Design and Methods: We conducted an epidemiological cohort study using data from 1 January 2010 to 19 February 2018, including 21,218 outpatients with COPD in Denmark. ICS use 365 days prior to cohort entry was categorised into low, moderate, and high, based on cumulated ICS dose extracted from a national registry on reimbursed prescriptions. A Cox proportional hazards regression model was used to assess the future risk of acquiring H. Influenzae within 365 days from cohort entry, and sensitivity analyses were performed using propensity score matched models. Results: In total, 801 (3.8%) patients acquired H. Influenzae during follow-up. Use of ICS was associated with a dose-dependent increased risk of acquiring H. Influenzae with hazard ratio (HR) 1.2 (95% confidence interval (CI) 0.9−1.5, p value = 0.1) for low-dose ICS; HR 1.7 (95% CI 1.3−2.1, p value < 0.0001) for moderate dose; and HR 1.9 (95% CI 1.5−2.4, p value < 0.0001) for high-dose ICS compared to no ICS use. Results were confirmed in the propensity-matched model using the same categories. Conclusions: ICS use in outpatients with COPD was associated with a dose-dependent increase in risk of isolating H. Influenzae. This observation supports that high dose ICS should be used with caution.

Structural Characterization of Haemophilus influenzae Enolase and Its Interaction with Human Plasminogen by In Silico and In Vitro Assays

Haemophilus influenzae is the causal agent of invasive pediatric diseases, such as meningitis, epiglottitis, pneumonia, septic arthritis, pericarditis, cellulitis, and bacteremia (serotype b). Non-typeable H. influenzae (NTHi) strains are associated with localized infections, such as otitis media, conjunctivitis, sinusitis, bronchitis, and pneumonia, and can cause invasive diseases, such as as meningitis and sepsis in immunocompromised hosts. Enolase is a multifunctional protein and can act as a receptor for plasminogen, promoting its activation to plasmin, which leads to the degradation of components of the extracellular matrix, favoring host tissue invasion. In this study, using molecular docking, three important residues involved in plasminogen interaction through the plasminogen-binding motif (₂₅₁EFYNKENGMYE₂₆₂) were identified in non-typeable H. influenzae enolase (NTHiENO). Interaction with the human plasminogen kringle domains is conformationally stable due to the formation of four hydrogen bonds corresponding to enoTYR₂₅₃-plgGLU₁ (K2), enoTYR₂₅₃-plgGLY₃₁₀ (K3), and enoLYS₂₅₅-plgARG₄₇₁/enoGLU₂₅₁-plgLYS₄₆₈ (K5). On the other hand, in vitro assays, such as ELISA and far-western blot, showed that NTHiENO is a plasminogen-binding protein. The inhibition of this interaction using polyclonal anti-NTHiENO antibodies was significant. With these results, we can propose that NTHiENO–plasminogen interaction could be one of the mechanisms used by H. influenzae to adhere to and invade host cells.

The structure of nontypeable Haemophilus influenzae SapA in a closed conformation reveals a constricted ligand-binding cavity and a novel RNA binding motif

Nontypeable Haemophilus influenzae (NTHi) is a significant pathogen in respiratory disease and otitis media. Important for NTHi survival, colonization and persistence in vivo is the Sap (sensitivity to antimicrobial peptides) ABC transporter system. Current models propose a direct role for Sap in heme and antimicrobial peptide (AMP) transport. Here, the crystal structure of SapA, the periplasmic component of Sap, in a closed, ligand bound conformation, is presented. Phylogenetic and cavity volume analysis predicts that the small, hydrophobic SapA central ligand binding cavity is most likely occupied by a hydrophobic di- or tri- peptide. The cavity is of insufficient volume to accommodate heme or folded AMPs. Crystal structures of SapA have identified surface interactions with heme and dsRNA. Heme binds SapA weakly (Kd 282 μM) through a surface exposed histidine, while the dsRNA is coordinated via residues which constitute part of a conserved motif (estimated Kd 4.4 μM). The RNA affinity falls within the range observed for characterized RNA/protein complexes. Overall, we describe in molecular-detail the interactions of SapA with heme and dsRNA and propose a role for SapA in the transport of di- or tri-peptides.

Vaccinomics driven proteome-wide screening of Haemophilus influenzae for the prediction of common putative vaccine candidates

Haemophilus influenzae colonizes the respiratory tract and is associated with life-threatening invasive infections. The recent rise in its global prevalence, even in the presence of multiple vaccines, indicate an urgent need for developing cross-strain effective vaccine strategies. Our work focused on identifying the universally conserved antigenic regions of H. influenzae that can be used for developing new vaccines. A variety of bioinformatics tools were applied for the comprehensive geno-proteomic analysis of H. influenzae type "a" strain, as reference serotype, through which subcellular localization, essentiality, virulence, and non-host homology were determined. B and T-Cell epitope mapping of 3D protein structures were performed. Thereafter, molecular docking with HLA DRB1*0101 and comparative genome analysis established the candidature of identified regions. Based on the established vaccinomics criteria, five target proteins were predicted as novel vaccine candidates. Among these, 9 epitopic regions were identified that could regulate the lymphocyte activity through strong protein-protein interactions. Comparative genomic analysis exhibited that the identified regions were highly conserved among the different strains of H. influenzae. Based on multiple immunogenic factors, the five prioritized proteins and their predicted epitopes were identified as the ideal common putative vaccine candidate against typeable strains.

Panel 1: Biotechnology, biomedical engineering and new models of otitis media

OBJECTIVE

To summarize recently published key articles on the topics of biomedical engineering, biotechnology and new models in relation to otitis media (OM).

DATA SOURCES

Electronic databases: PubMed, Ovid Medline, Cochrane Library and Clinical Evidence (BMJ Publishing).

REVIEW METHODS

Articles on biomedical engineering, biotechnology, material science, mechanical and animal models in OM published between May 2015 and May 2019 were identified and subjected to review. A total of 132 articles were ultimately included.

RESULTS

New imaging technologies for the tympanic membrane (TM) and the middle ear cavity are being developed to assess TM thickness, identify biofilms and differentiate types of middle ear effusions. Artificial intelligence (AI) has been applied to train software programs to diagnose OM with a high degree of certainty. Genetically modified mice models for OM have further investigated what predisposes some individuals to OM and consequent hearing loss. New vaccine candidates protecting against major otopathogens are being explored and developed, especially combined vaccines, targeting more than one pathogen. Transcutaneous vaccination against non-typeable Haemophilus influenzae has been successfully tried in a chinchilla model. In terms of treatment, novel technologies for trans-tympanic drug delivery are entering the clinical domain. Various growth factors and grafting materials aimed at improving healing of TM perforations show promising results in animal models.

CONCLUSION

New technologies and AI applications to improve the diagnosis of OM have shown promise in pre-clinical models and are gradually entering the clinical domain. So are novel vaccines and drug delivery approaches that may allow local treatment of OM.

IMPLICATIONS FOR PRACTICE

New diagnostic methods, potential vaccine candidates and the novel trans-tympanic drug delivery show promising results, but are not yet adapted to clinical use.

Immunological characterisation of truncated lipooligosaccharide-outer membrane protein based conjugate vaccine against Moraxella catarrhalis and nontypeable Haemophilus influenzae

Moraxella catarrhalis and nontypeable Haemophilus influenzae are important bacterial causes of otitis media in children and respiratory diseases in adults. Lipooligosaccharide (LOS) from M. catarrhalis and outer membrane protein 26 (OMP26) from NTHi are major surface antigens identified as potential vaccine components against these organisms. We previously constructed M. catarrhalis in which LOS is truncated, but contains a structure common to the three known serotypes of M. catarrhalis. OMP26 is known to enhance clearance of NTHi following vaccination in animal models, so was chosen as the carrier protein. In this study, we conjugated wild-type and truncated M. catarrhalis detoxified-LOS to a recombinant modified OMP26, rOMP26VTAL. Vaccination of mice with these conjugates resulted in a significant increase in anti-LOS and anti-rOMP26VTAL IgG levels. Importantly, mouse antisera showed complement-mediated bactericidal activity against all M. catarrhalis serotype A and B strains and a NTHi strain tested. Serotypes A & B make up more than 90% of isolates. These data suggest that the LOS and OMP based conjugate can be used as vaccine components and require further investigation in animal models.

Phase-Variable Glycosylation in Nontypeable Haemophilus influenzae

Nontypeable Haemophilus influenzae (NTHi) is a leading cause of respiratory tract infections worldwide and continues to be a global health burden. Adhesion and colonization of host cells are crucial steps in bacterial pathogenesis, and in many strains of NTHi, the interaction with the host is mediated by the high molecular weight adhesins HMW1A and HMW2A. These adhesins are N-glycoproteins that are modified by cytoplasmic glycosyltransferases HMW1C and HMW2C. Phase variation in the number of short sequence repeats in the promoters of hmw1A and hmw2A directly affects their expression. Here, we report the presence of similar variable repeat elements in the promoters of hmw1C and hmw2C in diverse NTHi isolates. In an ex vivo assay, we systematically altered the substrate and glycosyltransferase expression and showed that both of these factors quantitatively affected the site-specific efficiency of glycosylation on HMW-A. This represents a novel mechanism through which phase variation can generate diversity in the quantitative extent of site-specific post-translational modifications on antigenic surface proteins. Glycosylation occupancy was incomplete at many sites, variable between sites, and generally lower close to the C-terminus of HMW-A. We investigated the causes of this variability. As HMW-C glycosylates HMW-A in the cytoplasm, we tested how secretion affected glycosylation on HMW-A and showed that retaining HMW-A in the cytoplasm indeed increased glycosylation occupancy across the full length of the protein. Site-directed mutagenesis showed that HMW-C had no inherent preference for glycosylating asparagines in NxS or NxT sequons. This work provides key insights into factors contributing to the heterogenous modifications of NTHi HMW-A adhesins, expands knowledge of NTHi population diversity and pathogenic capability, and is relevant to vaccine design for NTHi and related pathogens.

Intranasal coinfection model allows for assessment of protein vaccines against nontypeable Haemophilus influenzae in mice

PURPOSE

Nontypeable Haemophilus influenzae (NTHi) is a commensal in the human nasopharynx and the cause of pneumonia, meningitis, sinusitis, acute exacerbations of chronic obstructive pulmonary disease and acute otitis media (AOM). AOM is the most common ailment for which antibiotics are prescribed in the United States. With the emergence of new strains of antibiotic-resistant bacteria, finding an effective and broad coverage vaccine to protect against AOM-causing pathogens has become a priority. Mouse models are a cost-effective and efficient way to help determine vaccine efficacy. Here, we describe an NTHi AOM model in C57BL/6J mice, which also utilizes a mouse-adapted H1N1 influenza virus to mimic human coinfection.

METHODOLOGY

We tested our coinfection model using a protein vaccine formulation containing protein D, a well-studied NTHi vaccine candidate that can be found in the 10-valent Streptococcus pneumoniae conjugate vaccine. We verified the usefulness of our mouse model by comparing bacterial loads in the nose and ear between protein D-vaccinated and control mice.

RESULTS

While there was no measurable difference in nasal bacterial loads, we did detect significant differences in the bacterial loads of ear washes and ear bullae between vaccinated and control mice.

CONCLUSION

The results from this study suggest that our NTHi AOM coinfection model is useful for assessing protein vaccines.

Synthetic Glycans and Glycomimetics: A Promising Alternative to Natural Polysaccharides

A large quantity of polysaccharide-derived conjugate vaccines have been developed to combat various pathogenic infections. Another prominent polysaccharide, heparin, is listed as an essential drug by the World Health Organization (WHO) to treat thrombus. One of their common problems is that they all derive from natural polysaccharides. Specifically, capsular polysaccharides are mainly obtained from bacterial fermentation and unfractionated heparin is extracted from animal tissues such as porcine mucosa. The quality of natural polysaccharides is inconsistent and traces of contamination would cause a disaster. By contrast, the use of chemical or chemoenzymatic methods could provide structurally homogeneous and quality-controlled glycans. To date, large numbers of polysaccharide fragments and their analogues have been synthesized and evaluated. Some of them even showed comparable activities to their corresponding natural polysaccharides. Here, the latest advances in these synthetic glycan analogues ranging from carbohydrate-based vaccines, heparin-related therapeutics and glycomimetics of polysaccharides are summarized.

Haemophilus influenzae Pyomyositis in a Patient with Diabetic Ketoacidosis: A Unique Case and Review of Literature

Haemophilus influenzae is a Gram-negative bacillus commonly known to cause upper respiratory tract infections. Skin and soft tissue infections are very uncommon. Of these, the majority were associated with necrotizing fasciitis requiring emergent debridement. We report a case of pyomyositis caused by Haemophilus influenzae in an adult with diabetes.