High Vaccine Efficacy against Shigellosis of Recombinant NoninvasiveShigellaMutant That ExpressesYersiniaInvasin

Shigella infection and host cell death: a double-edged sword for the host and pathogen survival

In response to bacterial infection, epithelial cells undergo several types of cell death, including apoptosis, necrosis, pyroptosis, and necroptosis, which serve to expel the infected cells and activate the innate and acquired immune responses. Shigella initially invades macrophages and subsequently surrounding enterocytes; the pathogen executes macrophage cell death but prevents epithelial cell death in order to maintain its foothold for replication. To this end, Shigella delivers versatile effector proteins via the type III secretion system (T3SS), allowing it to efficiently colonize the intestinal epithelium. In this article, we review insights into the mechanisms underlying circumvention of the host cell death by Shigella, as an example of bacterial fine-tuning of host cell death pathways.

Enhanced protective immune response to PCV2 adenovirus vaccine by fusion expression of Cap protein with InvC in pigs

The major immunogenic protein capsid (Cap) of porcine circovirus type 2 (PCV2) is critical to induce neutralizing antibodies and protective immune response against PCV2 infection. This study was conducted to investigate the immune response of recombinant adenovirus expressing PCV2b Cap and C-terminal domain of Yersinia pseudotuberculosis invasin (Cap-InvC) fusion protein in pigs. The recombinant adenovirus rAd-Cap-InvC, rAd-Cap and rAd were generated and used to immunize pigs. The phosphate-buffered saline was used as negative control. The specific antibodies levels in rAd-Cap-InvC and ZJ/C-strain vaccine groups were higher than that of rAd-Cap group (p < 0.05), and the neutralization antibody titer in rAd-Cap-InvC group was significantly higher than those of other groups during 21–42 days post-immunization (DPI). Moreover, lymphocyte proliferative level, interferon-γ and interleukin-13 levels in rAd-Cap-InvC group were increased compared to rAd-Cap group (p < 0.05). After virulent challenge, viruses were not detected from the blood samples in rAd-Cap-InvC and ZJ/C-strain vaccine groups after 49 DPI. And the respiratory symptom, rectal temperature, lung lesion and lymph node lesion were minimal and similar in the ZJ/C-strain and rAd-Cap-InVC groups. In conclusion, our results demonstrated that rAd-Cap-InvC was more efficiently to stimulate the production of antibody and protect pigs from PCV2 infection. We inferred that InvC is a good candidate gene for further development and application of PCV2 genetic engineering vaccine.

M cell targeting engineered biomaterials for effective vaccination

Vaccines are one of the greatest medical interventions of all time and have been successful in controlling and eliminating a myriad of diseases over the past two centuries. Among several vaccination strategies, mucosal vaccines have wide clinical applications and attract considerable interest in research, showing potential as innovative and novel therapeutics. In mucosal vaccination, targeting (microfold) M cells is a frontline prerequisite for inducing effective antigen-specific immunostimulatory effects. In this review, we primarily focus on materials engineered for use as vaccine delivery platforms to target M cells. We also describe potential M cell targeting areas, methods to overcome current challenges and limitations of the field. Furthermore, we present the potential of biomaterials engineering as well as various natural and synthetic delivery technologies to overcome the challenges of M cell targeting, all of which are absent in current literature. Finally, we briefly discuss manufacturing and regulatory processes to bring a robust perspective on the feasibility and potential of this next-generation vaccine technology.

Stress-induced host membrane remodeling protects from infection by non-motile bacterial pathogens

While mucosal inflammation is a major source of stress during enteropathogen infection, it remains to be fully elucidated how the host benefits from this environment to clear the pathogen. Here, we show that host stress induced by different stimuli mimicking inflammatory conditions strongly reduces the binding of Shigella flexneri to epithelial cells. Mechanistically, stress activates acid sphingomyelinase leading to host membrane remodeling. Consequently, knockdown or pharmacological inhibition of the acid sphingomyelinase blunts the stress-dependent inhibition of Shigella binding to host cells. Interestingly, stress caused by intracellular Shigella replication also results in remodeling of the host cell membrane, in vitro and in vivo, which precludes re-infection by this and other non-motile pathogens. In contrast, Salmonella Typhimurium overcomes the shortage of permissive entry sites by gathering effectively at the remaining platforms through its flagellar motility. Overall, our findings reveal host membrane remodeling as a novel stress-responsive cell-autonomous defense mechanism that protects epithelial cells from infection by non-motile bacterial pathogens.

Immunogenic evaluation of chimeric recombinant protein against ETEC, EHEC and Shigella

Diarrheal diseases still remain health problem worldwide and out of many bacteria responsible for, Shigella and pathogenic Escherichia cause the most diarrheas in the world. Shigellacause bacterial dysenteries and shigellosis through invasion where the most effective proteins for pathogenesis is Ipac. Critical virulence protein for ETEC infection is CFA/I with two subunits called cfab and cfae. . Attachment of EHEC is the main step of infection and the protein Intimin plays the key role in this function. Protection against the vast majority of responsible pathogens of diarrheas requires development of the combination vaccine against Shigella, ETEC and EHEC. In the present study, a multisubunitprotein (CII) containing immunologically significant parts of CfaB, IpaC and Intimin was designed. The chimeric gene (CII) was codon optimized and analyzed with different bioinformatic servers, then synthesized and expressed in E. coli. Mice, Guinea pig and, Caco-2 Cell line were used as challenge models for EHEC, shigella and ETEC respectively. The chimeric protein induced significant immune response and therefore could be a suitable vaccine candidate against these three pathogens.

Co-expression of the C-terminal domain of Yersinia enterocolitica invasin enhances the efficacy of classical swine-fever-vectored vaccine based on human adenovirus

The use of adenovirus vector-based vaccines is a promising approach for generating antigen-specific immune responses. Improving vaccine potency is necessary in other approaches to address their inadequate protection for the majority of infectious diseases. This study is the first to reconstruct a recombinant replication-defective human adenovirus co-expressing E2 and invasin C-terminal (InvC) glycoproteins (rAd-E2-InvC). rAd-E2-InvC with 2 x 10(6) TCID50 was intramuscularly administered two times to CSFV-free pigs at 14 day intervals. No adverse clinical reactions were observed in any of the pigs after the vaccination. The CSFV E2-specific antibody titer was significantly higher in the rAd-E2-InvC group than that in the rAdV-E2 group as measured by NPLA and blocking ELISA. Pigs immunized with rAd-E2-InvC were completely protected against lethal challenge. Neither CSFV RNA nor pathological changes were detected in the tissues after CSFV challenge. These results demonstrate that rAd-E2-InvC could be an alternative to the existing CSF vaccine. Moreover, InvC that acts as an adjuvant could enhance the immunogenicity of rAdV-E2 and induce high CSFV E2-specific antibody titer and protection level.

Antigen Delivery System II

This chapter reviews papers mostly written since 2005 that report results using live attenuated bacterial vectors to deliver after administration through mucosal surfaces, protective antigens, and DNA vaccines, encoding protective antigens to induce immune responses and/or protective immunity to pathogens that colonize on or invade through mucosal surfaces. Papers that report use of such vaccine vector systems for parenteral vaccination or to deal with nonmucosal pathogens or do not address induction of mucosal antibody and/or cellular immune responses are not reviewed.

Impact of dynasore an inhibitor of dynamin II on Shigella flexneri infection

Shigella flexneri remains a significant human pathogen due to high morbidity among children < 5 years in developing countries. One of the key features of Shigella infection is the ability of the bacterium to initiate actin tail polymerisation to disseminate into neighbouring cells. Dynamin II is associated with the old pole of the bacteria that is associated with F-actin tail formation. Dynamin II inhibition with dynasore as well as siRNA knockdown significantly reduced Shigella cell to cell spreading in vitro. The ocular mouse Sereny model was used to determine if dynasore could delay the progression of Shigella infection in vivo. While dynasore did not reduce ocular inflammation, it did provide significant protection against weight loss. Therefore dynasore's effects in vivo are unlikely to be related to the inhibition of cell spreading observed in vitro. We found that dynasore decreased S. flexneri-induced HeLa cell death in vitro which may explain the protective effect observed in vivo. These results suggest the administration of dynasore or a similar compound during Shigella infection could be a potential intervention strategy to alleviate disease symptoms.

Shigella IpaH0722 E3 ubiquitin ligase effector targets TRAF2 to inhibit PKC-NF-κB activity in invaded epithelial cells

NF-κB plays a central role in modulating innate immune responses to bacterial infections. Therefore, many bacterial pathogens deploy multiple mechanisms to counteract NF-κB activation. The invasion of and subsequent replication of Shigella within epithelial cells is recognized by various pathogen recognition receptors as pathogen-associated molecular patterns. These receptors trigger innate defense mechanisms via the activation of the NF-κB signaling pathway. Here, we show the inhibition of the NF-κB activation by the delivery of the IpaH E3 ubiquitin ligase family member IpaH0722 using Shigella's type III secretion system. IpaH0722 dampens the acute inflammatory response by preferentially inhibiting the PKC-mediated activation of NF-κB by ubiquitinating TRAF2, a molecule downstream of PKC, and by promoting its proteasome-dependent degradation.

In response to bacterial infection, host cells induce a plethora of innate immune responses to combat the infection. However, many bacterial pathogens have developed sophisticated mechanisms to evade the host's immune system. Because NF-κB is crucial for innate immune responses against bacterial infection, bacterial pathogens deploy multiple countermeasures to inhibit NF-κB activation. The invasion and replication of Shigella within host cells results in cellular damage and the production of bacterial components that trigger NF-κB activation. Here, we show that the Shigella type III secretion system (T3SS) effector IpaH0722, a member of the IpaH E3 ubiquitin ligase family, inhibits NF-κB activation during Shigella infection. IpaH0722 preferentially targets the PKC–NF-κB pathway, which is activated in response to danger signals caused by disruption of the phagosomal membrane during the dissemination of Shigella into the cytoplasm. IpaH0722 inhibits NF-κB activation by targeting TRAF2, which lies downstream of PKC, for ubiquitination and proteasome-dependent degradation.

Bacterial invasion factors: tools for crossing biological barriers and drug delivery?

The oral route is the preferential route of drug delivery in humans. However, effective delivery through the gastrointestinal tract is often hampered by the low permeability of the intestinal epithelium. One possibility to overcome this problem is the encapsulation of drugs inside nanoparticulate systems, containing targeting moieties with cell invasive properties. The bioinvasive features of the delivery system could be provided by the attachment of bacterial invasion factors, which promote efficient uptake into host cells and mediate rapid transcytosis of the pathogen through the intestinal epithelium. This review gives an overview of bacterial invasion systems. The molecular structure and function of suitable bacterial invasins, their relative values as targeting agents and possible pitfalls of their use are described. The potential of bioinvasive drug delivery systems is mainly presented on the basis of the well-characterized Yersinia invasin protein, which enters M cells to gain access to subepithelial layers of the gastrointestinal tract, but alternative approaches and future prospects for oral drug delivery are also discussed.

Two live attenuated Shigella flexneri 2a strains WRSf2G12 and WRSf2G15: a new combination of gene deletions for 2nd generation live attenuated vaccine candidates

Shigella infections are a major cause of inflammatory diarrhea and dysentery worldwide. First-generation virG-based live attenuated Shigella strains have been successfully tested in phase I and II clinical trials and are a leading approach for Shigella vaccine development. Additional gene deletions in senA, senB and msbB2 have been engineered into second-generation virG-based Shigella flexneri 2a strains producing WRSf2G12 and WRSf2G15. Both strains harbor a unique combination of gene deletions designed to increase the safety of live Shigella vaccines. WRSf2G12 and WRSf2G15 are genetically stable and highly attenuated in both cell culture and animal models of infection. Ocular immunization of guinea pigs with either strain induces robust systemic and mucosal immune responses that protect against homologous challenge with wild-type Shigella. The data support further evaluation of the second-generation strains in a phase I clinical trial.

Th17 cells are the dominant T cell subtype primed by Shigella flexneri mediating protective immunity

The T cell response to Shigella, the causative agent of bacillary dysentery, remains poorly understood. Using a murine model of infection, we report that Shigella flexneri primes predominately IL-17A- and IL-22-producing Th17 cells. Shigella-specific Th1 cells are only significantly induced on secondary infection, whereas specific Th2 and CD8(+) T cells are undetectable. Apart from Th17 cells that are primed in a MHC class II- and IL-6-dependent, but IL12/23p40-independent manner, we identified gammadelta T cells as an additional but minor source of IL-17A. Priming of IL-17A(+) gammadelta T cells is dependent on IL12/23p40, but independent of MHC-class II and IL-6. Th17 cells have emerged as important players in inflammatory, autoimmune, and infectious diseases. Among the yet unresolved questions is their role in long-term immunity to pathogens. In this study, we show that the elicited S. flexneri-specific Th17 pool gives rise to an enhanced recall response up to 12 mo after priming, suggesting the presence of a long-term memory state. The clearance of primary infection is impaired in the absence of T cells, but independently of IL-17A. However, after reinfection, IL-17A produced by S. flexneri-specific Th17 cells becomes important to ultimately restrict bacterial growth. These findings bring new insights into the adaptive immune response to Shigella infection and highlight the importance of pathogen-specific Th17 cell immunity for secondary immune protection.

Virulence, inflammatory potential, and adaptive immunity induced by Shigella flexneri msbB mutants

The ability of genetically detoxified lipopolysaccharide (LPS) to stimulate adaptive immune responses is an ongoing area of investigation with significant consequences for the development of safe and effective bacterial vaccines and adjuvants. One approach to genetic detoxification is the deletion of genes whose products modify LPS. The msbB1 and msbB2 genes, which encode late acyltransferases, were deleted in the Shigella flexneri 2a human challenge strain 2457T to evaluate the virulence, inflammatory potential, and acquired immunity induced by strains producing underacylated lipid A. Consistent with a reduced endotoxic potential, S. flexneri 2a msbB mutants were attenuated in an acute mouse pulmonary challenge model. Attenuation correlated with decreases in the production of proinflammatory cytokines and in chemokine release without significant changes in lung histopathology. The levels of specific proinflammatory cytokines (interleukin-1beta [IL-1beta], macrophage inflammatory protein 1alpha [MIP-1alpha], and tumor necrosis factor alpha [TNF-alpha]) were also significantly reduced after infection of mouse macrophages with either single or double msbB mutants. Surprisingly, the msbB double mutant displayed defects in the ability to invade, replicate, and spread within epithelial cells. Complementation restored these phenotypes, but the exact nature of the defects was not determined. Acquired immunity and protective efficacy were also assayed in the mouse lung model, using a vaccination-challenge study. Both humoral and cellular responses were generally robust in msbB-immunized mice and afforded significant protection from lethal challenge. These data suggest that the loss of either msbB gene reduces the endotoxicity of Shigella LPS but does not coincide with a reduction in protective immune responses.

Shigellosis: the current status of vaccine development

PURPOSE OF REVIEW

Shigellosis, a major form of bacillary dysentery, is caused by infection with Shigella organisms. In poor countries, Shigella-caused dysentery is endemic and causes an estimated 163 million illness episodes annually and more than one million deaths. Although several strategies have been used to develop vaccines targeting shigellosis, none has been licensed for use outside China. Owing to the wide range of Shigella serotypes and subtypes, there is a need for a multivalent vaccine representing prevalent species and serotypes.

RECENT FINDINGS

Vaccine development has been limited by the lack of a suitable animal model for vaccine testing. This review discusses the most advanced strategies for Shigella vaccine development including live attenuated, conjugate, broad spectrum, and proteosome-based vaccines and describes current animal models under study.

SUMMARY

The greatest barrier to the use of vaccine against shigellosis in developing areas is poor immune responses to oral vaccines in children who have minimal maternal antibodies. Clinical studies of promising shigellosis vaccine candidates are urgently needed after confirmation of safety, immunogenicity, and protection in volunteer challenge models.

M cell-targeted delivery of vaccines and therapeutics

BACKGROUND

M (microfold or membranous) cells are specialised epithelial cells responsible for antigen sampling at the interface of mucosal surfaces and the environment. Their high transcytotic ability make M cells an attractive target for mucosally delivered vaccines and therapeutics.

OBJECTIVE

This brief review discusses the current state of M cell-targeted mucosal delivery systems and the potential of such delivery systems for the development of new vaccines and therapeutics against mucosal infectious and inflammatory diseases.

SCOPE

A variety of synthetic microparticles/nanoparticles have been developed and tested as vehicles for M cell-targeted mucosal drug and vaccine delivery. beta1 integrins, pathogen recognition receptors, specific carbohydrate residues and other M cell surface antigens have been exploited as potential targets for the delivery of mucosal vaccines and therapeutics.

CONCLUSION

Despite a considerable body of literature, much work still needs to be done before an effective M cell-targeted vaccine or therapeutic is developed.

Immunogenicity and efficacy of highly purified invasin complex vaccine from Shigella flexneri 2a

Development of a subunit vaccine for shigellosis requires identification of protective antigens and delivering these antigens in a manner that stimulates immunity comparable to that induced by natural infection. The Shigella invasin complex (Invaplex) vaccine is an ion-exchange-purified extract from virulent Shigella that consists of LPS and several other proteins, including the invasins IpaB and IpaC. Intranasal delivery of Invaplex stimulates protective immunity in small animal models for shigellosis. To identify the active component(s) of Invaplex responsible for its immunogenicity and efficacy, size-exclusion chromatography (SEC) was used to separate Invaplex into several different fractions. A high-molecular mass complex with a molecular mass between 669 MDa and 2 MDa consisted primarily of LPS, IpaB and IpaC and was considered to be a highly purified (HP) form of Invaplex. Using the mouse lung model to evaluate the immunogenicity and efficacy of the SEC fractions it was clearly demonstrated that the high-molecular mass complex of the invasins and LPS was responsible for the protective capacity of parent native Invaplex. Other smaller mass SEC fractions were mostly non-immunogenic and did not stimulate solid protection. In guinea pigs, the HP Invaplex stimulated an enhanced immune response as compared to the parent Invaplex and was fully protective. Isolation and characterization of the immunogenic and protective moiety within Invaplex will allow better standardization of the Invaplex product and may allow future development of an Invaplex assembled from purified components.

M-cells: origin, morphology and role in mucosal immunity and microbial pathogenesis

M-cells are specialized cells found in the follicle-associated epithelium of intestinal Peyer's patches of gut-associated lymphoid tissue and in isolated lymphoid follicles, appendix and in mucosal-associated lymphoid tissue sites outside the gastrointestinal tract. In the gastrointestinal tract, M-cells play an important role in transport of antigen from the lumen of the small intestine to mucosal lymphoid tissues, where processing and initiation of immune responses occur. Thus, M-cells act as gateways to the mucosal immune system and this function has been exploited by many invading pathogens. Understanding the mechanism by which M-cells sample antigen will inform the design of oral vaccines with improved efficacy in priming mucosal and systemic immune responses. In this review, the origin and morphology of M-cells, and their role in mucosal immunity and pathogenesis of infections are discussed.

Type III secretion systems and disease

Type III secretion systems (T3SSs) are complex bacterial structures that provide gram-negative pathogens with a unique virulence mechanism enabling them to inject bacterial effector proteins directly into the host cell cytoplasm, bypassing the extracellular milieu. Although the effector proteins vary among different T3SS pathogens, common pathogenic mechanisms emerge, including interference with the host cell cytoskeleton to promote attachment and invasion, interference with cellular trafficking processes, cytotoxicity and barrier dysfunction, and immune system subversion. The activity of the T3SSs correlates closely with infection progression and outcome, both in animal models and in human infection. Therefore, to facilitate patient care and improve outcomes, it is important to understand the T3SS-mediated virulence processes and to target T3SSs in therapeutic and prophylactic development efforts.

Yersinia enterocolitica: subversion of adaptive immunity and implications for vaccine development

Enteric Yersinia spp. invade Peyer's patches, disseminate to lymphoid tissues, and induce mucosal and systemic immune responses. Many virulence factors of Yersinia enterocolitica have been investigated in detail and were found to act on host cells involved in innate and adaptive immunity. Recent work explored as to whether attenuated Y. enterocolitica or recombinant components of Y. enterocolitica can be used as tools for vaccination. We and others have tested whether by means of the type three secretion system in attenuated Y. enterocolitica strains antigens might be delivered to antigen-presenting cells in order to induce CD8 and CD4 T cell responses. Alternatively, recombinant components of Y. enterocolitica such as invasin protein which binds to beta1 integrins of host cells have been tested for their ability to target antigen along with microparticles (fused to invasin) to antigen-presenting cells and to act as adjuvant. The work summarized in this article demonstrates that Y. enterocolitica and its components might be useful tools for novel vaccination strategies; in fact, invasin when fused to antigen and coated to microparticles might induce both CD4 and CD8 T cell responses. Likewise, attenuated Y. enterocolitica live carrier strains were reported to induce both CD8 and some CD4 T cell responses. However, we need to know more about how Y. enterocolitica subverts functions of antigen-presenting cells in order to design mutants with optimized antigen delivery features and deletion in those virulence factor that contribute to subversion of innate or adaptive immune responses.

Shigella chromosomal IpaH proteins are secreted via the type III secretion system and act as effectors

Shigella possess 220 kb plasmid, and the major virulence determinants, called effectors, and the type III secretion system (TTSS) are exclusively encoded by the plasmid. The genome sequences of S. flexneri strains indicate that several ipaH family genes are located on both the plasmid and the chromosome, but whether their chromosomal IpaH cognates can be secreted from Shigella remains unknown. Here we report that S. flexneri strain, YSH6000 encodes seven ipaH cognate genes on the chromosome and that the IpaH proteins are secreted via the TTSS. The secretion kinetics of IpaH proteins by bacteria, however, showed delay compared with those of IpaB, IpaC and IpaD. Expression of the each mRNA of ipaH in Shigella was increased after bacterial entry into epithelial cells, and the IpaH proteins were secreted by intracellular bacteria. Although individual chromosomal ipaH deletion mutants showed no appreciable changes in the pathogenesis in a mouse pulmonary infection model, the DeltaipaH-null mutant, whose chromosome lacks all ipaH genes, was attenuated to mice lethality. Indeed, the histological examination for mouse lungs infected with the DeltaipaH-null showed a greater inflammatory response than induced by wild-type Shigella, suggesting that the chromosomal IpaH proteins act synergistically as effectors to modulate the host inflammatory responses.