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Lu T, Das S, Howlader DR, Picking WD, Picking WL. Shigella Vaccines: The Continuing Unmet Challenge. Int J Mol Sci 2024; 25:4329. [PMID: 38673913 PMCID: PMC11050647 DOI: 10.3390/ijms25084329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2024] [Revised: 04/09/2024] [Accepted: 04/11/2024] [Indexed: 04/28/2024] Open
Abstract
Shigellosis is a severe gastrointestinal disease that annually affects approximately 270 million individuals globally. It has particularly high morbidity and mortality in low-income regions; however, it is not confined to these regions and occurs in high-income nations when conditions allow. The ill effects of shigellosis are at their highest in children ages 2 to 5, with survivors often exhibiting impaired growth due to infection-induced malnutrition. The escalating threat of antibiotic resistance further amplifies shigellosis as a serious public health concern. This review explores Shigella pathology, with a primary focus on the status of Shigella vaccine candidates. These candidates include killed whole-cells, live attenuated organisms, LPS-based, and subunit vaccines. The strengths and weaknesses of each vaccination strategy are considered. The discussion includes potential Shigella immunogens, such as LPS, conserved T3SS proteins, outer membrane proteins, diverse animal models used in Shigella vaccine research, and innovative vaccine development approaches. Additionally, this review addresses ongoing challenges that necessitate action toward advancing effective Shigella prevention and control measures.
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Affiliation(s)
- Ti Lu
- Department of Veterinary Pathobiology and Bond Life Science Center, University of Missouri, Columbia, MO 65201, USA; (D.R.H.); (W.D.P.)
| | - Sayan Das
- Department of Microbial Pathogenesis, School of Dentistry, University of Maryland, Baltimore, MD 21201, USA;
| | - Debaki R. Howlader
- Department of Veterinary Pathobiology and Bond Life Science Center, University of Missouri, Columbia, MO 65201, USA; (D.R.H.); (W.D.P.)
| | - William D. Picking
- Department of Veterinary Pathobiology and Bond Life Science Center, University of Missouri, Columbia, MO 65201, USA; (D.R.H.); (W.D.P.)
| | - Wendy L. Picking
- Department of Veterinary Pathobiology and Bond Life Science Center, University of Missouri, Columbia, MO 65201, USA; (D.R.H.); (W.D.P.)
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Desalegn G, Tamilselvi CS, Lemme-Dumit JM, Heine SJ, Dunn D, Ndungo E, Kapoor N, Oaks EV, Fairman J, Pasetti MF. Shigella virulence protein VirG is a broadly protective antigen and vaccine candidate. NPJ Vaccines 2024; 9:2. [PMID: 38167387 PMCID: PMC10761965 DOI: 10.1038/s41541-023-00797-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Accepted: 12/08/2023] [Indexed: 01/05/2024] Open
Abstract
Diarrhea caused by Shigella has been associated with high morbidity and mortality in young children worldwide. There are no licensed vaccines, and those clinically advanced have restricted coverage as they elicit serotype-specific immunity while disease is caused by multiple circulating serotypes. Our group had previously reported a close association between serum antibodies to the Shigella virulence factor VirG (or IcsA) and clinical protection in infected individuals. VirG is highly conserved among Shigella strains and appealing as a broad-spectrum vaccine candidate. In this study, we investigated the immunogenicity and protective capacity of VirG as a subunit vaccine in mice. The surface-exposed alpha (α) domain of VirG (VirGα) was produced as a recombinant protein. This region has almost identical immune reactivity to full-length VirG. Administered intramuscularly with alum, VirGα elicited robust immune responses and high protective efficacy against S. flexneri 2a and S. sonnei. Almost complete protection was afforded by VirGα given intranasally with the E. coli double mutant heat-labile toxin (dmLT). VirGα-specific antibodies recognized VirG expressed on live Shigella, and blocked Shigella adhesion and invasion to human colonic cells. These results show for the first time that VirGα is a promising cross-protective vaccine candidate to prevent Shigella infection.
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Affiliation(s)
- Girmay Desalegn
- Center for Vaccine Development and Global Health, University of Maryland School of Medicine, 685W. Baltimore Street, Baltimore, MD, 21201, USA
| | - Chitradevi S Tamilselvi
- Center for Vaccine Development and Global Health, University of Maryland School of Medicine, 685W. Baltimore Street, Baltimore, MD, 21201, USA
| | - Jose M Lemme-Dumit
- Center for Vaccine Development and Global Health, University of Maryland School of Medicine, 685W. Baltimore Street, Baltimore, MD, 21201, USA
| | - Shannon J Heine
- Center for Vaccine Development and Global Health, University of Maryland School of Medicine, 685W. Baltimore Street, Baltimore, MD, 21201, USA
| | - Dylan Dunn
- Center for Vaccine Development and Global Health, University of Maryland School of Medicine, 685W. Baltimore Street, Baltimore, MD, 21201, USA
| | - Esther Ndungo
- Center for Vaccine Development and Global Health, University of Maryland School of Medicine, 685W. Baltimore Street, Baltimore, MD, 21201, USA
| | - Neeraj Kapoor
- Vaxcyte, Inc., 825 Industrial Road, San Carlos, CA, 94070, USA
| | - Edwin V Oaks
- Patuxent Research and Consulting Group, 3106 Arrowhead Farm Rd, Gambrills, MD, 21054, USA
| | - Jeff Fairman
- Vaxcyte, Inc., 825 Industrial Road, San Carlos, CA, 94070, USA
| | - Marcela F Pasetti
- Center for Vaccine Development and Global Health, University of Maryland School of Medicine, 685W. Baltimore Street, Baltimore, MD, 21201, USA.
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Ranjbar R, Farahani A. Shigella: Antibiotic-Resistance Mechanisms And New Horizons For Treatment. Infect Drug Resist 2019; 12:3137-3167. [PMID: 31632102 PMCID: PMC6789722 DOI: 10.2147/idr.s219755] [Citation(s) in RCA: 75] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Accepted: 08/28/2019] [Indexed: 12/17/2022] Open
Abstract
Shigella spp. are a common cause of diarrheal disease and have remained an important pathogen responsible for increased rates of morbidity and mortality caused by dysentery each year around the globe. Antibiotic treatment of Shigella infections plays an essential role in reducing prevalence and death rates of the disease. However, treatment of these infections remains a challenge, due to the global rise in broad-spectrum resistance to many antibiotics. Drug resistance in Shigella spp. can result from many mechanisms, such as decrease in cellular permeability, extrusion of drugs by active efflux pumps, and overexpression of drug-modifying and -inactivating enzymes or target modification by mutation. Therefore, there is an increasing need for identification and evolution of alternative therapeutic strategies presenting innovative avenues against Shigella infections, as well as paying further attention to this infection. The current review focuses on various antibiotic-resistance mechanisms of Shigella spp. with a particular emphasis on epidemiology and new mechanisms of resistance and their acquisition, and also discusses the status of novel strategies for treatment of Shigella infection and vaccine candidates currently under evaluation in preclinical or clinical phases.
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Affiliation(s)
- Reza Ranjbar
- Molecular Biology Research Center, Systems Biology and Poisonings Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran
| | - Abbas Farahani
- Molecular Biology Research Center, Systems Biology and Poisonings Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran
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Abstract
Diarrheal diseases remain a leading cause of global childhood mortality and morbidity. Several recent epidemiological studies highlight the rate of diarrheal diseases in different parts of the world and draw attention to the impact on childhood growth and survival. Despite the well-documented global burden of diarrheal diseases, currently there are no combination diarrheal vaccines, only licensed vaccines for rotavirus and cholera, and Salmonella typhi-based vaccines for typhoid fever. The recognition of the impact of diarrheal episodes on infant growth, as seen in resource-poor countries, has spurred action from governmental and non-governmental agencies to accelerate research toward affordable and effective vaccines against diarrheal diseases. Both travelers and children in endemic countries will benefit from a combination diarrheal vaccine, but it can be argued that the greater proportion of any positive impact will be on the public health status of the latter. The history of combination pediatric vaccines indicate that monovalent or single disease vaccines are typically licensed first prior to formulation in a combination vaccine, and that the combinations themselves undergo periodic revision in response to need for improvement in safety or potential for wider coverage of important pediatric pathogens. Nevertheless combination pediatric vaccines have proven to be an effective tool in limiting or eradicating communicable childhood diseases worldwide. The landscape of diarrheal vaccine candidates indicates that there now several in active development that offer options for potential testing of combinations to combat those bacterial and viral pathogens responsible for the heaviest disease burden—rotavirus, ETEC, Shigella, Campylobacter, V. cholera and Salmonella.
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Affiliation(s)
- Malabi M Venkatesan
- a Bacterial Diseases Branch; Walter Reed Army Institute of Research ; Silver Spring , MD , USA
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O'Ryan M, Vidal R, del Canto F, Carlos Salazar J, Montero D. Vaccines for viral and bacterial pathogens causing acute gastroenteritis: Part II: Vaccines for Shigella, Salmonella, enterotoxigenic E. coli (ETEC) enterohemorragic E. coli (EHEC) and Campylobacter jejuni. Hum Vaccin Immunother 2015; 11:601-19. [PMID: 25715096 DOI: 10.1080/21645515.2015.1011578] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
In Part II we discuss the following bacterial pathogens: Shigella, Salmonella (non-typhoidal), diarrheogenic E. coli (enterotoxigenic and enterohemorragic) and Campylobacter jejuni. In contrast to the enteric viruses and Vibrio cholerae discussed in Part I of this series, for the bacterial pathogens described here there is only one licensed vaccine, developed primarily for Vibrio cholerae and which provides moderate protection against enterotoxigenic E. coli (ETEC) (Dukoral(®)), as well as a few additional candidates in advanced stages of development for ETEC and one candidate for Shigella spp. Numerous vaccine candidates in earlier stages of development are discussed.
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Key Words
- CFU, colony-forming units
- CFs, colonization factors
- CT, cholera toxin
- CT-B cholera toxin B subunit
- Campylobacter
- CtdB, cytolethal distending toxin subunit B
- E. coli
- EHEC
- EPEC, enteropathogenic E. coli
- ETEC
- ETEC, enterotoxigenic E. coli
- GEMS, Global enterics multicenter study
- HUS, hemolytic uremic syndrome
- IM, intramuscular
- IgA, immunoglobulin A
- IgG, immunoglobulin G
- IgM, immunoglobulin M
- LEE, locus of enterocyte effacement
- LPS, lipopolysaccharide
- LT, heat labile toxin
- LT-B
- OMV, outer membrane vesicles
- ST, heat stable toxin
- STEC
- STEC, shigatoxin producing E. coli
- STh, human heat stable toxin
- STp, porcine heat stable toxin
- Salmonella
- Shigella
- Stx, shigatoxin
- TTSS, type III secretion system
- V. cholera
- WHO, World Health Organization
- acute diarrhea
- dmLT, double mutant heat labile toxin
- enteric pathogens
- enterohemorrhagic E. coli
- gastroenteritis
- heat labile toxin B subunit
- norovirus
- rEPA, recombinant exoprotein A of Pseudomonas aeruginosa
- rotavirus
- vaccines
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Affiliation(s)
- Miguel O'Ryan
- a Microbiology and Mycology Program; Institute of Biomedical Sciences; Faculty of Medicine; Universidad de Chile; Santiago, Chile
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Jun JW, Kim HJ, Yun SK, Chai JY, Lee BC, Park SC. Isolation and Comparative Genomic Analysis of T1-Like Shigella Bacteriophage pSf-2. Curr Microbiol 2015; 72:235-41. [PMID: 26612033 DOI: 10.1007/s00284-015-0935-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Accepted: 09/23/2015] [Indexed: 01/21/2023]
Abstract
The increasing prevalence of antibiotic-resistant Shigella sp. emphasizes that alternatives to conventional antibiotics are needed. Siphoviridae bacteriophage (phage), pSf-2, infecting S. flexneri ATCC(®) 12022 was isolated from Geolpocheon stream in Korea. Morphological analysis by transmission electron microscopy revealed that pSf-2 has a head of about 57 ± 4 nm in diameter with a long tail of 136 ± 3 nm in length and 15 ± 2 nm in width. One-step growth analysis revealed that pSf-2 has latent period of 30 min and burst size of 16 PFU/infected cell. The DNA genome of pSf-2 is composed of 50,109 bp with a G+C content of 45.44 %. The genome encodes 83 putative ORFs, 19 putative promoters, and 23 transcriptional terminator regions. Genome sequence analysis of pSf-2 and comparative analysis with the homologous T1-like Shigella phages, Shfl1 and pSf-1, revealed that pSf-2 is a novel T1-like Shigella phage. These results showed that pSf-2 might have a high potential as a biocontrol agent to control shigellosis. Also, the genomic information may lead to further understanding of phage biodiversity, especially T1-like phages.
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Affiliation(s)
- Jin Woo Jun
- College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul, 151-742, South Korea
| | - Hyoun Joong Kim
- College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul, 151-742, South Korea
| | - Sae Kil Yun
- College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul, 151-742, South Korea
| | - Ji Young Chai
- Departments of Rheumatology, Bundang Jesaeng Hospital, Seongnam, 463-774, South Korea
| | - Byeong Chun Lee
- College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul, 151-742, South Korea.
| | - Se Chang Park
- College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul, 151-742, South Korea.
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Kämpf MM, Braun M, Sirena D, Ihssen J, Thöny-Meyer L, Ren Q. In vivo production of a novel glycoconjugate vaccine against Shigella flexneri 2a in recombinant Escherichia coli: identification of stimulating factors for in vivo glycosylation. Microb Cell Fact 2015; 14:12. [PMID: 25612741 PMCID: PMC4308876 DOI: 10.1186/s12934-015-0195-7] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2014] [Accepted: 01/12/2015] [Indexed: 11/26/2022] Open
Abstract
Background Glycoconjugated vaccines composed of polysaccharide antigens covalently linked to immunogenic carrier proteins have proved to belong to the most effective and safest vaccines for combating bacterial pathogens. The functional transfer of the N-glycosylation machinery from Campylobacter jejuni to the standard prokaryotic host Escherichia coli established a novel bioconjugation methodology termed bacterial glycoengineering. Results In this study, we report on the production of a new recombinant glycoconjugate vaccine against Shigella flexneri 2a representing the major serotype for global outbreaks of shigellosis. We demonstrate that S. flexneri 2a O-polysaccharides can be transferred to a detoxified variant of Pseudomonas aeruginosa carrier protein exotoxin A (EPA) by the C. jejuni oligosaccharyltransferase PglB, resulting in glycosylated EPA-2a. Moreover, we optimized the in vivo production of this novel vaccine by identification and quantitative analysis of critical process parameters for glycoprotein synthesis. It was found that sequential induction of oligosaccharyltransferase PglB and carrier protein EPA increased the specific productivity of EPA-2a by a factor of 1.6. Furthermore, by the addition of 10 g/L of the monosaccharide N-acetylglucosamine during induction, glycoconjugate vaccine yield was boosted up to 3.1-fold. The optimum concentration of Mg2+ ions for N-glycan transfer was determined to be 10 mM. Finally, optimized parameters were transferred to high cell density cultures with a 46-fold increase of overall yield of glycoconjugate compared to the one in initial shake flask production. Conclusion The present study is the first attempt to identify stimulating parameters for improved productivity of S. flexneri 2a bioconjugates. Optimization of glycosylation efficiency will ultimately foster the transfer of lab-scale expression to a cost-effective in vivo production process for a glycoconjugate vaccine against S. flexneri 2a in E. coli. This study is an important step towards this goal and provides a starting point for further optimization studies.
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Affiliation(s)
- Michael M Kämpf
- Laboratory for Biointerfaces, Swiss Federal Laboratories for Materials Science and Technology (Empa), Lerchenfeldstrasse 5, CH-9014, St. Gallen, Switzerland. .,GlycoVaxyn AG, Grabenstrasse 3, 8952, Schlieren, Switzerland.
| | - Martin Braun
- GlycoVaxyn AG, Grabenstrasse 3, 8952, Schlieren, Switzerland.
| | | | - Julian Ihssen
- Laboratory for Biointerfaces, Swiss Federal Laboratories for Materials Science and Technology (Empa), Lerchenfeldstrasse 5, CH-9014, St. Gallen, Switzerland.
| | - Linda Thöny-Meyer
- Laboratory for Biointerfaces, Swiss Federal Laboratories for Materials Science and Technology (Empa), Lerchenfeldstrasse 5, CH-9014, St. Gallen, Switzerland.
| | - Qun Ren
- Laboratory for Biointerfaces, Swiss Federal Laboratories for Materials Science and Technology (Empa), Lerchenfeldstrasse 5, CH-9014, St. Gallen, Switzerland.
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9
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Oral administration of live Shigella vaccine candidates in rhesus monkeys show no evidence of competition for colonization and immunogenicity between different serotypes. Vaccine 2014; 32:1754-60. [DOI: 10.1016/j.vaccine.2013.12.068] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2013] [Revised: 11/04/2013] [Accepted: 12/05/2013] [Indexed: 11/15/2022]
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Characterization of a novel fusion protein from IpaB and IpaD of Shigella spp. and its potential as a pan-Shigella vaccine. Infect Immun 2013; 81:4470-7. [PMID: 24060976 DOI: 10.1128/iai.00859-13] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Shigellosis is an important disease in the developing world, where about 90 million people become infected with Shigella spp. each year. We previously demonstrated that the type three secretion apparatus (T3SA) proteins IpaB and IpaD are protective antigens in the mouse lethal pulmonary model. In order to simplify vaccine formulation and process development, we have evaluated a vaccine design that incorporates both of these previously tested Shigella antigens into a single polypeptide chain. To determine if this fusion protein (DB fusion) retains the antigenic and protective capacities of IpaB and IpaD, we immunized mice with the DB fusion and compared the immune response to that elicited by the IpaB/IpaD combination vaccine. Purification of the DB fusion required coexpression with IpgC, the IpaB chaperone, and after purification it maintained the highly α-helical characteristics of IpaB and IpaD. The DB fusion also induced comparable immune responses and retained the ability to protect mice against Shigella flexneri and S. sonnei in the lethal pulmonary challenge. It also offered limited protection against S. dysenteriae challenge. Our results show the feasibility of generating a protective Shigella vaccine comprised of the DB fusion.
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Characterization and complete genome sequence of the Shigella bacteriophage pSf-1. Res Microbiol 2013; 164:979-86. [PMID: 24012542 DOI: 10.1016/j.resmic.2013.08.007] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Accepted: 08/27/2013] [Indexed: 11/21/2022]
Abstract
Shigellosis is a global health problem, and Shigella flexneri is the major cause of this disease. In this study, we isolated a virulent Siphoviridae bacteriophage (phage), pSf-1, that infects S. flexneri. This phage was isolated from the Han River in Korea and was found to infect S. flexneri, Shigella boydii, and Shigella sonnei. One-step growth analysis revealed that this phage has a short latent period (10 min) and a large burst size (86.86 PFU/cell), indicating that pSf-1 has good host infectivity and effective lytic activity. The double-stranded DNA genome of pSf-1 is composed of 51,821 bp with a G + C content of 44.02%. The genome encodes 94 putative ORFs, 71 putative promoters, and 60 transcriptional terminator regions. Genome sequence analysis of pSf-1 and comparative analysis with the homologous Shigella phage Shfl1 revealed that there is a high degree of similarity between pSf-1 and Shfl1 in 54 of the 94 ORFs of pSf-1. The results of this investigation indicate that pSf-1 is a novel Shigella phage and that this phage might have potential uses against shigellosis.
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Ashkenazi S, Cohen D. An update on vaccines against Shigella. THERAPEUTIC ADVANCES IN VACCINES 2013; 1:113-23. [PMID: 24757519 PMCID: PMC3967666 DOI: 10.1177/2051013613500428] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Despite intensive research efforts for more than 60 years, utilizing diverse vaccine strategies, a safe and efficacious vaccine against shigellosis is not available yet. We are currently witnessing innovative approaches based on elucidation of the virulence mechanisms of Shigella, understanding the immune response to the pathogen and progress in molecular technology for developing Shigella vaccines. It is hoped that these will lead to a licensed effective Shigella vaccine to protect humans against the significant worldwide morbidity and mortality caused by this microorganism.
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Affiliation(s)
- Shai Ashkenazi
- Department of Pediatrics A, Schneider Children's Medical Center, 14 Kaplan Street, Petach Tikva 49202, Israel
| | - Dani Cohen
- School of Public Health, Sackler Faculty of Medicine, Tel Aviv University, Israel
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Barandun LJ, Immekus F, Kohler PC, Ritschel T, Heine A, Orlando P, Klebe G, Diederich F. High-affinity inhibitors ofZymomonas mobilistRNA–guanine transglycosylase through convergent optimization. ACTA CRYSTALLOGRAPHICA SECTION D: BIOLOGICAL CRYSTALLOGRAPHY 2013; 69:1798-807. [DOI: 10.1107/s0907444913014509] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Accepted: 05/26/2013] [Indexed: 11/11/2022]
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Bergmann-Leitner ES, Hosie H, Trichilo J, Deriso E, Ranallo RT, Alefantis T, Savranskaya T, Grewal P, Ockenhouse CF, Venkatesan MM, Delvecchio VG, Angov E. Self-adjuvanting bacterial vectors expressing pre-erythrocytic antigens induce sterile protection against malaria. Front Immunol 2013; 4:176. [PMID: 23847617 PMCID: PMC3701146 DOI: 10.3389/fimmu.2013.00176] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2013] [Accepted: 06/18/2013] [Indexed: 11/24/2022] Open
Abstract
Genetically inactivated, Gram-negative bacteria that express malaria vaccine candidates represent a promising novel self-adjuvanting vaccine approach. Antigens expressed on particulate bacterial carriers not only target directly to antigen-presenting cells but also provide a strong danger signal thus circumventing the requirement for potent extraneous adjuvants. E. coli expressing malarial antigens resulted in the induction of either Th1 or Th2 biased responses that were dependent on both antigen and sub-cellular localization. Some of these constructs induced higher quality humoral responses compared to recombinant protein and most importantly they were able to induce sterile protection against sporozoite challenge in a murine model of malaria. In light of these encouraging results, two major Plasmodium falciparum pre-erythrocytic malaria vaccine targets, the Cell-Traversal protein for Ookinetes and Sporozoites (CelTOS) fused to the Maltose-binding protein in the periplasmic space and the Circumsporozoite Protein (CSP) fused to the Outer membrane (OM) protein A in the OM were expressed in a clinically relevant, attenuated Shigella strain (Shigella flexneri 2a). This type of live-attenuated vector has previously undergone clinical investigations as a vaccine against shigellosis. Using this novel delivery platform for malaria, we find that vaccination with the whole-organism represents an effective vaccination alternative that induces protective efficacy against sporozoite challenge. Shigella GeMI-Vax expressing malaria targets warrant further evaluation to determine their full potential as a dual disease, multivalent, self-adjuvanting vaccine system, against both shigellosis, and malaria.
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Abstract
Renewed awareness of the substantial morbidity and mortality that Shigella infection causes among young children in developing countries, combined with technological innovations in vaccinology, has led to the development of novel vaccine strategies in the past 5 years. Along with advancement of classic vaccines in clinical trials and new sophisticated measurements of immunological responses, much new data has been produced, lending promise to the potential for production of safe and effective Shigella vaccines. Herein, we review the latest progress in Shigella vaccine development within the framework of persistent obstacles.
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