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

Evaluation of a protective effect of in ovo delivered Campylobacter jejuni OMVs

Campylobacter jejuni is the most prevalent cause of a food-borne gastroenteritis in the developed world, with poultry being the main source of infection. Campylobacter jejuni, like other Gram-negative bacteria, constitutively releases outer membrane vesicles (OMVs). OMVs are highly immunogenic, can be taken up by mammalian cells, and are easily modifiable by recombinant engineering. We have tested their usefulness for an oral (in ovo) vaccination of chickens. Four groups of 18-day-old chicken embryos (164 animals) underwent injection of wt C. jejuni OMVs or modified OMVs or PBS into the amniotic fluid. The OMVs modifications relied on overexpression of either a complete wt cjaA gene or the C20A mutant that relocates to the periplasm. Fourteen days post-hatch chicks were orally challenged with live C. jejuni strain. Cecum colonization parameters were analyzed by two-way ANOVA with Tukey post-hoc test. The wtOMVs and OMVs with wtCjaA overexpression were found to confer significant protection of chicken against C. jejuni (p = 0.03 and p = 0.013, respectively) in comparison to PBS controls and are promising candidates for further in ovo vaccine development.

The Power of Asymmetry: Architecture and Assembly of the Gram-Negative Outer Membrane Lipid Bilayer

Determining the chemical composition of biological materials is paramount to the study of natural phenomena. Here, we describe the composition of model gram-negative outer membranes, focusing on the predominant assembly, an asymmetrical bilayer of lipid molecules. We also give an overview of lipid biosynthetic pathways and molecular mechanisms that organize this material into the outer membrane bilayer. An emphasis is placed on the potential of these pathways as targets for antibiotic development. We discuss deviations in composition, through bacterial cell surface remodeling, and alternative modalities to the asymmetric lipid bilayer. Outer membrane lipid alterations of current microbiological interest, such as lipid structures found in commensal bacteria, are emphasized. Additionally, outer membrane components could potentially be engineered to develop vaccine platforms. Observations related to composition and assembly of gram-negative outer membranes will continue to generate novel discoveries, broaden biotechnologies, and reveal profound mysteries to compel future research.

Characterization of the immune response induced by pertussis OMVs-based vaccine

For the development of a third generation of pertussis vaccine that could improve the control of the disease, it was proposed that the immune responses induced by the classic whole cell vaccine (wP) or after infection should be used as a reference point. We have recently identified a vaccine candidate based on outer membrane vesicles (OMVs) derived from the disease etiologic agent that have been shown to be safe and protective in mice model of infection. Here we characterized OMVs-mediated immunity and the safety of our new candidate. We also deepen the knowledge of the induced humoral response contribution in pertussis protection. Regarding the safety of the OMVs based vaccine (TdapOMVsBp,) the in vitro whole blood human assay here performed, showed that the low toxicity of OMVs-based vaccine previously detected in mice could be extended to human samples. Stimulation of splenocytes from immunized mice evidenced the presence of IFN-γ and IL-17-producing cells, indicated that OMVs induces both Th1 and Th17 response. Interestingly TdapOMVsBp-raised antibodies such as those induced by wP and commercial acellular vaccines (aP) which contribute to induce protection against Bordetella pertussis infection. As occurs with wP-induced antibodies, the TdapOMVsBp-induced serum antibodies efficiently opsonized B. pertussis. All the data here obtained shows that OMVs based vaccine is able to induce Th1/Th17 and Th2 mixed profile with robust humoral response involved in protection, positioning this candidate among the different possibilities to constitute the third generation of anti-pertussis vaccines.

Myxobacterial vesicles death at a distance?

Outer membrane vesicles (OMVs) are produced from the outer membrane (OM) of myxobacterial cells and are found in large quantities within myxobacterial biofilms. It has been proposed that OMVs are involved in several of the social behaviors exhibited by the myxobacteria, including motility and predation. Proteomic data suggest that specific proteins are either selectively incorporated into or excluded from myxobacterial OMVs, as observed for OMVs of other organisms. Hydrolases are found in large numbers in OMVs, which then transport them to target bacteria. Fusion of OMVs with the OM of Gram-negative cells, or lysis of OMVs next to Gram-positive bacteria, is thought to deliver hydrolases to target cells, causing their lysis. The model myxobacterium Myxococcus xanthus is a predator of other bacteria, and OMVs are likely employed as predatory agents by this organism. The transfer of motility proteins between cells of M. xanthus has been documented, and OMV-mediated transfer provides a convenient mechanism to explain this phenomenon. This review describes the general principles of OMV biology, provides an overview of myxobacterial behavior, summarizes what is currently known about myxobacterial OMVs, and discusses the potential involvement of OMVs in many features of the myxobacterial life-cycle.

Glycoengineered Outer Membrane Vesicles: A Novel Platform for Bacterial Vaccines

The World Health Organization has indicated that we are entering into a post-antibiotic era in which infections that were routinely and successfully treated with antibiotics can now be lethal due to the global dissemination of multidrug resistant strains. Conjugate vaccines are an effective way to create a long-lasting immune response against bacteria. However, these vaccines present many drawbacks such as slow development, high price, and batch-to-batch inconsistencies. Alternate approaches for vaccine development are urgently needed. Here we present a new vaccine consisting of glycoengineered outer membrane vesicles (geOMVs). This platform exploits the fact that the initial steps in the biosynthesis of most bacterial glycans are similar. Therefore, it is possible to easily engineer non-pathogenic Escherichia coli lab strains to produce geOMVs displaying the glycan of the pathogen of interest. In this work we demonstrate the versatility of this platform by showing the efficacy of geOMVs as vaccines against Streptococcus pneumoniae in mice, and against Campylobacter jejuni in chicken. This cost-effective platform could be employed to generate vaccines to prevent infections caused by a wide variety of microbial agents in human and animals.

Outer membrane vesicles as platform vaccine technology

Outer membrane vesicles (OMVs) are released spontaneously during growth by many Gram-negative bacteria. They present a range of surface antigens in a native conformation and have natural properties like immunogenicity, self-adjuvation and uptake by immune cells which make them attractive for application as vaccines against pathogenic bacteria. In particular with Neisseria meningitidis, they have been investigated extensively and an OMV-containing meningococcal vaccine has recently been approved by regulatory agencies. Genetic engineering of the OMV-producing bacteria can be used to improve and expand their usefulness as vaccines. Recent work on meningitis B vaccines shows that OMVs can be modified, such as for lipopolysaccharide reactogenicity, to yield an OMV product that is safe and effective. The overexpression of crucial antigens or simultaneous expression of multiple antigenic variants as well as the expression of heterologous antigens enable expansion of their range of applications. In addition, modifications may increase the yield of OMV production and can be combined with specific production processes to obtain high amounts of well-defined, stable and uniform OMV particle vaccine products. Further improvement can facilitate the development of OMVs as platform vaccine product for multiple applications.

Strategies and new developments to control pertussis, an actual health problem

The aim of this article is to describe the current epidemiological situation of pertussis, as well as different short-term strategies that have been implemented to alleviate this threat. The state of the art of the development of new vaccines that are expected to provide long-lasting immunity against pertussis was also included.

Development of improved pertussis vaccine

Rates of infection with Bordetella pertussis, the gram-negative bacterium that causes the respiratory disease called whooping cough or pertussis, have not abated and 16 million cases with almost 200,000 deaths are estimated by the WHO to have occurred worldwide in 2008. Despite relatively high vaccination rates, the disease has come back in recent years to afflict people in numbers not seen since the pre-vaccine days. Indeed, pertussis is now recognized as a frequent infection not only in newborn and infants but also in adults. The disease symptoms also can be induced by the non-vaccine-preventable infection with the close species B. parapertussis for which an increasing number of cases have been reported. The epidemiologic situation and current knowledge of the limitations of pertussis vaccine point out the need to design improved vaccines. Several alternative approaches and their challenges are summarized.

Altered host immune responses to membrane vesicles from Salmonella and Gram-negative pathogens

Membrane vesicles (MVs), discrete nano-structures produced from the outer membrane of Gram-negative bacteria such as Salmonella enterica Typhimurium (S. Typhimurium), strongly activate dendritic cells (DCs), contain major antigens (Ags) recognized by Salmonella-specific B-cells and CD4+ T-cells, and provide protection against S. Typhimurium challenge in a mouse model. With this in mind, we hypothesized that alterations to the gene expression profile of bacteria will be reflected in the immunologic response to MVs. To test this, we assessed the ability of MVs from wild-type (WT) S. Typhimurium or a strain with a phenotype mimicking the intracellular-phase of S. Typhimurium (PhoP(c)) to activate dendritic cells and initiate a strong inflammatory response. MVs, isolated from wild-type and PhoP(c)S. Typhimurium (WTMVs and PhoPcMVs, respectively) had pro-inflammatory properties consistent with the parental bacterial strains: PhoPcMVs were less stimulatory for DC activation in vitro and were impaired for subsequent inflammatory responses compared to WTMVs. Interestingly, the reduced pro-inflammatory properties of PhoPcMVs did not completely rely on signals through TLR4, the receptor for LPS. Nonetheless, both WTMVs and PhoPcMVs contained abundant immunogenic antigens capable of being recognized by memory-immune CD4+ T-cells from mice previously infected with S. Typhimurium. Furthermore, we analyzed a suite of pathogenic Gram-negative bacteria and their purified MVs for their ability to activate DCs and stimulate inflammation in a manner consistent with the known inflammatory properties of the parental strains, as shown for S. Typhimurium. Finally, analysis of the potential vaccine utility of S. Typhimurium MVs revealed their capacity to encapsulate an exogenous model antigen and stimulate antigen-specific CD4+ and CD8+ T-cell responses. Taken together, our results demonstrate the dependence of bacterial cell gene expression for MV immunogenicity and subsequent in vitro immunologic response, as well as their potential utility as a vaccine platform.

Biosynthetically engineered lipopolysaccharide as vaccine adjuvant

Lipopolysaccharide (LPS), a dominant component of the Gram-negative bacterial outer membrane, is a strong activator of the innate immune system, and thereby an important determinant in the adaptive immune response following bacterial infection. This adjuvant activity can be harnessed following immunization with bacteria-derived vaccines that naturally contain LPS, and when LPS or molecules derived from it are added to purified vaccine antigens. However, the downside of the strong biological activity of LPS is its ability to contribute to vaccine reactogenicity. Modification of the LPS structure allows triggering of a proper immune response needed in a vaccine against a particular pathogen while at the same time lowering its toxicity. Extensive modifications to the basic structure are possible by using our current knowledge of bacterial genes involved in LPS biosynthesis and modification. This review focuses on biosynthetic engineering of the structure of LPS and implications of these modifications for generation of safe adjuvants.

Heterologous Expression of 3-O-Deacylase in Modulates the Endotoxicity of Lipopolysaccharide

The lipopolysaccharide (LPS) of <i>Acinetobacter baumannii</i> is a potent stimulator of proinflammatory cytokines, such as interleukin-6 (IL-6). The 3-O-deacylase (PagL)-modifying enzyme that removes the 3-O-linked acyl chain from the disaccharide backbone of lipid A provides the opportunity to develop a new therapeutic compound that could reduce detrimental inflammatory responses. The plasmid pMMB66EH-PagL obtained by recombinant DNA technology was electroporated into <i>A. baumannii</i> ATCC 19606. Compared with wild-type LPS, outer membrane vesicles and inactivated whole cells of engineered bacteria had a statistically significant decreased ability to produce IL-6. Structural analysis of lipid A by negative-ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed that the profile of lipid A fractions under PagL expression was changed. Taken together, our data showed that recombinant penta-acylated lipid A had less immunoreactivity and that the tetra-acylated version of lipid A with TLR4 antagonist activity decreased the induction of IL-6 production in the murine macrophage cell line J774 A.1.

Structure characterization of phospholipids and lipid A of Pseudomonas putida KT2442

Pseudomonas putida KT2442 is an important bacterium for producing various types of polyhydroxyalkanoate polymers. Phospholipids and lipid A in membranes of P. putida play important roles in stress responses, but detailed structural information of these lipids is not known. In this study, phospholipids and lipid A were isolated from P. putida KT2442, and their structures were analyzed using thin layer chromatography, high performance liquid chromatography, and electrospray ionization/mass spectrometry. Major phospholipids in P. putida KT2442 were phosphatidylethanolamine (79.9%), phosphatidylglycero1 (12.7%), and cardiolipin (7.4%), with C16:1 and/or C18:1 acyl chains. Four lipid A species were found in P. putida KT2442: two are hexa-acylated, and the other two are penta-acylated. Compared with lipid A of P. aeruginosa, P. putida lipid A has less hydroxylation on the secondary acyl chains and less modification. Therefore, P. putida lipid A could be used as a base structure to investigate lipid A modification of P. aeruginosa for understanding its pathogenesis.

Roles of bacterial membrane vesicles

Outer membrane vesicles (OMVs) are released from the outer membrane of Gram-negative bacteria. Moreover, Gram-positive bacteria also produce membrane-derived vesicles. As OMVs transport several bacterial components, especially from the cell envelope, their interaction with the host cell, with other bacteria or as immunogens, have been studied intensely. Several functions have been ascribed to OMVs, especially those related to the transport of virulence factors, antigenic protein composition, and development as acellular vaccines. In this work, we review some of the recent findings about OMVs produced by specific pathogenic bacterial species.

Characterization of the key antigenic components of pertussis vaccine based on outer membrane vesicles

Pertussis has resurged during the last two decades in different countries. In particular in the 2010-2013 period large outbreaks were detected in US, Australia, UK and The Netherlands with significant mortality in infants. The epidemiological situation of pertussis points out the need to develop new vaccines and in this regard we previously developed a new vaccine based on outer membrane vesicles (OMVs) which have been shown to be safe and to induce protection in mice. Here we have further investigated the properties of OMVs vaccines; in particular we studied the contribution of pertussis toxin (PTx) and pertactin (Prn) in OMVs-mediated protection against pertussis. PTx-deficient OMVs and Prn-deficient OMVs were obtained from defective Bordetella pertussis mutants. The absence of PTx or Prn did compromise the protective capacity of the OMVs formulated as Tdap vaccine. Whereas the protective efficacy of the PTx-deficient OMVs in mice was comparable to Prn-deficient OMVs, the protective capacity of both of them was significantly impaired when it was compared with the wild type OMVs. Interestingly, using OMVs obtained from a B. pertussis strain which does not express any of the virulence factors but expresses the avirulent phenotype; we observed that the protective ability of such OMVs was lower than that of OMVs obtained from virulent B. pertussis phase. However, it was surprising that although the protective capacity of avirulent OMVs was lower, they were still protective in the used mice model. These results allow us to hypothesize that OMVs from avirulent phase shares protective components with all OMVs assayed. Using an immune proteomic strategy we identified some common components that could play an important role in protection against pertussis.

Bacterial outer membrane vesicles and vaccine applications

Vaccines based on outer membrane vesicles (OMV) were developed more than 20 years ago against Neisseria meningitidis serogroup B. These nano-sized structures exhibit remarkable potential for immunomodulation of immune responses and delivery of meningococcal antigens or unrelated antigens incorporated into the vesicle structure. This paper reviews different applications in OMV Research and Development (R&D) and provides examples of OMV developed and evaluated at the Finlay Institute in Cuba. A Good Manufacturing Practice (GMP) process was developed at the Finlay Institute to produce OMV from N. meningitidis serogroup B (dOMVB) using detergent extraction. Subsequently, OMV from N. meningitidis, serogroup A (dOMVA), serogroup W (dOMVW), and serogroup X (dOMVX) were obtained using this process. More recently, the extraction process has also been applied effectively for obtaining OMV on a research scale from Vibrio cholerae (dOMVC), Bordetella pertussis (dOMVBP), Mycobacterium smegmatis (dOMVSM), and BCG (dOMVBCG). The immunogenicity of the OMV has been evaluated for specific antibody induction, and together with functional bactericidal and challenge assays in mice has shown their protective potential. dOMVB has been evaluated with non-neisserial antigens, including with a herpes virus type 2 glycoprotein, ovalbumin, and allergens. In conclusion, OMV are proving to be more versatile than first conceived and remain an important technology for development of vaccine candidates.

Microbial biosynthesis of designer outer membrane vesicles

Outer membrane vesicles (OMVs) are nanoscale proteoliposomes that are ubiquitously secreted by Gram-negative bacteria. Interest in these bioparticles has escalated over the years, leading to discoveries regarding their composition, production, and vaccine potential. Given that many steps in vesicle biogenesis are 'engineerable,' it is now possible to tailor OMVs for specific applications. Such tailoring involves modifying the OMV-producing bacterium through protein, pathway, or genome engineering in a manner that specifically alters the final OMV product. For example, targeted deletion or upregulation of genes associated with the cell envelope can modulate vesicle production or remodel the composition of vesicle components such as lipopolysaccharide. Likewise, bacteria can be reprogrammed to incorporate heterologously expressed proteins into either the membrane or lumenal compartment of OMVs. We anticipate that further research in the field of OMV engineering will enable continued design and biosynthesis of specialized vesicles for numerous biotechnological purposes ranging from the delivery of vaccines to the deconstruction of cellulosic substrates.

Acellular pertussis vaccine based on outer membrane vesicles capable of conferring both long-lasting immunity and protection against different strain genotypes

Despite high vaccination coverage rates, pertussis continues to be a global concern, with increased incidence widely noted. The current pertussis epidemiologic situation has been mainly attributed to waning immunity and pathogen adaptation. To improve the disease control, a new generation of vaccines capable to overcome those weaknesses associated to the current vaccines need to be developed. Previously we have demonstrated that the outer membrane vesicles obtained from the recombinant Bordetella pertussis strain expressing PagL enzyme (OMVs(BpPagL)) are good vaccine candidates to protect against pertussis. In this work the OMVs(BpPagL) formulated with diphtheria and tetanus toxoids (Tdap(OMVsBpPagL)) was used to evaluate its capacity to offer protection against Argentinean clinical isolates and to induce long-term immunity. To these aims BALB/c mice were immunized with Tdap(OMVsBpPagL) and challenged with sublethal doses of the clinical isolate Bp106 selected as a representative circulating isolate. Comparisons with a current commercial Tdap vaccine used at a dose in which pertussis toxin level was equivalent to that of Tdap(OMVsBpPagL) were performed. With the normalized doses of both vaccines we observed that Tdap(OMVsBpPagL) protected against the clinical isolate infection, whereas current commercial Tdap vaccine showed little protection against such pathogen. Regarding long-term immunity we observed that the Tdap(OMVsBpPagL) protective capacity against the recommended WHO reference strain persisted at least 9 months. In agreement with these results Tdap(OMVsBpPagL) induced Th1 and Th2 immune response. In contrast, commercial Tdap induced Th2 but weak Th1 responses. All results presented here showed that Tdap(OMVsBpPagL) is an interesting formulation to be considered for the development of novel acellular multi-antigen vaccine.

The pertussis problem

Pertussis is resurgent, and many cases are occurring in vaccinated children and adolescents. In countries using acellular vaccines, waning immunity is at least part of the problem. This article discusses possible improvements in those vaccines.

Pathogen-like particles: biomimetic vaccine carriers engineered at the nanoscale

Vaccine adjuvants are an essential component of vaccine design, helping to generate immunity to pathogen antigens in the absence of infection. Recent advances in nanoscale engineering have created a new class of particulate bionanotechnology that uses biomimicry to better integrate adjuvant and antigen. These pathogen-like particles, or PLPs, can come from a variety of sources, ranging from fully synthetic platforms to biologically derived, self-assembling systems. By employing molecularly engineered targeting and stimulation of key immune cells, recent studies utilizing PLPs as vaccine delivery platforms have shown great promise against high-impact, unsolved vaccine targets ranging from bacterial and viral pathogens to cancer and addiction.

Outer membrane vesicles derived from Bordetella parapertussis as an acellular vaccine against Bordetella parapertussis and Bordetella pertussis infection

Bordetella parapertussis, a close related species of B. pertussis, can also cause the disease named pertussis or whooping cough. The number of cases caused by this related pathogen has risen sustained in the last years. The widely used cellular (wP) or acellular (aP) pertussis vaccines have little or no efficacy against B. parapertussis. In an effort to devise an effective acellular vaccine against B. parapertussis infection, outer membrane vesicles (OMVs) were obtained from B. parapertussis. Proteomic analysis of the resulting OMVs, designated OMVsBpp, evidenced the presence of several surface immunogens including pertactin. The characterized OMVsBpp were used in murine B. parapertussis intranasal challenge model to examine their protective capacity when administered by systemic route. Immunized BALB/c mice were challenged with sublethal doses of B. parapertussis. Significant differences between immunized animals and the negative control group were observed (p<0.001). OMVsBpp protected against B. parapertussis infection, whereas current commercial aP vaccine showed little protection against such pathogen. More interestingly, protection induced by OMVsBpp against B. pertussis was comparable to our previously designed vaccine consisting in OMVs derived from B. pertussis (OMVsBp). For these experiments we used as a positive control the current commercial aP vaccine in high dose. As expected aP offered protection against B. pertussis in mice. Altogether the results presented here showed that the OMVs from B. parapertussis are an attractive vaccine candidate to protect against whooping cough induced by B. parapertussis but also by B. pertussis.

Re-emergence of pertussis: what are the solutions?

Whooping cough, due to Bordetella pertussis and Bordetella parapertussis, is an important cause of childhood morbidity and mortality. Despite widespread pertussis immunization in childhood, there are an estimated 50 million cases and 300,000 deaths due to pertussis globally each year. Infants who are too young to be vaccinated, children who are partially vaccinated and fully-vaccinated persons with waning immunity are especially vulnerable to disease. Since pertussis is one of the vaccine-preventable diseases on the rise, additional vaccine approaches are needed. These approaches include vaccination of newborns, additional booster doses for older adolescents and adults, and immunization of pregnant women with existing vaccines. Innovative new vaccines are also being studied. Each of these options will be discussed and their potential impact on pertussis control assessed.

Recognition of lipid A variants by the TLR4-MD-2 receptor complex

Lipopolysaccharide (LPS) is a component of the outer membrane of almost all Gram-negative bacteria and consists of lipid A, core sugars, and O-antigen. LPS is recognized by Toll-like receptor 4 (TLR4) and MD-2 on host innate immune cells and can signal to activate the transcription factor NFκB, leading to the production of pro-inflammatory cytokines that initiate and shape the adaptive immune response. Most of what is known about how LPS is recognized by the TLR4-MD-2 receptor complex on animal cells has been studied using Escherichia coli lipid A, which is a strong agonist of TLR4 signaling. Recent work from several groups, including our own, has shown that several important pathogenic bacteria can modify their LPS or lipid A molecules in ways that significantly alter TLR4 signaling to NFκB. Thus, it has been hypothesized that expression of lipid A variants is one mechanism by which pathogens modulate or evade the host immune response. Additionally, several key differences in the amino acid sequences of human and mouse TLR4-MD-2 receptors have been shown to alter the ability to recognize these variations in lipid A, suggesting a host-specific effect on the immune response to these pathogens. In this review, we provide an overview of lipid A variants from several human pathogens, how the basic structure of lipid A is recognized by mouse and human TLR4-MD-2 receptor complexes, as well as how alteration of this pattern affects its recognition by TLR4 and impacts the downstream immune response.

New technologies in developing recombinant attenuated Salmonella vaccine vectors

Recombinant attenuated Salmonella vaccine (RASV) vectors producing recombinant gene-encoded protective antigens should have special traits. These features ensure that the vaccines survive stresses encountered in the gastrointestinal tract following oral vaccination to colonize lymphoid tissues without causing disease symptoms and to result in induction of long-lasting protective immune responses. We recently described ways to achieve these goals by using regulated delayed in vivo attenuation and regulated delayed in vivo antigen synthesis, enabling RASVs to efficiently colonize effector lymphoid tissues and to serve as factories to synthesize protective antigens that induce higher protective immune responses. We also developed some additional new strategies to increase vaccine safety and efficiency. Modification of lipid A can reduce the inflammatory responses without compromising the vaccine efficiency. Outer membrane vesicles (OMVs) from Salmonella-containing heterologous protective antigens can be used to increase vaccine efficiency. A dual-plasmid system, possessing Asd+ and DadB+ selection markers, each specifying a different protective antigen, can be used to develop multivalent live vaccines. These new technologies have been adopted to develop a novel, low-cost RASV synthesizing multiple protective pneumococcal protein antigens that could be safe for newborns/infants and induce protective immunity to diverse Streptococcus pneumoniae serotypes after oral immunization.

New pertussis vaccination approaches: en route to protect newborns?

Pertussis or whooping cough is a life-threatening childhood disease, particularly severe during the first months of life, although adolescent and adult pertussis is increasingly more noted. General vaccination has tremendously reduced its incidence but has failed to bring it completely under control. In fact, it remains one of the most poorly controlled vaccine-preventable diseases in the world. New vaccination strategies are thus being explored. These include vaccination of pregnant mothers to transmit protective antibodies to the offspring, a cocooning strategy to prevent the transmission of the disease from family members to the newborn and neonatal vaccination. All have their inherent limitations, and improved vaccines are urgently needed. Two types of pertussis vaccines are currently available, whole-cell, first-generation and second-generation, acellular vaccines, with an improved safety profile. Attempts have been made to discover additional protective antigens to the 1-5 currently included in the acellular vaccines or to include new adjuvants. Recently, a live attenuated nasal Bordetella pertussis vaccine has been developed and undergone first-in-man clinical trials. However, as promising as it may be, in order to protect infants against severe disease, a single approach may not be sufficient, and multiple strategies applied in a concerted fashion may ultimately be required.

Visualization of murine intranasal dosing efficiency using luminescent Francisella tularensis: effect of instillation volume and form of anesthesia

Intranasal instillation is a widely used procedure for pneumonic delivery of drugs, vaccine candidates, or infectious agents into the respiratory tract of research mice. However, there is a paucity of published literature describing the efficiency of this delivery technique. In this report we have used the murine model of tularemia, with Francisella tularensis live vaccine strain (FTLVS) infection, to evaluate the efficiency of pneumonic delivery via intranasal dosing performed either with differing instillation volumes or different types of anesthesia. FTLVS was rendered luminescent via transformation with a reporter plasmid that constitutively expressed the Photorhabdus luminescens lux operon from a Francisella promoter. We then used an IVIS Spectrum whole animal imaging system to visualize FT dissemination at various time points following intranasal instillation. We found that instillation of FT in a dose volume of 10 µl routinely resulted in infection of the upper airways but failed to initiate infection of the pulmonary compartment. Efficient delivery of FT into the lungs via intranasal instillation required a dose volume of 50 µl or more. These studies also demonstrated that intranasal instillation was significantly more efficient for pneumonic delivery of FTLVS in mice that had been anesthetized with inhaled (isoflurane) vs. parenteral (ketamine/xylazine) anesthesia. The collective results underscore the need for researchers to consider both the dose volume and the anesthesia type when either performing pneumonic delivery via intranasal instillation, or when comparing studies that employed this technique.

A new cloning system based on the OprI lipoprotein for the production of recombinant bacterial cell wall-derived immunogenic formulations

The conjugation of antigens with ligands of pattern recognition receptors (PRR) is emerging as a promising strategy for the modulation of specific immunity. Here, we describe a new Escherichia coli system for the cloning and expression of heterologous antigens in fusion with the OprI lipoprotein, a TLR ligand from the Pseudomonas aeruginosa outer membrane (OM). Analysis of the OprI expressed by this system reveals a triacylated lipid moiety mainly composed by palmitic acid residues. By offering a tight regulation of expression and allowing for antigen purification by metal affinity chromatography, the new system circumvents the major drawbacks of former versions. In addition, the anchoring of OprI to the OM of the host cell is further explored for the production of novel recombinant bacterial cell wall-derived formulations (OM fragments and OM vesicles) with distinct potential for PRR activation. As an example, the African swine fever virus ORF A104R was cloned and the recombinant antigen was obtained in the three formulations. Overall, our results validate a new system suitable for the production of immunogenic formulations that can be used for the development of experimental vaccines and for studies on the modulation of acquired immunity.

Discovery of Salmonella virulence factors translocated via outer membrane vesicles to murine macrophages

Salmonella enterica serovar Typhimurium, an intracellular pathogen and leading cause of food-borne illness, encodes a plethora of virulence effectors. Salmonella virulence factors are translocated into host cells and manipulate host cellular activities, providing a more hospitable environment for bacterial proliferation. In this study, we report a new set of virulence factors that is translocated into the host cytoplasm via bacterial outer membrane vesicles (OMV). PagK (or PagK1), PagJ, and STM2585A (or PagK2) are small proteins composed of ∼70 amino acids and have high sequence homology to each other (>85% identity). Salmonella lacking all three homologues was attenuated for virulence in a mouse infection model, suggesting at least partial functional redundancy among the homologues. While each homologue was translocated into the macrophage cytoplasm, their translocation was independent of all three Salmonella gene-encoded type III secretion systems (T3SSs)-Salmonella pathogenicity island 1 (SPI-1) T3SS, SPI-2 T3SS, and the flagellar system. Selected methods, including direct microscopy, demonstrated that the PagK-homologous proteins were secreted through OMV, which were enriched with lipopolysaccharide (LPS) and outer membrane proteins. Vesicles produced by intracellular bacteria also contained lysosome-associated membrane protein 1 (LAMP1), suggesting the possibility of OMV convergence with host cellular components during intracellular trafficking. This study identified novel Salmonella virulence factors secreted via OMV and demonstrated that OMV can function as a vehicle to transfer virulence determinants to the cytoplasm of the infected host cell.