Wild-type Outer Membrane Vesicles Research Articles

Preparation of bacterial outer membrane vesicles with anti-GPC3 single-chain antibody and identification of their targeting effects on hepatocellular carcinoma

This study aims to prepare bacterial outer membrane vesicles (OMVs) with anti-glypican-3 (GPC3) single-chain antibody and analyze their targeting effects on Hep G2 hepatocellular carcinoma (HCC) cells and tissue. The recombinant plasmid pET28a-Hbp-hGC 33-scFv was constructed by ligating Hbp-hGC 33-scFv to pET28a. Western blotting was employed to determine the prokaryotic expression of the fusion protein Hbp-hGC 33-scFv, on the basis of which the optimal induction conditions were determined. Hbp-hGC 33-OMVs secreted from the recombinant expressing strains were collected by ultrafiltration concentration and then characterized. The localization of Hbp-hGC 33-scFv in bacteria and Hbp-hGC 33-OMVs was analyzed by immune electron microscopy. The binding of Hbp-hGC 33-scFv to Hep G2 cells was observed by immunofluorescence. The Hep G2 tumor-bearing mouse model was established, and the targeted retention of Hbp-hGC 33-OMVs in the tumor site of mice was observed by a fluorescence imaging system in vivo. The results showed that the actual molecular weight of the fusion protein was 175.3 kDa, and the optimal induction conditions were as follows: OD600=0.5, IPTG added at a final concentration of 0.5 mmol/L, and overnight induction at 16 ℃. The prepared Hbp-hGC 33-OMVs were irregular spherical structures with an average particle size of (112.3±4.6) nm, expressing OmpC, OmpA, and the fusion protein Hbp-hGC 33-scFv. The Hbp-hGC 33-OMVs prepared in this study demonstrated stronger ability of binding to Hep G2 cells than the wild-type OMVs (P=0.008). All the data indicated that Hbp-hGC 33-OMVs with anti-GPC3 single-chain antibody were successfully prepared and could be used for research on the targeted therapy of hepatocellular carcinoma.

Recombinant outer membrane vesicles delivering eukaryotic expression plasmid of cytokines act as enhanced adjuvants against Helicobacter pylori infection in mice.

The widespread prevalence of Helicobacter pylori (H. pylori) infection remains a great challenge to human health. The existing vaccines are not ideal for preventing H. pylori infection; thus, exploring highly effective adjuvants may improve the immunoprotective efficacy of H. pylori vaccines. In a previous study, we found that the outer membrane vesicles (OMVs), a type of nanoscale particle spontaneously produced by Gram-negative bacteria, could act as adjuvants to boost the immune responses to vaccine antigens. In this study, we explored the potential application of OMVs as delivery vectors for adjuvant development. We constructed recombinant OMVs containing eukaryotic expression plasmid of cytokines, including interleukin 17A or interferon-γ, and evaluated their function as adjuvants in combination with inactivated whole-cell vaccine (WCV) or UreB as vaccine antigens. Our results showed that recombinant OMVs as adjuvants could induce stronger humoral and mucosal immune responses in mice than wild-type H. pylori OMVs and the cholera toxin (CT) adjuvant. Additionally, the recombinant OMVs significantly promoted Th1/Th2/Th17-type immune responses. Furthermore, the recombinant OMV adjuvant induced more potent clearance of H. pylori than CT and wild-type OMVs. Our findings suggest that the recombinant OMVs coupled with cytokines may become potent adjuvants for the development of novel and effective vaccines against H. pylori infection.

Disruption of sncRNA Improves the Protective Efficacy of Outer Membrane Vesicles against Helicobacter pylori Infection in a Mouse Model.

The outer membrane vesicles (OMVs) secreted by Helicobacter pylori contain various bacterial components, such as proteins, phospholipids, toxins, and nucleic acids, including small noncoding RNA (sncRNA), which have regulatory functions in cell envelope structure, metabolism, bacterial communication, biofilm formation, and virulence. We previously showed that knocking out sncRNAs sR-989262 and sR-2509025 at the cellular level increased interleukin 8 (IL-8) levels in mice exposed to OMVs. In this study, we show that immunization with ΔsR-989262 and ΔsR-2509025 OMVs intragastrically significantly increased immunoglobulin G (IgG) and secreted IgA levels in mice compared to wild-type OMVs and without weight changes, which indicated that sncRNA-deficient OMVs are relatively safe to immunize mice. The detection of IgG subtypes IgG1 and IgG2c showed that the sncRNA-deficient OMVs primarily stimulate the T helper 2 (Th2)-mediated immune response. Moreover, levels of the cytokines IL-4, IL-13, gamma interferon (IFN-γ), IL-12 (p40), IL-8, and IL-17 indicate that ΔsR-989262 and ΔsR-2509025 OMVs trigger the Th2-type immune response but primarily trigger a Th1-mediated and Th17-mediated immune response. These findings show that OMV-encapsulated sncRNA plays an important role in regulating the immune response in hosts infected by H. pylori at the animal level. Moreover, they show that knocking out of sR-989262 and sR-2509025 improves the immunogenicity and protective efficacy of OMVs, and this may be beneficial to the design of OMV-based H. pylori vaccines.

Inactivation of the Mla system and outer-membrane phospholipase A results in disrupted outer-membrane lipid asymmetry and hypervesiculation in Bordetella pertussis

Bordetella pertussis is the causative agent of a respiratory infection known as whooping cough. With the goal of improving the production of outer-membrane vesicles (OMVs), we studied here the mechanisms that are involved in maintaining lipid asymmetry in the outer membrane of this organism. We identified homologues of the phospholipid (PL)-transport systems Mla and Pqi and of outer-membrane phospholipase A (OMPLA). Inactivation of mlaF, encoding the ATPase of the Mla system, together with pldA, which encodes OMPLA, resulted in an accumulation of PLs at the cell surface as demonstrated by the binding of a phosphatidylethanolamine-specific fluorescent probe to intact cells of this strain. The corresponding single mutations did hardly or not affect binding of the probe. These results are consistent with a retrograde transport directionality of the Mla system in B. pertussis and indicate that PLs accumulating at the cell surface in the mlaF mutant are degraded by OMPLA. Consequently, the mlaF mutant showed a conditional growth defect due to the production of free fatty acids by OMPLA, which could be compensated by inactivation of OMPLA or by sequestration of the produced fatty acids with starch. The mlaF pldA double mutant showed markedly increased OMV production, and representative antigens were detected in these OMVs as in wild-type OMVs. Further phenotypic characterization showed that the barrier function of the outer membrane of the mlaF pldA mutant was compromised as manifested by increased susceptibility to SDS and to several antibiotics. Moreover, inactivation of mlaF alone or together with pldA resulted in increased biofilm formation, which was, however, not directly related to increased vesiculation as the addition of purified OMVs to the wild-type strain decreased biofilm formation. We conclude that the absence of MlaF together with OMPLA results in PL accumulation in the outer leaflet of the outer membrane, and the increased vesiculation of the mutant could be useful in the development of novel, OMV-based pertussis vaccines.

Surface Engineering of Escherichia coli–Derived OMVs as Promising Nano-Carriers to Target EGFR-Overexpressing Breast Cancer Cells

Bacterial outer membrane vesicles (OMVs) have recently drawn a great deal of attention due to their therapeutic efficiency and ability to target specific cells. In the present study, we sought to probe engineered OMVs as novel and promising carriers to target breast cancer cells. Following the fusion of the affiEGFR-GALA structure to the C-terminal of ClyA as an anchor protein, the ClyA-affiEGFR-GALA construct was successfully expressed on the surface of ∆msbB/∆pagP E. coli W3110-derived OMVs. Morphological features of the engineered and wild-type OMVs were identical. The engineered OMVs induced no endotoxicity, cytotoxicity, or immunogenicity, indicating the safety of their application. These OMVs could specifically bind to EGF receptors of MDA-MB-468 cells expressing high levels of EGFR and not to those with low levels of EGFR (HEK293T cells). Interestingly, despite a lower binding affinity of the engineered OMVs relative to the positive control Cetuximab, it was strong enough to identify these cells. Moreover, confocal microscopy revealed no uptake of the modified OMVs by the EGFR-overexpressing cells in the presence of EGFR competitors. These results suggest that OMVs might internalize into the cells with EGF receptors, as no OMVs entered the cells with any EGFR expression or those pretreated with EGF or Cetuximab. Regarding the EGFR-binding affinity of the engineered OMVs and their cellular uptake, they are presented here as a potential carrier for cell-specific drug delivery to treat a wide variety of cancer cells. Interestingly, the engineered OMVs are capable of reaching the cytoplasm while escaping the endosome due to the incorporation of a fusogenic GALA peptide in the construct.

Reciprocal Packaging of the Main Structural Proteins of Type 1 Fimbriae and Flagella in the Outer Membrane Vesicles of "Wild Type" Escherichia coli Strains.

Fundamental aspects of outer membrane vesicle (OMV) biogenesis and the engineering of producer strains have been major research foci for many in recent years. The focus of this study was OMV production in a variety of Escherichia coli strains including wild type (WT) (K12 and BW25113), mutants (from the Keio collection) and proprietary [BL21 and BL21 (DE3)] strains. The present study investigated the proteome and prospective mechanism that underpinned the key finding that the dominant protein present in E. coli K-12 WT OMVs was fimbrial protein monomer (FimA) (a polymerizable protein which is the key structural monomer from which Type 1 fimbriae are made). However, mutations in genes involved in fimbriae biosynthesis (ΔfimA, B, C, and F) resulted in the packaging of flagella protein monomer (FliC) (the major structural protein of flagella) into OMVs instead of FimA. Other mutations (ΔfimE, G, H, I, and ΔlrhA–a transcriptional regulator of fimbriation and flagella biosynthesis) lead to the packaging of both FimA and Flagellin into the OMVs. In the majority of instances shown within this research, the production of OMVs is considered in K-12 WT strains where structural appendages including fimbriae or flagella are temporally co-expressed throughout the growth curve as shown previously in the literature. The hypothesis, proposed and supported within the present paper, is that the vesicular packaging of the major FimA is reciprocally regulated with the major FliC in E. coli K-12 OMVs but this is abrogated in a range of mutated, non-WT E. coli strains. We also demonstrate, that a protein of interest (GFP) can be targeted to OMVs in an E. coli K-12 strain by protein fusion with FimA and that this causes normal packaging to be disrupted. The findings and underlying implications for host interactions and use in biotechnology are discussed.

Comparative transcriptomics between species attributes reactogenicity pathways induced by the capsular group B meningococcal vaccine, 4CMenB, to the membrane-bound endotoxin of its outer membrane vesicle component

The capsular group B meningococcal (MenB) four component vaccine (4CMenB) has been licensed for the prevention of invasive disease caused by MenB. The vaccine causes fever in infants, particularly when given in combination (concomitant) with other routinely-administered vaccines (routine), such as the standard diphtheria, tetanus, pertussis (DTP)-containing vaccine. To assess the suitability of a mouse immunisation model to study this phenomenon, we monitored temperature in mice after a second dose of routine vaccines, with or without 4CMenB, and compared the results with those in humans. Using this mouse model, we explored the reactogenicity of 4CMenB components by measuring changes in temperature, cytokines, and gene expression induced by 4CMenB, one of its components, wild-type or attenuated endotoxin outer membrane vesicles (OMVs), or lipopolysaccharide (LPS). A significant rise (p < 0.01) in temperature was observed in mice immunised with 4CMenB, wild-type OMVs, and LPS. RNA-sequencing of mouse whole blood revealed a gene signature shared by the 4CMenB, OMV, and LPS groups consisting of bacterial pattern recognition receptors and neutrophil activation marker genes. Sequencing of neutrophils isolated after concomitant 4CMenB identified cells expressing the OMV-associated genes Plek and Lcp1. Immunisation with 4CMenB or OMVs led to increased IL-6 in serum and significant upregulation (p < 0.0001) of prostaglandin-synthesising enzymes on brain tissue. These data demonstrate the suitability of a mouse model for assessing vaccine reactogenicity and strongly indicate that the fever following vaccination with 4CMenB in human infants is induced by endotoxin contained in the OMV component of the vaccine.

Sodium Taurocholate Stimulates Campylobacter jejuni Outer Membrane Vesicle Production via Down-Regulation of the Maintenance of Lipid Asymmetry Pathway.

Campylobacter jejuni outer membrane vesicles (OMVs) contain numerous virulence-associated proteins including the cytolethal distending toxin and three serine proteases. As C. jejuni lacks the classical virulence-associated secretion systems of other enteric pathogens that deliver effectors directly into target cells, OMVs may have a particularly important role in virulence. C. jejuni OMV production is stimulated by the presence of physiological concentrations of the bile salt sodium taurocholate (ST) through an unknown mechanism. The maintenance of lipid asymmetry (MLA) pathway has been implicated in a novel mechanism for OMV biogenesis, open to regulation by host signals. In this study we investigated the role of the MLA pathway in C. jejuni OMV biogenesis with ST as a potential regulator. OMV production was quantified by analyzing protein and lipid concentrations of OMV preparations and OMV particle counts produced by nanoparticle tracking analysis. Mutation of mlaA which encodes the outer membrane component of the MLA pathway significantly increased OMV production compared to the wild-type strain. Detergent sensitivity and membrane permeability assays confirmed the increased OMV production was not due to changes in membrane stability. The presence of 0.2% (w/v) ST increased wild-type OMV production and reduced OMV size, but did not further stimulate mlaA mutant OMV production or significantly alter mlaA mutant OMV size. qRT-PCR analysis demonstrated that the presence of ST decreased expression of both mlaA and mlaC in C. jejuni wild-type strains 11168 and 488. Collectively the data in this study suggests C. jejuni can regulate OMV production in response to host gut signals through changes in expression of the MLA pathway. As the gut bile composition is dependent on both diet and the microbiota, this study highlights the potential importance of diet and lifestyle factors on the varying disease presentations associated with gut pathogen infection.

Development of Bacteroides thetaiotaomicron outer membrane vesicles as a universal, mucosal vaccine for Influenza A virus

Influenza A Virus (IAV) is a zoonotic pathogen which causes seasonal epidemics worldwide, resulting in significant morbidity and mortality. Due to rapid virus evolution, available vaccines/antiviral drugs must be re-formulated and re-administered in most years. There is therefore an unmet need for a ‘universal’ vaccine to provide long-lasting, adaptive immunity to multiple strains of IAV. The aim of this study was to assess outer membrane vesicles (OMVs) produced by Bacteroides thetaiotaomicron (Bt) containing IAV antigens as a candidate universal mucosal vaccine. First, using intranasally-delivered fluorescently-labelled OMVs and FACS we demonstrated good uptake of OMVs by dendritic cells in both secondary and tertiary lymphoid tissue, showing OMVs are efficiently trafficked from the mucosa to the lymphatic system. Immunohistology confirmed this and showed expansion of lymphoid tissues and lymphoid follicles after OMV delivery. The stem/stalk of IAV HA is less variable and will generate antibodies that are cross-protective. Thus, we produced OMVs (termed H5F) that contained the stalk region of HA from strain A/VietNam/1203/04 (H5N1). We inoculated mice intranasally with H5F expressing OMVs or wild type OMVs and assessed antibody production and protection from challenge using a lethal dose of a different strain of influenza (PR8; H1N1). OMV-H5F-inoculted mice produced IgG and IgA in the respiratory tract that recognised both H5 HA and H1 HA. OMV-H5F inoculated mice were also protected from lethal challenge and supported lower virus titres. Our results indicate a strong potential for this approach to generate a universal IAV vaccine.

Analysis of Pseudomonas aeruginosa biofilm membrane vesicles supports multiple mechanisms of biogenesis.

Outer Membrane Vesicles (OMVs) are ubiquitous in bacterial environments and enable interactions within and between species. OMVs are observed in lab-grown and environmental biofilms, but our understanding of their function comes primarily from planktonic studies. Planktonic OMVs assist in toxin delivery, cell-cell communication, horizontal gene transfer, small RNA trafficking, and immune system evasion. Previous studies reported differences in size and proteomic cargo between planktonic and agar plate biofilm OMVs, suggesting possible differences in function between OMV types. In Pseudomonas aeruginosa interstitial biofilms, extracellular vesicles were reported to arise through cell lysis, in contrast to planktonic OMV biogenesis that involves the Pseudomonas Quinolone Signal (PQS) without appreciable autolysis. Differences in biogenesis mechanism could provide a rationale for observed differences in OMV characteristics between systems. Using nanoparticle tracking, we found that P. aeruginosa PAO1 planktonic and biofilm OMVs had similar characteristics. However, P. aeruginosa PA14 OMVs were smaller, with planktonic OMVs also being smaller than their biofilm counterparts. Large differences in Staphylococcus killing ability were measured between OMVs from different strains, and a smaller within-strain difference was recorded between PA14 planktonic and biofilm OMVs. Across all conditions, the predatory ability of OMVs negatively correlated with their size. To address biogenesis mechanism, we analyzed vesicles from wild type and pqsA mutant biofilms. This showed that PQS is required for physiological-scale production of biofilm OMVs, and time-course analysis confirmed that PQS production precedes OMV production as it does in planktonic cultures. However, a small sub-population of vesicles was detected in pqsA mutant biofilms whose size distribution more resembled sonicated cell debris than wild type OMVs. These results support the idea that, while a small and unique population of vesicles in P. aeruginosa biofilms may result from cell lysis, the PQS-induced mechanism is required to generate the majority of OMVs produced by wild type communities.

Engineered outer membrane vesicle is potent to elicit HPV16E7-specific cellular immunity in a mouse model of TC-1 graft tumor.

PurposeCurrently, therapeutic tumor vaccines under development generally lack significant effects in human clinical trials. Exploring a powerful antigen delivery system is a potential approach to improve vaccine efficacy. We sought to explore engineered bacterial outer membrane vesicles (OMVs) as a new vaccine carrier for efficiently delivering tumor antigens and provoking robust antitumor immune responses.Materials and methodsFirst, the tumoral antigen human papillomavirus type 16 early protein E7 (HPV16E7) was presented on Escherichia coli-derived OMVs by genetic engineering methods, acquiring the recombinant OMV vaccine. Second, the ability of recombinant OMVs delivering their components and the model antigen green fluorescent protein to antigen-presenting cells was investigated in the macrophage Raw264.7 cells and in bone marrow-derived dendritic cells in vitro. Third, it was evaluated in TC-1 graft tumor model in mice that the recombinant OMVs displaying HPV16E7 stimulated specific cellular immune response and intervened the growth of established tumor.ResultsE. coli DH5α-derived OMVs could be taken up rapidly by dendritic cells, for which vesicle structure has been proven to be important. OMVs significantly stimulated the expression of dendritic cellmaturation markers CD80, CD86, CD83 and CD40. The HPV16E7 was successfully embedded in engineered OMVs through gene recombinant techniques. Subcutaneous immunization with the engineered OMVs induced E7 antigen-specific cellular immune responses, as shown by the increased numbers of interferon-gamma-expressing splenocytes by enzyme-linked immunospot assay and interferon-gamma-expressing CD4+ and CD8+ cells by flow cytometry analyses. Furthermore, the growth of grafted TC-1 tumors in mice was significantly suppressed by therapeutic vaccination. The recombinant E7 proteins presented by OMVs were more potent than those mixed with wild-type OMVs or administered alone for inducing specific cellular immunity and suppressing tumor growth.ConclusionThe results indicated that the nano-grade OMVs might be a useful vaccine platform for antigen delivery in cancer immunotherapy.

Outer membrane vesicles derived from Salmonella Typhimurium mutants with truncated LPS induce cross-protective immune responses against infection of Salmonella enterica serovars in the mouse model

Salmonella enterica cause diarrheal and systemic diseases and are of considerable concern worldwide. Vaccines that are cross-protective against multiple serovars could provide effective control of Salmonella-mediated diseases. Bacteria-derived outer membrane vesicles (OMVs) are highly immunogenic and are capable of eliciting protective immune responses. Alterations in lipopolysaccharide (LPS) length can result in outer membrane remodeling and composition of outer membrane proteins (OMPs) changing. In this study, we investigated the impact of truncated LPS on both the production and immunogenicity of Salmonella OMVs, including the ability of OMVs to elicit cross-protection against challenge by heterologous Salmonella strains. We found that mutations in waaJ and rfbP enhanced vesiculation, while mutations in waaC, waaF and waaG inhibited this process. Animal experiments indicated that OMVs from waaC, rfaH and rfbP mutants induced stronger serum immune responses compared to OMVs from the parent strain, while all elicited protective responses against the wild-type S. Typhimurium challenge. Furthermore, intranasal or intraperitoneal immunization with OMVs derived from the waaC and rfbP mutants elicited significantly higher cross-reactive IgG responses and provided enhanced cross-protection against S. Choleraesuis and S. Enteritidis challenge than the wild-type OMVs. These results indicate that truncated-LPS OMVs are capable of conferring cross protection against multiple serotypes of Salmonella infection.

Increased Outer Membrane Vesicle Formation in a Helicobacter pylori tolB Mutant.

Multiple studies have established the importance of the tol-pal gene cluster in bacterial cell membrane integrity and outer membrane vesicle (OMV) formation in Escherichia coli. In contrast, the functions of Tol-Pal proteins in pathogenic organisms, including those of the Epsilonproteobacteria, remain poorly if at all defined. The aim of this study was to characterize the roles of two key components of the Tol-Pal system, TolB and Pal, in OMV formation in the pathogenic bacterium, Helicobacter pylori. H. pylori ΔtolB, Δpal and ΔtolBpal mutants, as well as complemented strains, were generated and assessed for changes in morphology and OMV production by scanning electron microscopy and enzyme-linked immunoassay (ELISA), respectively. The protein content and pro-inflammatory properties of OMVs were determined by mass spectroscopy and interleukin-8 (IL-8) ELISA on culture supernatants from OMV-stimulated cells, respectively. H. pylori ΔtolB and Δpal bacteria exhibited aberrant cell morphology and/or flagella biosynthesis. Importantly, the disruption of H. pylori tolB but not pal resulted in a significant increase in OMV production. The OMVs from H. pylori ΔtolB and Δpal bacteria harbored many of the major outer membrane and virulence proteins observed in wild-type (WT) OMVs. Interestingly, ΔtolB, Δpal and ΔtolBpal OMVs induced significantly higher levels of IL-8 production by host cells, compared with WT OMVs. This work demonstrates that TolB and Pal are important for membrane integrity in H. pylori. Moreover, it shows how H. pylori tolB-pal genes may be manipulated to develop "hypervesiculating" strains for vaccine purposes.

Campylobacter jejuni Outer Membrane Vesicles Play an Important Role in Bacterial Interactions with Human Intestinal Epithelial Cells

Campylobacter jejuni is the most prevalent cause of food-borne gastroenteritis in the developed world; however, the molecular basis of pathogenesis is unclear. Secretion of virulence factors is a key mechanism by which enteric bacterial pathogens interact with host cells to enhance survival and/or damage the host. However, C. jejuni lacks the virulence-associated secretion systems possessed by other enteric pathogens. Many bacterial pathogens utilize outer membrane vesicles (OMVs) for delivery of virulence factors into host cells. In the absence of prototypical virulence-associated secretion systems, OMVs could be an important alternative for the coordinated delivery of C. jejuni proteins into host cells. Proteomic analysis of C. jejuni 11168H OMVs identified 151 proteins, including periplasmic and outer membrane-associated proteins, but also many determinants known to be important in survival and pathogenesis, including the cytolethal distending toxin (CDT). C. jejuni OMVs contained 16 N-linked glycoproteins, indicating a delivery mechanism by which these periplasm-located yet immunogenic glycoproteins can interact with host cells. C. jejuni OMVs possess cytotoxic activity and induce a host immune response from T84 intestinal epithelial cells (IECs), which was not reduced by OMV pretreatment with proteinase K or polymyxin B prior to coincubation with IECs. Pretreatment of IECs with methyl-beta-cyclodextrin partially blocks OMV-induced host immune responses, indicating a role for lipid rafts in host cell plasma membranes during interactions with C. jejuni OMVs. OMVs isolated from a C. jejuni 11168H cdtA mutant induced interleukin-8 (IL-8) to the same extent as did wild-type OMVs, suggesting OMV induction of IL-8 is independent of CDT.

Outer membrane vesicles obtained from Bordetella pertussis Tohama expressing the lipid A deacylase PagL as a novel acellular vaccine candidate

In an effort to devise a safer and effective pertussis acelullar vaccine, outer membrane vesicles (OMVs) were engineered to decrease their endotoxicity. The pagL gene from Bordetella bronchiseptica, which encodes a lipid A 3-deacylase, was expressed in Bordetella pertussis strain Tohama I. The resulting OMVs, designated OMVsBpPagL, contain tetra- instead of penta-acylated LOS, in addition to pertussis surface immunogens such as pertactin and pertussis toxin, as the wild type OMVs. The characterized pertussis OMVsBpPagL were used in murine B. pertussis intranasal (i.n.) challenge model to examine their protective capacity when delivered by i.n. routes. Immunized BALB/c mice were challenged with sublethal doses of B. pertussis. Significant differences between immunized animals and the PBS treated group were observed (p<0.001). Adequate elimination rates (p<0.005) were observed in mice immunized either with OMVsBpPagL and wild type OMVs. All OMV preparations tested were non toxic according to WHO criteria; however, OMVsBpPagL displayed almost no weight loss at 3 days post administration, indicating less toxicity when compared with wild type OMVs. Induction of IL6- and IL1-expression in lung after i.n. delivery as well as neutrophil recruitment to airways showed coincident results, with a lower induction of the proinflammatory cytokines and lower recruitment in the case of OMVsBpPagL compared to wild type OMVs.Given their lower endotoxic activity and retained protective capacity in the mouse model, OMVsBpPagL obtained from B. pertussis seem as interesting candidates to be considered for the development of novel multi-antigen vaccine.

Epidemiology of pathogenic Neisseria meningitidis serogroup B serosubtypes in Malta: Implications for introducing PorA based vaccines

Objective To describe the epidemiology of the serosubtypes of Neisseria meningitidis serogroup B (MenB) in the most densely populated area in Europe and to review the MenB Porin A (PorA) based outer membrane vesicle (OMV) vaccines that could provide the broadest protection. Study design and setting Active surveillance of invasive meningococcal disease in a population of 400,000 inhabitants in Malta from 1999 to 2006. Serogroup B isolates were serosubtyped and analysed by age and year. The suitability of OMV vaccines was then assessed. Results Laboratory confirmation of invasive meningococcal disease was obtained in 48% (79/163) of notified cases. Serogroup B caused the majority of invasive meningococcal disease (76%, 60/79) with the greatest disease burden occurring in 0–14-year-old children (73%, 44/60). MenC caused 14% (11/79) of cases. The most prevalent MenB serotype:serosubtype combination was B:4:P1.19,15 which constituted 59% (34/58) of all phenotypeable MenB isolates. The PorA epitopes P1.15 and P1.19, detected in 74% (43/58) of isolates, were significantly more prevalent than serosubtypes with other PorA epitopes ( χ 2: 7.18, P < 0.01). Conclusion An assessment of the usefulness of a MenB OMV vaccine in Malta requires further research. The wild-type OMV vaccine developed by the Finlay Institute (FI) in Cuba could potentially be used to control an outbreak with a MenB P1.19,15 clone. A multivalent OMV vaccine would however be needed for broader protection against the endemic heterogenous MenB strains. A serogroup B vaccine incorporating more conserved proteins than PorA would be more suitable for comprehensive control of meningococcal B disease.

Bactericidal Antibody Responses Elicited by a Meningococcal Outer Membrane Vesicle Vaccine with Overexpressed Factor H–Binding Protein and Genetically Attenuated Endotoxin

Outer membrane vesicle (OMV) vaccines from mutant Neisseria meningitidis strains engineered to overexpress factor H-binding protein (fHbp) have elicited broadly protective serum antibody responses in mice. The vaccines investigated were not treated with detergents to avoid extracting fHbp, which is a lipoprotein. Because of their high endotoxin content, the vaccines would not be safe to administer to humans. We prepared a native OMV vaccine from a strain engineered to overexpress fHbp and in which the gene encoding LpxL1 was inactivated, which reportedly decreases endotoxin activity. The OMV vaccine from the mutant had a similar or lower ability to induce the expression of proinflammatory cytokines by human peripheral blood mononuclear cells, compared with a detergent-extracted wild-type OMV, and 1000-10,000-fold lower activity than a native wild-type OMV. In mice, the OMV vaccine from the mutant elicited higher serum bactericidal antibody responses to a panel of heterologous N. meningitidis strains than did a control multicomponent recombinant protein vaccine or a detergent-extracted OMV vaccine that has been demonstrated to confer protection against meningococcal disease in humans. The data illustrate the potential to develop a broadly immunogenic native OMV vaccine that has decreased endotoxin activity and is potentially suitable for testing in humans.

Immunogenicity studies with a genetically engineered hexavalent PorA and a wild-type meningococcal group B outer membrane vesicle vaccine in infant cynomolgus monkeys

The immunogenicity of two meningococcal outer membrane vesicle (OMV) vaccines, namely the Norwegian wild-type OMV vaccine and the Dutch hexavalent PorA OMV vaccine, were examined in infant cynomolgus monkeys. For the first time, a wild-type- and a recombinant OMV vaccine were compared. Furthermore, the induction of memory and the persistence of circulating antibodies were measured. The Norwegian vaccine contained all four classes of major outer membrane proteins (OMP) and wild-type L3/L8 lipopolysaccharide (LPS). The Dutch vaccine consisted for 90% of class 1 OMPs, had low expression of class 4 and 5 OMP, and GalE LPS. Three infant monkeys were immunised with a human dose at the age of 1.5, 2.5 and 4.5 months. Two monkeys of each group received a fourth dose at the age of 11 months. In ELISA, both OMV vaccines were immunogenic and induced booster responses, particularly after the fourth immunisation. The Norwegian vaccine mostly induced sero-subtype P1.7,16 specific serum bactericidal antibodies (SBA), although some other SBA were induced as well. The antibody responses against P1.7,16, induced by the Norwegian vaccine, were generally higher than for the Dutch vaccine. However, the Dutch vaccine induced PorA specific SBA against all six sero-subtypes included in the vaccine showing differences in the magnitude of SBA responses to the various PorAs.