Intranasal immunization with recombinant outer membrane protein P6 induces specific immune responses against nontypeable Haemophilus influenzae

Mucosal immunity of mannose-modified chitosan microspheres loaded with the nontyepable Haemophilus influenzae outer membrane protein P6 in BALB/c mice

Nontypeable Haemophilus influenzae (NTHi) is a common opportunistic pathogen that colonizes the nasopharynx. NTHi infections result in enormous global morbidity in two clinical settings: otitis media in children and acute exacerbation of chronic obstructive pulmonary disease (COPD) in adults. Thus, there is an urgent need to design and develop effective vaccines to prevent morbidity and reduce antibiotic use. The NTHi outer membrane protein P6, a potential vaccine candidate, is highly conserved and effectively induces protective immunity. Here, to enhance mucosal immune responses, P6-loaded mannose-modified chitosan (MC) microspheres (P6-MCMs) were developed for mucosal delivery. MC (18.75%) was synthesized by the reductive amination reaction method using sodium cyanoborohydride (NaBH₃CN), and P6-MCMs with an average size of 590.4±16.2 nm were successfully prepared via the tripolyphosphate (TPP) ionotropic gelation process. After intranasal immunization with P6-MCMs, evaluation of humoral immune responses indicated that P6-MCMs enhance both systemic and mucosal immune responses. Evaluation of cellular immune responses indicated that P6-MCMs enhance cellular immunity and trigger a mixed Th1/Th2-type immune response. Importantly, P6-MCMs also trigger a Th17-type immune response. They are effective in promoting lymphocyte proliferation and differentiation without toxicity in vitro. The results also demonstrate that P6-MCMs can effectively induce MHC class I- and II-restricted cross-presentation, promoting CD4⁺-mediated Th immune responses and CD8⁺-mediated cytotoxic T lymphocyte (CTL) immune responses. Evaluation of protective immunity indicated that immunization with P6-MCMs can reduce inflammation in the nasal mucosa and the lung and prevent NTHi infection. In conclusion, MCMs are a promising adjuvant-delivery system for vaccines against NTHi.

Pharyngeal Immunity in Early Vertebrates Provides Functional and Evolutionary Insight into Mucosal Homeostasis

The pharyngeal organ is located at the crossroad of the respiratory and digestive tracts in vertebrate, and it is continuously challenged by varying Ags during breathing and feeding. In mammals, the pharyngeal mucosa (PM) is a critical first line of defense. However, the evolutionary origins and ancient roles of immune defense and microbiota homeostasis of PM are still unknown. In this study, to our knowledge, we are the first to find that diffuse MALT is present in PM of rainbow trout, an early vertebrate. Importantly, following parasitic infection, we detect that strong parasite-specific mucosal IgT and dominant proliferation of IgT⁺ B cell immune responses occurs in trout PM, providing, to our knowledge, the first demonstration of local mucosal Ig responses against pathogens in pharyngeal organ of a nonmammal species. Moreover, we show that the trout PM microbiota is prevalently coated with secretory IgT and, to a much lesser degree, by IgM and IgD, suggesting the key role of mucosal Igs in the immune exclusion of teleost pharyngeal bacteria. Overall, to our knowledge, our findings provide the first evidence that pharyngeal mucosal immunity appear earlier than tetrapods.

The adhesins of non-typeable Haemophilus influenzae

INTRODUCTION

Nontypeable Haemophilus influenzae (NTHi) is an opportunistic pathogen of the respiratory tract and the greatest contributor to invasive Haemophilus disease. Additionally, in children, NTHi is responsible for the majority of otitis media (OM) which can lead to chronic infection and hearing loss. In adults, NTHi infection in the lungs is responsible for the onset of acute exacerbations in chronic obstructive pulmonary disease (COPD). Unfortunately, there is currently no vaccine available to protect against NTHi infections. Areas covered: NTHi uses an arsenal of adhesins to colonise the respiratory epithelium. The adhesins also have secondary roles that aid in the virulence of NTHi, including mechanisms that avoid immune clearance, adjust pore size to avoid antimicrobial destruction, form micro-colonies and invoke phase variation for protein mediation. Bacterial adhesins can also be ideal antigens for subunit vaccine design due to surface exposure and immunogenic capabilities. Expert commentary: The host-pathogen interactions of the NTHi adhesins are not fully investigated. The relationship between adhesins and the extracellular matrix (ECM) play a part in the success of NTHi colonisation and virulence by immune evasion, migration and biofilm development. Further research into these immunogenic proteins would further our understanding and enable a basis for better combatting NTHi disease.

Vaccines for Nontypeable Haemophilus influenzae: the Future Is Now

Infections due to nontypeable Haemophilus influenzae result in enormous global morbidity in two clinical settings: otitis media in children and respiratory tract infections in adults with chronic obstructive pulmonary disease (COPD). Recurrent otitis media affects up to 20% of children and results in hearing loss, delays in speech and language development and, in developing countries, chronic suppurative otitis media. Infections in people with COPD result in clinic and emergency room visits, hospital admissions, and respiratory failure. An effective vaccine would prevent morbidity, help control health care costs, and reduce antibiotic use, a major contributor to the global crisis in bacterial antibiotic resistance. The widespread use of the pneumococcal conjugate vaccines is causing a relative increase in H. influenzae otitis media. The partial protection against H. influenzae otitis media induced by the pneumococcal H. influenzae protein D conjugate vaccine represents a proof of principle of the feasibility of a vaccine for nontypeable H. influenzae. An ideal vaccine antigen should be conserved among strains, have abundant epitopes on the bacterial surface, be immunogenic, and induce protective immune responses. Several surface proteins of H. influenzae have been identified as potential vaccine candidates and are in various stages of development. With continued research, progress toward a broadly effective vaccine to prevent infections caused by nontypeable H. influenzae is expected over the next several years.

Bactericidal antibody response against P6, protein D, and OMP26 of nontypeable Haemophilus influenzae after acute otitis media in otitis-prone children

The bactericidal antibody response to three nontypeable Haemophilus influenzae (NTHi) outer membrane proteins (D, P6, and OMP26) was studied in 24 otitis-prone children (aged 7-28 months) after an acute otitis media (AOM) caused by NTHi. The study was carried out to understand the contribution of antigen-specific bactericidal antibody responses in the class of children who are most vulnerable to recurrent otitis media infections. Levels of protein D (P = 0.005) and P6 (P = 0.026) but not OMP26 antibodies were higher in bactericidal sera compared with nonbactericidal sera. For five (24%) and 16 (76%) of 21 bactericidal sera tested, removal of anti-protein D and P6 antibody, respectively, resulted in a two- to fourfold drop in bactericidal antibody. Antibodies to OMP26 did not make any contribution to the overall bactericidal activity in any serum samples. Eleven of 21 sera (52%) had bactericidal activity against a heterologous NTHi (86-028 NP) strain but the titers were significantly lower (P < 0.05) as compared to the homologous strains. Future studies of protein D, P6, OMP26, and other potential NTHi vaccine antigens should include studies of bactericidal antibody in children who are otitis prone as a possible correlate of protection.

Construction and immunogenicity of recombinant adenovirus vaccines expressing the HMW1, HMW2, or Hia adhesion protein of nontypeable Haemophilus influenzae

The objective of the present study was to construct and assess the immunogenicity of recombinant adenovirus vectors expressing the HMW1, HMW2, or Hia protein of nontypeable Haemophilus influenzae (NTHi). These proteins are critical adhesins and potential protective antigens expressed by NTHi. Segments of the hmw1A and hmw2A structural genes that encode the distal one-half of mature HMW1 or HMW2 were cloned into the T7 expression vector pGEMEX-2. These constructs encoded stable HMW1 or HMW2 recombinant fusion protein that expresses B-cell epitopes common to most NTHi strains. A segment of the hia gene that encodes the surface-exposed portion of mature Hia was also cloned into pGEMEX-2. The resulting T7 gene 10 translational fusions were excised from the parent plasmids and cloned into the shuttle plasmid pDC316. Cotransfection of HEK 293 cells with the pDC316 derivatives and pBHGloxΔE1,3Cre resulted in the production of viral plaques from which recombinant adenoviruses expressing fusion proteins were recovered. Chinchillas immunized intraperitoneally with a single 10(8)-PFU dose of either the HMW2 or Hia adenoviral construct developed high anti-HMW2 or anti-Hia serum antibody titers within 4 weeks of immunization. Chinchillas immunized intranasally with a single 10(7)- to 10(9)-PFU dose of the Hia adenoviral construct also developed high anti-Hia serum antibody titers within 8 weeks of immunization. Recombinant adenoviruses represent a promising system to induce mucosal and systemic immunity and protection against mucosal diseases such as otitis media. Recombinant adenoviruses expressing recombinant HMW1, HMW2, or Hia protein will be important new tools in NTHi vaccine development efforts.

Mouse models for human otitis media

Otitis media (OM) remains the most common childhood disease and its annual costs exceed $5 billion. Its potential for permanent hearing impairment also emphasizes the need to better understand and manage this disease. The pathogenesis of OM is multifactorial and includes infectious pathogens, anatomy, immunologic status, genetic predisposition, and environment. Recent progress in mouse model development is helping to elucidate the respective roles of these factors and to significantly contribute toward efforts of OM prevention and control. Genetic predisposition is recognized as an important factor in OM and increasing numbers of mouse models are helping to uncover the potential genetic bases for human OM. Furthermore, the completion of the mouse genome sequence has offered a powerful set of tools for investigating gene function and is generating a rich resource of mouse mutants for studying the genetic factors underlying OM.

Promiscuous peptides on the nontypeable Haemophilus influenzae P6 outer membrane protein

INTRODUCTION

P6 outer membrane protein is one of the candidates for a vaccine formulation against nontypeable Haemophilus influenzae (NTHi) infection. As otitis-prone children who have recurrent episodes of acute otitis media because of NTHi show an impaired immune response to P6, an innovative approach to vaccination is required to augment their immune response.

RESULTS AND DISCUSSION

We previously identified human HLA-DR9-restricted T cell epitope peptide and highly immunogenic analog peptides on P6 for peptide vaccine candidates. To develop a vaccine formulation effective in the general population, we identified promiscuous T cell epitope peptides (p41-55, p71-85) on P6. In addition to stimulating with potentially promiscuous peptides (p30-44, p45-59) selected using a computer algorithm, we established peptide-specific T cell lines which respond to P6.

CONCLUSION

Our present results indicate that these peptides would be candidates for a widely applicable peptide vaccine formulation.

Mouse models for the study of mucosal vaccination against otitis media

Otitis media (OM) is one of the most common infectious diseases in humans. The pathogenesis of OM involves nasopharyngeal (NP) colonization and retrograde ascension of the pathogen up the Eustachian tube into the middle ear (ME). Due to increasing rates of antibiotic resistance, there is an urgent need for vaccines to prevent infections caused by the most common causes of bacterial OM, including nontypeable Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis. Current vaccine strategies aim to diminish bacterial NP carriage, thereby reducing the likelihood of developing acute OM. To be effective, vaccination should induce local mucosal immunity both in the ME and in the NP. Studies in animal models have demonstrated that the intranasal route of vaccination is particularly effective at inducing immune responses in the nasal passage and ME for protection against OM. The mouse is increasingly used in these models, because of the availability of murine reagents and the existence of technology to manipulate murine models of disease immunologically and genetically. Previous studies confirmed the suitability of the mouse as a model for inflammatory processes in acute OM. Here, we discuss various murine models of OM and review the applicability of these models to assess the efficacy of mucosal vaccination and the mechanisms responsible for protection. In addition, we discuss various mucosal vaccine antigens, mucosal adjuvants and mucosal delivery systems.

Vaccine development for non-typeable Haemophilus influenzae and Moraxella catarrhalis: progress and challenges

An urgent need exists for vaccines to prevent infections caused by nontypeable Haemophilus influenzae and Moraxella catarrhalis. These bacteria cause otitis media in children, a clinical problem associated with enormous morbidity and cost. H. influenzae and M. catarrhalis also cause lower respiratory tract infections in adults with chronic lung disease. Infections in this clinical setting are associated with disability and death. Recent progress in identifying potential vaccine antigens in both bacteria raises great promise in developing effective vaccines. This paper reviews the key issues in vaccine development for H. influenzae and M. catarrhalis, including areas where progress has been stalled, and proposes areas that deserve investigation in the next 5 years.

Physico-chemical characterisation and immunogenicity of a multi-valent candidate vaccine against non-typeable Haemophilus influenzae and Moraxella catarrhalis

The physico-chemical characteristics and immunogenicity of a candidate vaccine against otitis media, prepared from recombinant lipidated outer membrane proteins (rLP4 and rLP6) from non-typeable Haemophilus influenzae (NTHi) and of the ubiquitous cell surface protein UspA2 from Moraxella catarrhalis, were evaluated. Optical spectroscopy, size exclusion chromatography and gel electrophoresis were used to characterise the purified protein components and assess their purity and molecular sizes. The results showed that the three proteins were highly purified. Possible dimers in rLP4, dimers and multimers in rLP6 and UspA2 were detected. Small amounts of rLP4 and rLP6 dimers and most of UspA2 complexes remained tightly bound even after SDS treatment under reducing conditions. Immunogenicity studies showed that all proteins induced substantial antibody responses in mice immunised with AlPO4-adsorbed rLP4, rLP6 or UspA2 or a combination of these proteins. However, combination of these proteins resulted in a reduced response to rLP4 and rLP6, but not to UspA2, suggesting interference between these proteins which should be taken into consideration during the development and evaluation of this vaccine.

Community-acquired pneumonia: paving the way towards new vaccination concepts

Despite the availability of antimicrobial agents and vaccines, community-acquired pneumonia remains a serious problem. Severe forms tend to occur in very young children and among the elderly, since their immune competence is eroded by immaturity and immune senescence, respectively. The main etiologic agents differ according to patient age and geographic area. Streptococcus pneumoniae, Haemophilus influenzae, respiratory syncytial virus (RSV) and parainfluenza virus type 3 (PIV-3) are the most important pathogens in children, whereas influenza viruses are the leading cause of fatal pneumonia in the elderly. Effective vaccines are available against some of these organisms. However, there are still many agents against which vaccines are not available or the existent ones are suboptimal. To tackle this problem, empiric approaches are now being systematically replaced by rational vaccine design. This is facilitated by the growing knowledge in the fields of immunology, microbial pathogenesis and host response to infection, as well as by the availability of sophisticated strategies for antigen selection, potent immune modulators and efficient antigen delivery systems. Thus, a new generation of vaccines with improved safety and efficacy profiles compared to old and new agents is emerging. In this chapter, an overview is provided about currently available and new vaccination concepts.

Mouse models as a tool to unravel the genetic basis for human otitis media

The pathogenesis of otitis media (OM) is multifactorial and includes infection, anatomical factors, immunologic status, genetic predisposition, and environmental factors. OM remains the most common cause of hearing impairment in childhood. Genetic predisposition is increasingly recognized as an important factor. The completion of the mouse genome sequence has offered a powerful basket of tools for investigating gene function and can expect to generate a rich resource of mouse mutants for the elucidation of genetic factors underlying OM. We review the literature and discuss recent progresses in developing mouse models and using mouse models to uncover the genetic basis for human OM.

Construction of a mutant and characterization of the role of the vaccine antigen P6 in outer membrane integrity of nontypeable Haemophilus influenzae

Outer membrane protein P6 is the subject of investigation as a vaccine antigen to prevent infections caused by nontypeable Haemophilus influenzae, which causes otitis media in children and respiratory tract infections in adults with chronic lung disease. P6 induces protective immune responses in animal models and is the target of potentially protective immune responses in humans. P6 is a 16-kDa lipoprotein that shares homology with the peptidoglycan-associated lipoproteins of gram-negative bacteria and is highly conserved among strains of H. influenzae. To characterize the function of P6, an isogenic mutant was constructed by replacing the P6 gene with a chloramphenicol resistance cassette. The P6 mutant showed altered colony morphology and slower growth in vitro than that of the parent strain. By electron microscopy, the P6 mutant cells demonstrated increased size, variability in size, vesicle formation, and fragility compared to the parent cells. The P6 mutant showed hypersensitivity to selected antibiotics with different mechanisms of action, indicating increased accessibility of the agents to their targets. The P6 mutant was more sensitive to complement-mediated killing by normal human serum. Complementation of the mutation in trans completely or partially restored the phenotypes. We concluded that P6 plays a structural role in maintaining the integrity of the outer membrane by anchoring the outer membrane to the cell wall. The observation that the absence of expression of P6 is detrimental to the cell is a highly desirable feature for a vaccine antigen, supporting further investigation of P6 as a vaccine candidate for H. influenzae.

Identification of human T-cell epitopes and highly immunogenic analog peptides on the non-typeable Haemophilus influenzae P6 outer membrane protein

P6 outer membrane protein is one of the candidates for a vaccine formulation against non-typeable Haemophilus influenzae (NTHi) infection. However, otitis-prone children who have recurrent episodes of acute otitis media due to NTHi fail to respond adequately to P6. An innovative approach to vaccination is therefore required to augment such children's immune response. To develop an effective peptide vaccine, we established P6-specific CD4(+) T-cell lines (TCLs) restricted by the human histocompatibility leukocyte antigen (HLA)-DR9 molecule, and revealed a human T-cell epitope on P6 and its core peptide sequence (p77-85; EYNIALGQR). Furthermore, we found that 3 analog peptides, E77D (the substitution of E at position 77 with D), N79G, and R85K, induced high proliferative responses as well as marked cytokine production when compared to the T-cell epitope peptide. These peptides may be candidates for a peptide vaccine formulation effective against NTHi infections, even in otitis-prone children.

Investigation of non-typeable Haemophilus influenzae outer membrane protein P6 as a new carrier for lipooligosaccharide conjugate vaccines

Non-typeable Haemophilus influenzae (NTHi) outer membrane protein P6 was used as a new protein carrier for NTHi detoxified lipooligosaccharide (dLOS) conjugates due to its conservation and potential to elicit bactericidal antibodies. P6 was covalently conjugated to dLOS of strain 9274 through adipic acid dihydrazide with different ratios of dLOS to P6, which resulted in two conjugate formulations with weight ratios of dLOS to P6 of 3.7 for dLOS-P6 (I) and 1.6 for dLOS-P6 (II). Binding activity of the conjugates was examined by an enzyme-linked immunosorbent assay with mouse monoclonal antibodies specific to LOS and P6 and a rabbit anti-P6 serum. The results showed that the conjugates bound not only to the LOS antibody but also to both P6 antibodies, suggesting that the conjugates retained epitopes of both LOS and P6 antigens. Animal studies revealed that dLOS-P6 (II) induced high levels of anti-LOS and anti-P6 IgGs in mice and rabbits. However, dLOS-P6 (I) induced lower levels of anti-LOS IgGs in mice and rabbits and anti-P6 IgGs in rabbits with no anti-P6 IgGs in mice. In addition, all rabbit, but not mouse, antisera elicited by the conjugates showed bactericidal activity against the homologous strain, and two of them elicited by each conjugate plus Ribi adjuvant showed cross-bactericidal activity against three of five major serotype stains. These data indicate that P6 could serve as an effective carrier for dLOS or other carbohydrate conjugates and that the ratio of carbohydrate to P6 might contribute to immune responses in vivo.

A recombinant P4 protein of Haemophilus influenzae induces specific immune responses biologically active against nasopharyngeal colonization in mice after intranasal immunization

Outer membrane protein P4, together with P6, is highly conserved among all typeable and nontypeable strains of Haemophilus influenzae (H. influenzae). Thus, the protein is an attractive antigen for the inclusion in a vaccine against nontypeable H. influenzae (NTHi). However, the ability of P4 to induce antibodies protective against NTHi infections is still controversial. In this study, we investigated the specific mucosal immune responses against NTHi induced by intranasal immunization with the lipidated form of recombinant P4 protein (rP4) and non-fatty acylated recombinant P6 protein (rP6) with or without cholera toxin (CT) in BALB/c mice model. Intranasal immunization with either rP4+CT, a mixture of rP4 and rP6+CT, or rP4 and rP6 without CT elicited anti-rP4 specific IgG antibody in serum of mice. Intranasal immunization with either rP4+CT or a mixture of rP4, rP6+CT elicited anti-rP4 specific IgA antibody in nasopharyngeal washing (NPW), while intranasal immunization with rP4 and rP6 without CT did not induced anti-rP4 specific IgA antibody responses in NPWs. Sera from mice intranasally immunized with rP4+CT and a mixture of rP4, rP6+CT also showed bactericidal activity. Significant clearance of NTHi in nasopharynx was seen 3 days after the inoculation of live NTHi in mice intranasally immunized with rP4+CT. The current findings suggested that P4 would be a useful antigen as the component of the vaccine to induce protective immune responses against NTHi. The use of an intranasal vaccine composed of the different surface protein antigens is an attractive strategy for the development of a vaccine against NTHi.

Respiratory infections caused by non-typeable Haemophilus influenzae

PURPOSE OF REVIEW

This review will consider recent developments in the clinical aspects of infections due to non-typeable Haemophilus influenzae. In addition, newer developments in the areas of mechanisms of pathogenesis, host pathogen interaction, immune responses and efforts toward vaccine development will be reviewed briefly.

RECENT FINDINGS

Non-typeable H. influenzae continues to be a common cause of otitis media in infants and children, sinusitis in children and adults, pneumonia in adults, and lower respiratory tract infection in adults with chronic obstructive pulmonary disease. While the rate of beta-lactamase production by isolates of H. influenzae varies geographically, most regions show a rate of 20-35% of isolates producing beta-lactamase. Recent studies have highlighted the possible role of bacterial biofilms formed by H. influenzae as a cause of otitis media. Several lines of evidence indicate that H. influenzae causes intracellular infection in the lower respiratory tract in chronic obstructive pulmonary disease and this observation has important implications in understanding the human immune response to the bacterium. Lipooligosaccharide is an important virulence factor for H. influenzae and research is generating new information on the complex role of this molecule in colonization and infection of the respiratory tract. Several surface molecules are under active evaluation as vaccine antigens.

SUMMARY

Non-typeable H. influenzae is an important cause of respiratory tract infections in children and adults. Most strains are susceptible to amoxicillin/clavulanate, fluoroquinolones and the newer macrolides. Research in the next decade promises substantial progress in the challenge of developing vaccines for nontypeable H. influenzae.

Chimeras of labile toxin one and cholera toxin retain mucosal adjuvanticity and direct Th cell subsets via their B subunit

Native cholera toxin (nCT) and the heat-labile toxin 1 (nLT) of enterotoxigenic Escherichia coli are AB5-type enterotoxins. Both nCT and nLT are effective adjuvants that promote mucosal and systemic immunity to protein Ags given by either oral or nasal routes. Previous studies have shown that nCT as mucosal adjuvant requires IL-4 and induces CD4-positive (CD4+) Th2-type responses, while nLT up-regulates Th1 cell production of IFN-gamma and IL-4-independent Th2-type responses. To address the relative importance of the A or B subunits in CD4+ Th cell subset responses, chimeras of CT-A/LT-B and LT-A/CT-B were constructed. Mice nasally immunized with CT-A/LT-B or LT-A/CT-B and the weak immunogen OVA developed OVA-specific, plasma IgG Abs titers similar to those induced by either nCT or nLT. Both CT-A/LT-B and LT-A/CT-B promoted secretory IgA anti-OVA Ab, which established their retention of mucosal adjuvant activity. The CT-A/LT-B chimera, like nLT, induced OVA-specific mucosal and peripheral CD4+ T cells secreting IFN-gamma and IL-4-independent Th2-type responses, with plasma IgG2a anti-OVA Abs. Further, LT-A/CT-B, like nCT, promoted plasma IgG1 more than IgG2a and IgE Abs with OVA-specific CD4+ Th2 cells secreting high levels of IL-4, but not IFN-gamma. The LT-A/CT-B chimera and nCT, but not the CT-A/LT-B chimera or nLT, suppressed IL-12R expression and IFN-gamma production by activated T cells. Our results show that the B subunits of enterotoxin adjuvants regulate IL-12R expression and subsequent Th cell subset responses.