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Sears KT, Galen JE, Tennant SM. Advances in the development of Salmonella-based vaccine strategies for protection against Salmonellosis in humans. J Appl Microbiol 2021; 131:2640-2658. [PMID: 33665941 PMCID: PMC9292744 DOI: 10.1111/jam.15055] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 02/18/2021] [Accepted: 03/02/2021] [Indexed: 11/29/2022]
Abstract
Salmonella spp. are important human pathogens globally causing millions of cases of typhoid fever and non‐typhoidal salmonellosis annually. There are only a few vaccines licensed for use in humans which all target Salmonella enterica serovar Typhi. Vaccine development is hampered by antigenic diversity between the thousands of serovars capable of causing infection in humans. However, a number of attenuated candidate vaccine strains are currently being developed. As facultative intracellular pathogens with multiple systems for transporting effector proteins to host cells, attenuated Salmonella strains can also serve as ideal tools for the delivery of foreign antigens to create multivalent live carrier vaccines for simultaneous immunization against several unrelated pathogens. Further, the ease with which Salmonella can be genetically modified and the extensive knowledge of the virulence mechanisms of this pathogen means that this bacterium has often served as a model organism to test new approaches. In this review we focus on (1) recent advances in live attenuated Salmonella vaccine development, (2) improvements in expression of foreign antigens in carrier vaccines and (3) adaptation of attenuated strains as sources of purified antigens and vesicles that can be used for subunit and conjugate vaccines or together with attenuated vaccine strains in heterologous prime‐boosting immunization strategies. These advances have led to the development of new vaccines against Salmonella which have or will soon be tested in clinical trials.
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Affiliation(s)
- K T Sears
- Center for Vaccine Development and Global Health, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA
| | - J E Galen
- Center for Vaccine Development and Global Health, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA
| | - S M Tennant
- Center for Vaccine Development and Global Health, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA
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Galen JE, Wahid R, Buskirk AD. Strategies for Enhancement of Live-Attenuated Salmonella-Based Carrier Vaccine Immunogenicity. Vaccines (Basel) 2021; 9:162. [PMID: 33671124 PMCID: PMC7923097 DOI: 10.3390/vaccines9020162] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Revised: 02/11/2021] [Accepted: 02/15/2021] [Indexed: 12/28/2022] Open
Abstract
The use of live-attenuated bacterial vaccines as carriers for the mucosal delivery of foreign antigens to stimulate the mucosal immune system was first proposed over three decades ago. This novel strategy aimed to induce immunity against at least two distinct pathogens using a single bivalent carrier vaccine. It was first tested using a live-attenuated Salmonella enterica serovar Typhi strain in clinical trials in 1984, with excellent humoral immune responses against the carrier strain but only modest responses elicited against the foreign antigen. Since then, clinical trials with additional Salmonella-based carrier vaccines have been conducted. As with the original trial, only modest foreign antigen-specific immunity was achieved in most cases, despite the incorporation of incremental improvements in antigen expression technologies and carrier design over the years. In this review, we will attempt to deconstruct carrier vaccine immunogenicity in humans by examining the basis of bacterial immunity in the human gastrointestinal tract and how the gut detects and responds to pathogens versus benign commensal organisms. Carrier vaccine design will then be explored to determine the feasibility of retaining as many characteristics of a pathogen as possible to elicit robust carrier and foreign antigen-specific immunity, while avoiding over-stimulation of unacceptably reactogenic inflammatory responses.
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Affiliation(s)
- James E. Galen
- Center for Vaccine Development and Global Health, University of Maryland School of Medicine, Baltimore, MD 21201, USA;
| | - Rezwanul Wahid
- Center for Vaccine Development and Global Health, University of Maryland School of Medicine, Baltimore, MD 21201, USA;
| | - Amanda D. Buskirk
- Center for Drug Evaluation and Research, Office of Pharmaceutical Quality, Office of Process and Facilities, Division of Microbiology Assessment II, U.S. Food and Drug Administration, Silver Spring, MD 20903, USA;
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Salerno-Gonçalves R, Galen JE, Levine MM, Fasano A, Sztein MB. Manipulation of Salmonella Typhi Gene Expression Impacts Innate Cell Responses in the Human Intestinal Mucosa. Front Immunol 2018; 9:2543. [PMID: 30443257 PMCID: PMC6221971 DOI: 10.3389/fimmu.2018.02543] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2018] [Accepted: 10/16/2018] [Indexed: 12/19/2022] Open
Abstract
Although immunity induced by typhoid fever is moderated and short-lived, typhoid vaccination with the attenuated Ty21a oral vaccine generates long-lasting protection rates reaching up to 92%. Thus, there are important differences on how wild-type Salmonella and typhoid vaccine strains stimulate host immunity. We hypothesize that vaccine strains with different mutations might affect gut inflammation and intestinal permeability by different mechanisms. To test this hypothesis, we used an in vitro organotypic model of the human intestinal mucosa composed of human intestinal epithelial cells, lymphocytes/monocytes, endothelial cells, and fibroblasts. We also used six Salmonella enterica serovar Typhi (S. Typhi) strains: the licensed Ty21a oral vaccine, four typhoid vaccine candidates (i.e., CVD 908, CVD 909, CVD 910, and CVD 915) and the wild-type Ty2 strain. We found that genetically engineered S. Typhi vaccine strains elicit differential host changes not only in the intestinal permeability and secretion of inflammatory cytokines, but also in the phenotype and activation pathways of innate cells. These changes were distinct from those elicited by the parent wild-type S. Typhi and depended on the genetic manipulation. In sum, these results emphasize the importance of carefully selecting specific manipulations of the Salmonella genome in the development of typhoid vaccines.
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Affiliation(s)
- Rosângela Salerno-Gonçalves
- Center for Vaccine Development and Global Health, University of Maryland School of Medicine, Baltimore, MD, United States
| | - James E. Galen
- Center for Vaccine Development and Global Health, University of Maryland School of Medicine, Baltimore, MD, United States
| | - Myron M. Levine
- Center for Vaccine Development and Global Health, University of Maryland School of Medicine, Baltimore, MD, United States
| | - Alessio Fasano
- Mucosal Immunology and Biology Research Center, Massachusetts General Hospital for Children, Boston, MA, United States
| | - Marcelo B. Sztein
- Center for Vaccine Development and Global Health, University of Maryland School of Medicine, Baltimore, MD, United States
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Hegerle N, Bose J, Ramachandran G, Galen JE, Levine MM, Simon R, Tennant SM. Overexpression of O-polysaccharide chain length regulators in Gram-negative bacteria using the Wzx-/Wzy-dependent pathway enhances production of defined modal length O-polysaccharide polymers for use as haptens in glycoconjugate vaccines. J Appl Microbiol 2018; 125:575-585. [PMID: 29603538 PMCID: PMC6726474 DOI: 10.1111/jam.13772] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Revised: 10/20/2017] [Accepted: 03/26/2018] [Indexed: 11/30/2022]
Abstract
Aims O‐polysaccharide (OPS) molecules are protective antigens for several bacterial pathogens, and have broad utility as components of glycoconjugate vaccines. Variability in the OPS chain length is one obstacle towards further development of these vaccines. Introduction of sizing steps during purification of OPS molecules of suboptimal or of mixed lengths introduces additional costs and complexity while decreasing the final yield. The overall goal of this study was to demonstrate the utility of engineering Gram‐negative bacteria to produce homogenous O‐polysaccharide populations that can be used as the basis of carbohydrate vaccines by overexpressing O‐polysaccharide chain length regulators of the Wzx‐/Wzy‐dependent pathway. Method and Results The O‐polysaccharide chain length regulators wzzB and fepE from Salmonella Typhimurium I77 and wzz2 from Pseudomonas aeruginosa PAO1 were cloned and expressed in the homologous organism or in other Gram‐negative bacteria. Overexpression of these Wzz proteins in the homologous organism significantly increased the proportion of long or very long chain O‐polysaccharides. The same observation was made when wzzB was overexpressed in Salmonella Paratyphi A and Shigella flexneri, and wzz2 was overexpressed in two other strains of P. aeruginosa. Conclusions Overexpression of Wzz proteins in Gram‐negative bacteria using the Wzx/Wzy‐dependant pathway for lipopolysaccharide synthesis provides a genetic method to increase the production of an O‐polysaccharide population of a defined size. Significance and Impact of the Study The methods presented herein represent a cost‐effective and improved strategy for isolating preferred OPS vaccine haptens, and could facilitate the further use of O‐polysaccharides in glycoconjugate vaccine development.
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Affiliation(s)
- N Hegerle
- Center for Vaccine Development and Institute for Global Health, University of Maryland School of Medicine, Baltimore, MD, USA.,Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA
| | - J Bose
- Center for Vaccine Development and Institute for Global Health, University of Maryland School of Medicine, Baltimore, MD, USA.,Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA
| | - G Ramachandran
- Center for Vaccine Development and Institute for Global Health, University of Maryland School of Medicine, Baltimore, MD, USA.,Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA
| | - J E Galen
- Center for Vaccine Development and Institute for Global Health, University of Maryland School of Medicine, Baltimore, MD, USA.,Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA
| | - M M Levine
- Center for Vaccine Development and Institute for Global Health, University of Maryland School of Medicine, Baltimore, MD, USA.,Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA.,Department of Pediatrics, University of Maryland School of Medicine, Baltimore, MD, USA
| | - R Simon
- Center for Vaccine Development and Institute for Global Health, University of Maryland School of Medicine, Baltimore, MD, USA.,Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA
| | - S M Tennant
- Center for Vaccine Development and Institute for Global Health, University of Maryland School of Medicine, Baltimore, MD, USA.,Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA
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Galen JE, Buskirk AD, Tennant SM, Pasetti MF. Live Attenuated Human Salmonella Vaccine Candidates: Tracking the Pathogen in Natural Infection and Stimulation of Host Immunity. EcoSal Plus 2016; 7:10.1128/ecosalplus.ESP-0010-2016. [PMID: 27809955 PMCID: PMC5119766 DOI: 10.1128/ecosalplus.esp-0010-2016] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/08/2023]
Abstract
Salmonellosis, caused by members of the genus Salmonella, is responsible for considerable global morbidity and mortality in both animals and humans. In this review, we will discuss the pathogenesis of Salmonella enterica serovar Typhi and Salmonella enterica serovar Typhimurium, focusing on human Salmonella infections. We will trace the path of Salmonella through the body, including host entry sites, tissues and organs affected, and mechanisms involved in both pathogenesis and stimulation of host immunity. Careful consideration of the natural progression of disease provides an important context in which attenuated live oral vaccines can be rationally designed and developed. With this in mind, we will describe a series of attenuated live oral vaccines that have been successfully tested in clinical trials and demonstrated to be both safe and highly immunogenic. The attenuation strategies summarized in this review offer important insights into further development of attenuated vaccines against other Salmonella for which live oral candidates are currently unavailable.
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Affiliation(s)
- James E. Galen
- Center for Vaccine Development, Institute for Global Health, University of Maryland School of Medicine, Baltimore MD 21201
- Division of Geographic Medicine, Department of Medicine, University of Maryland School of Medicine, Baltimore MD 21201
- Corresponding author: James E. Galen,
| | - Amanda D. Buskirk
- Center for Vaccine Development, Institute for Global Health, University of Maryland School of Medicine, Baltimore MD 21201
- Division of Infectious Diseases and Tropical Pediatrics, Department of Pediatrics, University of Maryland School of Medicine, Baltimore MD 21201
| | - Sharon M. Tennant
- Center for Vaccine Development, Institute for Global Health, University of Maryland School of Medicine, Baltimore MD 21201
- Division of Geographic Medicine, Department of Medicine, University of Maryland School of Medicine, Baltimore MD 21201
| | - Marcela F. Pasetti
- Center for Vaccine Development, Institute for Global Health, University of Maryland School of Medicine, Baltimore MD 21201
- Division of Infectious Diseases and Tropical Pediatrics, Department of Pediatrics, University of Maryland School of Medicine, Baltimore MD 21201
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Higginson EE, Galen JE, Levine MM, Tennant SM. Microgravity as a biological tool to examine host-pathogen interactions and to guide development of therapeutics and preventatives that target pathogenic bacteria. Pathog Dis 2016; 74:ftw095. [PMID: 27630185 DOI: 10.1093/femspd/ftw095] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/31/2016] [Indexed: 12/16/2022] Open
Abstract
Space exploration programs have long been interested in the effects of spaceflight on biology. This research is important not only in its relevance to future deep space exploration, but also because it has allowed investigators to ask questions about how gravity impacts cell behavior here on Earth. In the 1980s, scientists designed and built the first rotating wall vessel, capable of mimicking the low shear environment found in space. This vessel has since been used to investigate growth of both microorganisms and human tissue cells in low shear modeled microgravity conditions. Bacterial behavior has been shown to be altered both in space and under simulated microgravity conditions. In some cases, bacteria appear attenuated, whereas in others virulence is enhanced. This has consequences not only for manned spaceflight, but poses larger questions about the ability of bacteria to sense the world around them. By using the microgravity environment as a tool, we can exploit this phenomenon in the search for new therapeutics and preventatives against pathogenic bacteria for use both in space and on Earth.
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Affiliation(s)
- Ellen E Higginson
- Center for Vaccine Development and Institute for Global Health, University of Maryland School of Medicine, Baltimore, MD 21201, USA Department of Medicine, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - James E Galen
- Center for Vaccine Development and Institute for Global Health, University of Maryland School of Medicine, Baltimore, MD 21201, USA Department of Medicine, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Myron M Levine
- Center for Vaccine Development and Institute for Global Health, University of Maryland School of Medicine, Baltimore, MD 21201, USA Department of Medicine, University of Maryland School of Medicine, Baltimore, MD 21201, USA Department of Pediatrics, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Sharon M Tennant
- Center for Vaccine Development and Institute for Global Health, University of Maryland School of Medicine, Baltimore, MD 21201, USA Department of Medicine, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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Xu X, Wood MS, Kurbanov S, Guo L, Gao X, Galen JE, Metelitsa LS. 191. Development of an Effective Cancer Vaccine Platform Using Attenuated Salmonella to Deliver Recombinant Tumor-Associated Antigens. Mol Ther 2016. [DOI: 10.1016/s1525-0016(16)33000-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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8
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Xu X, Kurbanov S, Guo L, Gao X, Galen JE, Metelitsa LS. 217. Development of an Effective Cancer Vaccine Platform Using Attenuated Salmonella to Deliver Recombinant Tumor-Associated Antigens. Mol Ther 2015. [DOI: 10.1016/s1525-0016(16)33822-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
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9
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Boyd MA, Tennant SM, Melendez JH, Toema D, Galen JE, Geddes CD, Levine MM. Adaptation of red blood cell lysis represents a fundamental breakthrough that improves the sensitivity of Salmonella detection in blood. J Appl Microbiol 2015; 118:1199-209. [PMID: 25630831 PMCID: PMC4418380 DOI: 10.1111/jam.12769] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Revised: 01/20/2015] [Accepted: 01/22/2015] [Indexed: 11/29/2022]
Abstract
AIMS Isolation of Salmonella Typhi from blood culture is the standard diagnostic for confirming typhoid fever but it is unavailable in many developing countries. We previously described a Microwave Accelerated Metal Enhanced Fluorescence (MAMEF)-based assay to detect Salmonella in medium. Attempts to detect Salmonella in blood were unsuccessful, presumably due to the interference of erythrocytes. The objective of this study was to evaluate various blood treatment methods that could be used prior to PCR, real-time PCR or MAMEF to increase sensitivity of detection of Salmonella. METHODS AND RESULTS We tested ammonium chloride and erythrocyte lysis buffer, water, Lymphocyte Separation Medium, BD Vacutainer(®) CPT(™) Tubes and dextran. Erythrocyte lysis buffer was the best isolation method as it is fast, inexpensive and works with either fresh or stored blood. The sensitivity of PCR- and real-time PCR detection of Salmonella in spiked blood was improved when whole blood was first lysed using erythrocyte lysis buffer prior to DNA extraction. Removal of erythrocytes and clotting factors also enabled reproducible lysis of Salmonella and fragmentation of DNA, which are necessary for MAMEF sensing. CONCLUSIONS Use of the erythrocyte lysis procedure prior to DNA extraction has enabled improved sensitivity of Salmonella detection by PCR and real-time PCR and has allowed lysis and fragmentation of Salmonella using microwave radiation (for future detection by MAMEF). SIGNIFICANCE AND IMPACT OF THE STUDY Adaptation of the blood lysis method represents a fundamental breakthrough that improves the sensitivity of DNA-based detection of Salmonella in blood.
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Affiliation(s)
- M A Boyd
- Center for Vaccine Development, University of Maryland Baltimore, Baltimore, MD, USA; Department of Pediatrics, University of Maryland Baltimore, Baltimore, MD, USA
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10
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Abstract
Contemporary vaccine development relies less on empirical methods of vaccine construction, and now employs a powerful array of precise engineering strategies to construct immunogenic live vaccines. In this review, we will survey various engineering techniques used to create attenuated vaccines, with an emphasis on recent advances and insights. We will further explore the adaptation of attenuated strains to create multivalent vaccine platforms for immunization against multiple unrelated pathogens. These carrier vaccines are engineered to deliver sufficient levels of protective antigens to appropriate lymphoid inductive sites to elicit both carrier-specific and foreign antigen-specific immunity. Although many of these technologies were originally developed for use in Salmonella vaccines, application of the essential logic of these approaches will be extended to development of other enteric vaccines where possible. A central theme driving our discussion will stress that the ultimate success of an engineered vaccine rests on achieving the proper balance between attenuation and immunogenicity. Achieving this balance will avoid over-activation of inflammatory responses, which results in unacceptable reactogenicity, but will retain sufficient metabolic fitness to enable the live vaccine to reach deep tissue inductive sites and trigger protective immunity. The breadth of examples presented herein will clearly demonstrate that genetic engineering offers the potential for rapidly propelling vaccine development forward into novel applications and therapies which will significantly expand the role of vaccines in public health.
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Affiliation(s)
- James E Galen
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, MD 21201, USA; Division of Geographic Medicine, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
| | - Roy Curtiss
- Center for Infectious Diseases and Vaccinology, The Biodesign Institute and School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA
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Simon R, Wang JY, Boyd MA, Tulapurkar ME, Ramachandran G, Tennant SM, Pasetti M, Galen JE, Levine MM. Sustained protection in mice immunized with fractional doses of Salmonella Enteritidis core and O polysaccharide-flagellin glycoconjugates. PLoS One 2013; 8:e64680. [PMID: 23741368 PMCID: PMC3669428 DOI: 10.1371/journal.pone.0064680] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2013] [Accepted: 04/17/2013] [Indexed: 11/26/2022] Open
Abstract
Non-typhoidal Salmonella (NTS) serovars S. Enteritidis and S. Typhimurium are a major cause of invasive bacterial disease (e.g., bacteremia, meningitis) in infants and young children in sub-Saharan Africa and also occasionally cause invasive disease in highly susceptible hosts (young infants, the elderly, and immunocompromised subjects) in industrialized countries. No licensed vaccines exist against human NTS infections. NTS core and O polysaccharide (COPS) and FliC (Phase 1 flagellin subunits) each constitute protective antigens in murine models. S. Enteritidis COPS conjugated to FliC represents a promising vaccine approach that elicits binding and opsonophagocytic antibodies and protects mice against lethal challenge with virulent S. Enteritidis. We examined the protective efficacy of fractional dosages of S. Enteritidis COPS:FliC conjugate vaccines in mice, and also established that protection can be passively transferred to naïve mice by administering sera from mice immunized with conjugate. Mice were immunized with three doses of either 10 µg, 2.5 µg (full dose), 0.25 µg, or 0.025 µg S. Enteritidis COPS:FliC conjugate at 28 day intervals. Antibody titers to COPS and FliC measured by ELISA fell consonant with progressively smaller vaccine dosage levels; anti-FliC IgG responses remained robust at fractional dosages for which anti-COPS serum IgG titers were decreased. Nevertheless, >90% protection against intraperitoneal challenge was observed in mice immunized with fractional dosages of conjugate that elicited diminished titers to both FliC and COPS. Passive transfer of immune sera from mice immunized with the highest dose of COPS:FliC to naïve mice was also protective, demonstrating the role of antibodies in mediating protection. These results provide important insights regarding the potency of Salmonella glycoconjugate vaccines that use flagellin as a carrier protein.
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Affiliation(s)
- Raphael Simon
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.
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12
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Abstract
Bacterial live vector vaccines represent a vaccine development strategy that offers exceptional flexibility. In this approach, genes encoding protective antigens of unrelated bacterial, viral or parasitic pathogens are expressed in an attenuated bacterial vaccine strain that delivers these foreign antigens to the immune system, thereby eliciting relevant immune responses. Rather than expressing these antigens using low copy expression plasmids, here we pursue expression of foreign proteins from the live vector chromosome. Our strategy is designed to compensate for the inherent disadvantage of loss of gene dosage (vs. plasmid-based expression) by integrating antigen-encoding gene cassettes into multiple chromosomal sites already inactivated in an attenuated Salmonella enterica serovar Typhi vaccine candidate. We tested expression of a cassette encoding the green fluorescent protein (GFPuv) integrated separately into native guaBA, htrA or clyA chromosomal loci. Using single integrations, we show that expression levels of GFPuv are significantly affected by the site of integration, regardless of the inclusion of additional strong promoters within the incoming cassette. Using cassettes integrated into both guaBA and htrA, we observe cumulative synthesis levels from two integration sites superior to single integrations. Most importantly, we observe that GFPuv expression increases in a growth phase-dependent manner, suggesting that foreign antigen synthesis may be “tuned” to the physiology of the live vaccine. We expect this novel platform expression technology to prove invaluable in the development of a wide variety of multivalent live vector vaccines, capable of expressing multiple antigens from both chromosomal and plasmid-based expression systems within a single strain.
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Affiliation(s)
- Jin Yuan Wang
- Center for Vaccine Development; Division of Geographic Medicine; Baltimore, MD USA; Department of Medicine; University of Maryland School of Medicine; Baltimore, MD USA
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13
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Mellado-Sanchez G, Ramirez K, Drachenberg CB, Diaz-McNair J, Rodriguez AL, Galen JE, Nataro JP, Pasetti MF. Characterization of systemic and pneumonic murine models of plague infection using a conditionally virulent strain. Comp Immunol Microbiol Infect Dis 2012. [PMID: 23195858 DOI: 10.1016/j.cimid.2012.10.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Yersinia pestis causes bubonic and pneumonic plague in humans. The pneumonic infection is the most severe and invariably fatal if untreated. Because of its high virulence, ease of delivery and precedent of use in warfare, Y. pestis is considered as a potential bioterror agent. No licensed plague vaccine is currently available in the US. Laboratory research with virulent strains requires appropriate biocontainment (i.e., Biosafety Level 3 (BSL-3) for procedures that generate aerosol/droplets) and secure facilities that comply with federal select agent regulations. To assist in the identification of promising vaccine candidates during the early phases of development, we characterized mouse models of systemic and pneumonic plague infection using the Y. pestis strain EV76, an attenuated human vaccine strain that can be rendered virulent in mice under in vivo iron supplementation. Mice inoculated intranasally or intravenously with Y. pestis EV76 in the presence of iron developed a systemic and pneumonic plague infection that resulted in disease and lethality. Bacteria replicated and severely compromised the spleen, liver and lungs. Susceptibility was age dependent, with younger mice being more vulnerable to pneumonic infection. We used these models of infection to assess the protective capacity of newly developed Salmonella-based plague vaccines. The protective outcome varied depending on the route and dose of infection. Protection was associated with the induction of specific immunological effectors in systemic/mucosal compartments. The models of infection described could serve as safe and practical tools for identifying promising vaccine candidates that warrant further potency evaluation using fully virulent strains in BSL-3 settings.
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Affiliation(s)
- Gabriela Mellado-Sanchez
- Department of Pediatrics, Center for Vaccine Development, University of Maryland School of Medicine, 685 West Baltimore St., Room 480, Baltimore, MD 21201, USA
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Galen JE, Simon R, Ernst RK. Salmonella expressing detoxified lipopolysaccharide is immunogenic and protective both as an attenuated vaccine and for delivery of foreign antigens. Expert Rev Vaccines 2012; 10:1679-82. [PMID: 22085171 DOI: 10.1586/erv.11.155] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The construction of safe and protective vaccines, derived from human pathogens that have been genetically modified to remove pathogenicity, is often easier to accomplish on paper than it is in the laboratory. Kong and colleagues have pursued a clever strategy to reduce the reactogenicity of attenuated Salmonella oral vaccines by genetically modifying the surface lipopolysaccharide to lower endotoxic activity. The resulting candidate vaccine strains were highly reduced in virulence yet were able to confer protection in a mouse model against challenge with virulent Salmonella. Remarkably, these strains could also be further modified to present foreign antigens from unrelated human pathogens and again confer protection against heterologous challenge. This work brings important new tools to bear on solving the problem of creating efficacious attenuated bacterial vaccines that maximize both safety and immunogenicity in clinical trials.
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Affiliation(s)
- James E Galen
- Center for Vaccine Development, University of Maryland, Baltimore, MD 21201, USA.
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15
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Gat O, Galen JE, Tennant S, Simon R, Blackwelder WC, Silverman DJ, Pasetti MF, Levine MM. Cell-associated flagella enhance the protection conferred by mucosally-administered attenuated Salmonella Paratyphi A vaccines. PLoS Negl Trop Dis 2011; 5:e1373. [PMID: 22069504 PMCID: PMC3206010 DOI: 10.1371/journal.pntd.0001373] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Accepted: 09/08/2011] [Indexed: 11/25/2022] Open
Abstract
BACKGROUND Antibiotic-resistant Salmonella enterica serovar Paratyphi A, the agent of paratyphoid A fever, poses an emerging public health dilemma in endemic areas of Asia and among travelers, as there is no licensed vaccine. Integral to our efforts to develop a S. Paratyphi A vaccine, we addressed the role of flagella as a potential protective antigen by comparing cell-associated flagella with exported flagellin subunits expressed by attenuated strains. METHODOLOGY S. Paratyphi A strain ATCC 9150 was first deleted for the chromosomal guaBA locus, creating CVD 1901. Further chromosomal deletions in fliD (CVD 1901D) or flgK (CVD 1901K) were then engineered, resulting in the export of unpolymerized FliC, without impairing its overall expression. The virulence of the resulting isogenic strains was examined using a novel mouse LD(50) model to accommodate the human-host restricted S. Paratyphi A. The immunogenicity of the attenuated strains was then tested using a mouse intranasal model, followed by intraperitoneal challenge with wildtype ATCC 9150. RESULTS Mucosal (intranasal) immunization of mice with strain CVD 1901 expressing cell-associated flagella conferred superior protection (vaccine efficacy [VE], 90%) against a lethal intraperitoneal challenge, compared with the flagellin monomer-exporting mutants CVD 1901K (30% VE) or CVD 1901D (47% VE). The superior protection induced by CVD 1901 with its cell-attached flagella was associated with an increased IgG2a:IgG1 ratio of FliC-specific antibodies with enhanced opsonophagocytic capacity. CONCLUSIONS Our results clearly suggest that enhanced anti-FliC antibody-mediated clearance of S. Paratyphi A by phagocytic cells, induced by vaccines expressing cell-associated rather than exported FliC, might be contributing to the vaccine-induced protection from S. Paratyphi A challenge in vivo. We speculate that an excess of IgG1 anti-FliC antibodies induced by the exported FliC may compete with the IgG2a subtype and block binding to specific phagocyte Fc receptors that are critical for clearing an S. Paratyphi A infection.
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Affiliation(s)
- Orit Gat
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - James E. Galen
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - Sharon Tennant
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - Raphael Simon
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - William C. Blackwelder
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - David J. Silverman
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - Marcela F. Pasetti
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Department of Pediatrics, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - Myron M. Levine
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Department of Pediatrics, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
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16
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Simon R, Tennant SM, Galen JE, Levine MM. Mouse models to assess the efficacy of non-typhoidal Salmonella vaccines: revisiting the role of host innate susceptibility and routes of challenge. Vaccine 2011; 29:5094-106. [PMID: 21616112 DOI: 10.1016/j.vaccine.2011.05.022] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2011] [Revised: 04/22/2011] [Accepted: 05/09/2011] [Indexed: 01/24/2023]
Abstract
Non-typhoidal Salmonella enterica (NTS) serovars Typhimurium and Enteritidis are important causes of bacterial gastroenteritis in the USA and worldwide. In sub-Saharan Africa these two serovars are emerging as agents associated with lethal invasive disease (e.g., bacteremia, meningitis). The development of NTS vaccines, based on mucosally administered live attenuated strains and parenteral non-living antigens, could diminish the NTS disease burden globally. Mouse models of S. Typhimurium and S. Enteritidis invasive disease can accelerate the development of NTS vaccines. Live attenuated NTS vaccines elicit both cellular and humoral immunity in mice and their efficacy is well established. In contrast, non-living vaccines that primarily elicit humoral immunity have demonstrated variable efficacy. An analysis of the reported studies with non-living vaccines against S. Typhimurium and S. Enteritidis reveals that efficacy is influenced by two important independent variables: (1) the innate susceptibility to NTS infection that differs dramatically between commonly used mouse strains and (2) the virulence of the NTS strain used for challenge. Protection by non-living vaccines has generally been seen only in host-pathogen interactions where a sub-lethal infection results, such as challenging resistant mice with either highly virulent or weakly virulent strains or susceptible mice with weakly virulent strains. The immunologic basis of this discrepancy and the implications for human NTS vaccine development are reviewed herein.
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Affiliation(s)
- Raphael Simon
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, MD, 21201, USA.
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17
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Tennant SM, Zhang Y, Galen JE, Geddes CD, Levine MM. Ultra-fast and sensitive detection of non-typhoidal Salmonella using microwave-accelerated metal-enhanced fluorescence ("MAMEF"). PLoS One 2011; 6:e18700. [PMID: 21494634 PMCID: PMC3073000 DOI: 10.1371/journal.pone.0018700] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Accepted: 03/08/2011] [Indexed: 01/11/2023] Open
Abstract
Certain serovars of Salmonella enterica subsp. enterica cause invasive disease (e.g., enteric fever, bacteremia, septicemia, meningitis, etc.) in humans and constitute a global public health problem. A rapid, sensitive diagnostic test is needed to allow prompt initiation of therapy in individual patients and for measuring disease burden at the population level. An innovative and promising new rapid diagnostic technique is microwave-accelerated metal-enhanced fluorescence (MAMEF). We have adapted this assay platform to detect the chromosomal oriC locus common to all Salmonella enterica subsp. enterica serovars. We have shown efficient lysis of biologically relevant concentrations of Salmonella spp. suspended in bacteriological media using microwave-induced lysis. Following lysis and DNA release, as little as 1 CFU of Salmonella in 1 ml of medium can be detected in <30 seconds. Furthermore the assay is sensitive and specific: it can detect oriC from Salmonella serovars Typhi, Paratyphi A, Paratyphi B, Paratyphi C, Typhimurium, Enteritidis and Choleraesuis but does not detect Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Streptococcus pneumoniae, Haemophilus influenzae or Acinetobacter baumanii. We have also performed preliminary experiments using a synthetic Salmonella oriC oligonucleotide suspended in whole human blood and observed rapid detection when the sample was diluted 1∶1 with PBS. These pre-clinical data encourage progress to the next step to detect Salmonella in blood (and other ordinarily sterile, clinically relevant body fluids).
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Affiliation(s)
- Sharon M Tennant
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.
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18
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Ramirez K, Ditamo Y, Galen JE, Baillie LWJ, Pasetti MF. Mucosal priming of newborn mice with S. Typhi Ty21a expressing anthrax protective antigen (PA) followed by parenteral PA-boost induces B and T cell-mediated immunity that protects against infection bypassing maternal antibodies. Vaccine 2010; 28:6065-75. [PMID: 20619377 DOI: 10.1016/j.vaccine.2010.06.089] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2010] [Revised: 06/20/2010] [Accepted: 06/25/2010] [Indexed: 10/19/2022]
Abstract
The currently licensed anthrax vaccine has several limitations and its efficacy has been proven only in adults. Effective immunization of newborns and infants requires adequate stimulation of their immune system, which is competent but not fully activated. We explored the use of the licensed live attenuated S. Typhi vaccine strain Ty21a expressing Bacillus anthracis protective antigen [Ty21a(PA)] followed PA-alum as a strategy for immunizing the pediatric population. Newborn mice primed with a single dose of Ty21a(PA) exhibited high frequencies of mucosal IgA-secreting B cells and IFN-gamma-secreting T cells during the neonatal period, none of which was detected in newborns immunized with a single dose of PA-alum. Priming with Ty21a(PA) followed by PA-boost resulted in high levels of PA-specific IgG, toxin neutralizing and opsonophagocytic antibodies and increased frequency of bone marrow IgG plasma cells and memory B cells compared with repeated immunization with PA-alum alone. Robust B and T cell responses developed even in the presence of maternal antibodies. The prime-boost protected against systemic and respiratory infection. Mucosal priming with a safe and effective S. Typhi-based anthrax vaccine followed by PA-boost could serve as a practical and effective prophylactic approach to prevent anthrax early in life.
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Affiliation(s)
- Karina Ramirez
- Center for Vaccine Development, Department of Pediatrics, University of Maryland School of Medicine, 685 West Baltimore St. Room 480, Baltimore, MD 21201, USA
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19
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Galen JE, Chinchilla M, Pasetti MF, Wang JY, Zhao L, Arciniega-Martinez I, Silverman DJ, Levine MM. Mucosal immunization with attenuated Salmonella enterica serovar Typhi expressing protective antigen of anthrax toxin (PA83) primes monkeys for accelerated serum antibody responses to parenteral PA83 vaccine. J Infect Dis 2009; 199:326-35. [PMID: 19099487 DOI: 10.1086/596066] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Salmonella enterica serovar Typhi vaccine strain CVD 908-htrA was genetically engineered for stable plasmid-based expression of protective antigen of anthrax toxin (PA83) fused with the export protein ClyA (ClyA-PA83). The priming potential of CVD 908-htrA expressing ClyA-PA83 was assessed in 12 rhesus and 20 cynomolgus macaques that were immunized mucosally (i.e., intranasally) on days 0 and 14. A parenteral booster with purified PA83 plus alum was given to rhesus macaques on days 42 and 225; cynomolgus monkeys received a booster with either PA or licensed anthrax vaccine (BioThrax; Emergent Biosolutions) only one time, 3 months after priming. Monkeys primed with S. Typhi expressing ClyA-PA83 developed high levels of serum toxin-neutralization activity (TNA) antibodies (50% effective dose [ED50], >1.3x10(3)), 7 days after receipt of the booster, whereas unprimed controls lacked serum TNA (ED50, 0). In nonhuman primates, the success of this anthrax vaccine strategy based on heterologous mucosal priming followed by a parenteral subunit vaccine booster paves the way for clinical trials.
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Affiliation(s)
- James E Galen
- Center for Vaccine Development, Division of Geographic Medicine, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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20
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Chinchilla M, Pasetti MF, Medina-Moreno S, Wang JY, Gomez-Duarte OG, Stout R, Levine MM, Galen JE. Enhanced immunity to Plasmodium falciparum circumsporozoite protein (PfCSP) by using Salmonella enterica serovar Typhi expressing PfCSP and a PfCSP-encoding DNA vaccine in a heterologous prime-boost strategy. Infect Immun 2007; 75:3769-79. [PMID: 17502396 PMCID: PMC1951980 DOI: 10.1128/iai.00356-07] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Two Salmonella enterica serovar Typhi strains that express and export a truncated version of Plasmodium falciparum circumsporozoite surface protein (tCSP) fused to Salmonella serovar Typhi cytolysin A (ClyA) were constructed as a first step in the development of a preerythrocytic malaria vaccine. Synthetic codon-optimized genes (t-csp1 and t-csp2), containing immunodominant B- and T-cell epitopes present in native P. falciparum circumsporozoite surface protein (PfCSP), were fused in frame to the carboxyl terminus of the ClyA gene (clyA::t-csp) in genetically stabilized expression plasmids. Expression and export of ClyA-tCSP1 and ClyA-tCSP2 by Salmonella serovar Typhi vaccine strain CVD 908-htrA were demonstrated by immunoblotting of whole-cell lysates and culture supernatants. The immunogenicity of these constructs was evaluated using a "heterologous prime-boost" approach consisting of mucosal priming with Salmonella serovar Typhi expressing ClyA-tCSP1 and ClyA-tCSP2, followed by parenteral boosting with PfCSP DNA vaccines pVR2510 and pVR2571. Mice primed intranasally on days 0 and 28 with CVD 908-htrA(pSEC10tcsp2) and boosted intradermally on day 56 with PfCSP DNA vaccine pVR2571 induced high titers of serum NANP immunoglobulin G (IgG) (predominantly IgG2a); no serological responses to DNA vaccination were observed in the absence of Salmonella serovar Typhi-PfCSP priming. Mice primed with Salmonella serovar Typhi expressing tCSP2 and boosted with PfCSP DNA also developed high frequencies of gamma interferon-secreting cells, which surpassed those produced by PfCSP DNA in the absence of priming. A prime-boost regimen consisting of mucosal delivery of PfCSP exported from a Salmonella-based live-vector vaccine followed by a parenteral PfCSP DNA boosting is a promising strategy for the development of a live-vector-based malaria vaccine.
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Affiliation(s)
- Magaly Chinchilla
- Center for Vaccine Development, University of Maryland, 685 W. Baltimore Street, HSF I, Room 480, Baltimore, MD 21201, USA.
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21
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Stokes MGM, Titball RW, Neeson BN, Galen JE, Walker NJ, Stagg AJ, Jenner DC, Thwaite JE, Nataro JP, Baillie LWJ, Atkins HS. Oral administration of a Salmonella enterica-based vaccine expressing Bacillus anthracis protective antigen confers protection against aerosolized B. anthracis. Infect Immun 2006; 75:1827-34. [PMID: 17145938 PMCID: PMC1865694 DOI: 10.1128/iai.01242-06] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bacillus anthracis is the causative agent of anthrax, a disease that affects wildlife, livestock, and humans. Protection against anthrax is primarily afforded by immunity to the B. anthracis protective antigen (PA), particularly PA domains 4 and 1. To further the development of an orally delivered human vaccine for mass vaccination against anthrax, we produced Salmonella enterica serovar Typhimurium expressing full-length PA, PA domains 1 and 4, or PA domain 4 using codon-optimized PA DNA fused to the S. enterica serovar Typhi ClyA and under the control of the ompC promoter. Oral immunization of A/J mice with Salmonella expressing full-length PA protected five of six mice against a challenge with 10(5) CFU of aerosolized B. anthracis STI spores, whereas Salmonella expressing PA domains 1 and 4 provided only 25% protection (two of eight mice), and Salmonella expressing PA domain 4 or a Salmonella-only control afforded no measurable protection. However, a purified recombinant fusion protein of domains 1 and 4 provided 100% protection, and purified recombinant 4 provided protection in three of eight immunized mice. Thus, we demonstrate for the first time the efficacy of an oral S. enterica-based vaccine against aerosolized B. anthracis spores.
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Affiliation(s)
- Margaret G M Stokes
- Department of Biomedical Sciences, Defence Science and Technology Laboratory, Porton Down, Salisbury, Wiltshire SP4 0JQ, United Kingdom
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22
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Galen JE, Zhao L, Chinchilla M, Wang JY, Pasetti MF, Green J, Levine MM. Adaptation of the endogenous Salmonella enterica serovar Typhi clyA-encoded hemolysin for antigen export enhances the immunogenicity of anthrax protective antigen domain 4 expressed by the attenuated live-vector vaccine strain CVD 908-htrA. Infect Immun 2004; 72:7096-106. [PMID: 15557633 PMCID: PMC529119 DOI: 10.1128/iai.72.12.7096-7106.2004] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bacterial live-vector vaccines aim to deliver foreign antigens to the immune system and induce protective immune responses, and surface-expressed or secreted antigens are generally more immunogenic than cytoplasmic constructs. We hypothesize that an optimum expression system will use an endogenous export system to avoid the need for large amounts of heterologous DNA encoding additional proteins. Here we describe the cryptic chromosomally encoded 34-kDa cytolysin A hemolysin of Salmonella enterica serovar Typhi (ClyA) as a novel export system for the expression of heterologous antigens in the supernatant of attenuated Salmonella serovar Typhi live-vector vaccine strains. We constructed a genetic fusion of ClyA to the reporter green fluorescent protein and showed that in Salmonella serovar Typhi CVD 908-htrA, the fusion protein retains biological activity in both domains and is exported into the supernatant of an exponentially growing live vector in the absence of detectable bacterial lysis. The utility of ClyA for enhancing the immunogenicity of an otherwise problematic antigen was demonstrated by engineering ClyA fused to the domain 4 (D4) moiety of Bacillus anthracis protective antigen (PA). A total of 11 of 15 mice immunized intranasally with Salmonella serovar Typhi exporting the protein fusion manifested fourfold or greater rises in serum anti-PA immunoglobulin G, compared with only 1 of 16 mice immunized with the live vector expressing cytoplasmic D4 (P = 0.0002). In addition, the induction of PA-specific gamma interferon and interleukin 5 responses was observed in splenocytes. This technology offers exceptional versatility for enhancing the immunogenicity of bacterial live-vector vaccines.
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Affiliation(s)
- James E Galen
- Center for Vaccine Development, Separtmrnt of Medicine, School of Medicine, University of Maryland, 685 W. Baltimore St., Baltimore, MD 21201, USA.
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23
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Wyborn NR, Clark A, Roberts RE, Jamieson SJ, Tzokov S, Bullough PA, Stillman TJ, Artymiuk PJ, Galen JE, Zhao L, Levine MM, Green J. Properties of haemolysin E (HlyE) from a pathogenic Escherichia coli avian isolate and studies of HlyE export. Microbiology (Reading) 2004; 150:1495-1505. [PMID: 15133111 DOI: 10.1099/mic.0.26877-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Haemolysin E (HlyE) is a novel pore-forming toxin first identified in Escherichia coli K-12. Analysis of the 3-D structure of HlyE led to the proposal that a unique hydrophobic β-hairpin structure (the β-tongue, residues 177–203) interacts with the lipid bilayer in target membranes. In seeming contradiction to this, the hlyE sequence from a pathogenic E. coli strain (JM4660) that lacks all other haemolysins has been reported to encode an Arg residue at position 188 that was difficult to reconcile with the proposed role of the β-tongue. Here it is shown that the JM4660 hlyE sequence encodes Gly, not Arg, at position 188 and that substitution of Gly188 by Arg in E. coli K-12 HlyE abolishes activity, emphasizing the importance of the head domain in HlyE function. Nevertheless, 76 other amino acid substitutions were confirmed compared to the HlyE protein of E. coli K-12. The JM4660 HlyE protein was dimeric, suggesting a mechanism for improving toxin solubility, and it lysed red blood cells from many species by forming 36–41 Å diameter pores. However, the haemolytic phenotype of JM4660 was found to be unstable due to defects in HlyE export, indicating that export of active HlyE is not an intrinsic property of the protein but requires additional components. TnphoA mutagenesis of hlyE shows that secretion from the cytoplasm to the periplasm does not require the carboxyl-terminal region of HlyE. Finally, disruption of genes associated with cell envelope function, including tatC, impairs HlyE export, indicating that outer membrane integrity is important for effective HlyE secretion.
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Affiliation(s)
- Neil R Wyborn
- Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - Angela Clark
- Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - Ruth E Roberts
- Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - Stuart J Jamieson
- Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - Svetomir Tzokov
- Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - Per A Bullough
- Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - Timothy J Stillman
- Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - Peter J Artymiuk
- Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - James E Galen
- Center for Vaccine Development, Division of Infectious Diseases and Tropical Pediatrics, University of Maryland School of Medicine, 685 W. Baltimore St, Baltimore, MD 21201, USA
| | - Licheng Zhao
- Center for Vaccine Development, Division of Infectious Diseases and Tropical Pediatrics, University of Maryland School of Medicine, 685 W. Baltimore St, Baltimore, MD 21201, USA
| | - Myron M Levine
- Center for Vaccine Development, Division of Infectious Diseases and Tropical Pediatrics, University of Maryland School of Medicine, 685 W. Baltimore St, Baltimore, MD 21201, USA
| | - Jeffrey Green
- Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
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Abstract
There are surprisingly few studies that have successfully used the green fluorescent protein (GFP) as a quantitative reporter in selection experiments screening for inducible bacterial promoters. One explanation is that GFP expression may confer a fitness cost for bacteria. To test this possibility, we monitored the doubling time in enteric bacteria expressing GFP. Four bacterial species, Escherichia coli, enterohaemorrhagic E. coli, Shigella flexneri, Salmonella typhi, and Vibrio cholerae, were examined. The level of GFP expression was varied by using a salt-inducible promoter. After accounting for the increase in doubling time resulting from elevated osmolarity, the doubling time of all bacteria was found to increase proportionally with GFP expression, and some strains were more affected than others. Cultures of the bacteria most affected by GFP exhibited a proportion of elongated cells, which suggests that GFP production could interfere with cell division in these strains. The results in this study show that GFP is costly to bacteria and suggest that overly active promoters should be difficult to obtain from a genomic promoter library. They also suggest that the chances of succeeding in using GFP as a reporter in selection experiments are increased by growing the bacteria for the fewest number of generations and by subduing the expression of GFP whenever possible, such as by using a low copy vector to clone the library.
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Affiliation(s)
- Camilla Rang
- Division of Biology, University of California, San Diego, La Jolla, CA 92093-0116, USA.
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25
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Altboum Z, Levine MM, Galen JE, Barry EM. Genetic characterization and immunogenicity of coli surface antigen 4 from enterotoxigenic Escherichia coli when it is expressed in a Shigella live-vector strain. Infect Immun 2003; 71:1352-60. [PMID: 12595452 PMCID: PMC148885 DOI: 10.1128/iai.71.3.1352-1360.2003] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The genes that encode the enterotoxigenic Escherichia coli (ETEC) CS4 fimbriae, csaA, -B, -C, -E, and -D', were isolated from strain E11881A. The csa operon encodes a 17-kDa major fimbrial subunit (CsaB), a 40-kDa tip-associated protein (CsaE), a 27-kDa chaperone-like protein (CsaA), a 97-kDa usher-like protein (CsaC), and a deleted regulatory protein (CsaD'). The predicted amino acid sequences of the CS4 proteins are highly homologous to structural and assembly proteins of other ETEC fimbriae, including CS1 and CS2, and to CFA/I in particular. The csaA, -B, -C, -E operon was cloned on a stabilized plasmid downstream from an osomotically regulated ompC promoter. pGA2-CS4 directs production of CS4 fimbriae in both E. coli DH5alpha and Shigella flexneri 2a vaccine strain CVD 1204, as detected by Western blot analysis and bacterial agglutination with anti-CS4 immune sera. Electron-microscopic examination of Shigella expressing CS4 confirmed the presence of fimbriae on the bacterial surface. Guinea pigs immunized with CVD 1204(pGA2-CS4) showed serum and mucosal antibody responses to both the Shigella vector and the ETEC fimbria CS4. Among the seven most prevalent fimbrial antigens of human ETEC, CS4 is the last to be cloned and sequenced. These findings pave the way for CS4 to be included in multivalent ETEC vaccines, including an attenuated Shigella live-vector-based ETEC vaccine.
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Affiliation(s)
- Zeev Altboum
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
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26
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Abstract
The efficiency of any live bacterial vector vaccine hinges on its ability to present sufficient foreign antigen to the human immune system to initiate the desired protective immune response(s). However, synthesis of sufficient levels of heterologous antigen can result in an increase in metabolic burden with an accompanying decrease in the fitness of the live vector, which can ultimately lower desired immune responses to both live vector and heterologous antigen. Here, we explore the underlying mechanisms of metabolic load and propose ways of minimizing such burdens to enhance the fitness and immunogenicity of Salmonella-based live vector vaccines.
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Affiliation(s)
- J E Galen
- Center for Vaccine Development, University of Maryland School of Medicine, 685 W. Baltimore St, Baltimore, MD 21201, USA.
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Wang JY, Pasetti MF, Noriega FR, Anderson RJ, Wasserman SS, Galen JE, Sztein MB, Levine MM. Construction, genotypic and phenotypic characterization, and immunogenicity of attenuated DeltaguaBA Salmonella enterica serovar Typhi strain CVD 915. Infect Immun 2001; 69:4734-41. [PMID: 11447145 PMCID: PMC98559 DOI: 10.1128/iai.69.8.4734-4741.2001] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
A promising live attenuated typhoid vaccine candidate strain for mucosal immunization was developed by introducing a deletion in the guaBA locus of pathogenic Salmonella enterica serovar Typhi strain Ty2. The resultant DeltaguaBA mutant, serovar Typhi CVD 915, has a gene encoding resistance to arsenite replacing the deleted sequence within guaBA, thereby providing a marker to readily identify the vaccine strain. CVD 915 was compared in in vitro and in vivo assays with wild-type strain Ty2, licensed live oral typhoid vaccine strain Ty21a, or attenuated serovar Typhi vaccine strain CVD 908-htrA (harboring mutations in aroC, aroD, and htrA). CVD 915 was less invasive than CVD 908-htrA in tissue culture and was more crippled in its ability to proliferate after invasion. In mice inoculated intraperitoneally with serovar Typhi and hog gastric mucin (to estimate the relative degree of attenuation), the 50% lethal dose of CVD 915 (7.7 x 10(7) CFU) was significantly higher than that of wild-type Ty2 (1.4 x 10(2) CFU) and was only slightly lower than that of Ty21a (1.9 x 10(8) CFU). Strong serum O and H antibody responses were recorded in mice inoculated intranasally with CVD 915, which were higher than those elicited by Ty21a and similar to those stimulated by CVD 908-htrA. CVD 915 also elicited potent proliferative responses in splenocytes from immunized mice stimulated with serovar Typhi antigens. Used as a live vector, CVD 915(pTETlpp) elicited high titers of serum immunoglobulin G anti-fragment C. These encouraging preclinical data pave the way for phase 1 clinical trials with CVD 915.
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Affiliation(s)
- J Y Wang
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
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Altboum Z, Barry EM, Losonsky G, Galen JE, Levine MM. Attenuated Shigella flexneri 2a Delta guaBA strain CVD 1204 expressing enterotoxigenic Escherichia coli (ETEC) CS2 and CS3 fimbriae as a live mucosal vaccine against Shigella and ETEC infection. Infect Immun 2001; 69:3150-8. [PMID: 11292735 PMCID: PMC98271 DOI: 10.1128/iai.69.5.3150-3158.2001] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To construct a prototype hybrid vaccine against Shigella and enterotoxigenic Escherichia coli (ETEC), the genes encoding the production of ETEC CS2 and CS3 fimbriae were isolated and expressed in attenuated Shigella flexneri 2a guaBA strain CVD 1204. The CS2 cotA to -D genes, isolated from ETEC strain C91F, and the CS3 cstA to -H genes, subcloned from plasmid pCS100, were cloned into ~15-copy-number-stabilized pGA1 behind the osmotically regulated ompC promoter, resulting in high expression of both fimbriae. Under nonselective in vitro growth conditions, pGA1-CS2 and pGA1-CS3 were stable in CVD 1204, exhibiting a plasmid loss of only approximately 1% per duplication. Expression of CS2 and CS3 reduced the invasiveness of Shigella for HeLa cells and slowed the intracellular growth rate. Guinea pigs immunized intranasally with CVD 1204(pGA1-CS2) or CVD 1204(pGA1-CS3), or with a mixture of these strains, developed secretory immunoglobulin A (IgA) in tears and serum IgG antibodies against Shigella lipopolysaccharide, CS2, and CS3 antigens. Moreover, the animals were protected against keratoconjunctivitis following conjunctival challenge with virulent S. flexneri 2a strain 2457T. Animals immunized with Shigella expressing CS2 or CS3 developed serum antibodies that agglutinated Shigella as well as an ETEC strain bearing the homologous fimbriae, whereas animals immunized with combined CVD 1204(pGA1-CS2) and CVD 1204(pGA1-CS3) developed antibodies that agglutinated all three test strains. These observations support the feasibility of a multivalent vaccine against shigellosis and ETEC diarrhea consisting of multiple Shigella live vectors expressing relevant ETEC antigens.
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Affiliation(s)
- Z Altboum
- Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
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29
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Orr N, Galen JE, Levine MM. Novel use of anaerobically induced promoter, dmsA, for controlled expression of fragment C of tetanus toxin in live attenuated Salmonella enterica serovar Typhi strain CVD 908-htrA. Vaccine 2001; 19:1694-700. [PMID: 11166893 DOI: 10.1016/s0264-410x(00)00400-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The anaerobically induced promoter dmsA (PdmsA) was adapted to optimize in vivo expression of foreign antigens in attenuated Salmonella enterica serovar Typhi live vector vaccines CVD 908-htrA. PdmsA from Escherichia coli and two derivatives, PdmsA2 and PdmsA3 were cloned into a plasmid driving the expression of a gene encoding tetanus toxin fragment C. Expression of fragment C varied from a low level induced by pTETdmsA, to moderate and high levels induced, respectively, by pTETdmsA2 and pTETdmsA3. Mice were immunized intranasally with CVD 908-htrA harboring pTETdmsA2 or pTETdmsA3, and the serum antitoxin response was compared to that elicited by CVD 908-htrA(pTETnir15) (Pnir15 is a benchmark anaerobically activated promoter). S. Typhi carrying pTETdmsA2 elicited modest tetanus antitoxin titers while S. Typhi harboring pTETdmsA3 generated elevated titers (GMT=55384) that were higher than elicited by pTETnir15 (GMT=4354) (P=0.007). Mice immunized with CVD 908-htrA carrying pTETdmsA3 and pTETnir15 survived tetanus toxin challenge. P(dmsA) derivatives are attractive promoters for in vivo expression of foreign genes in attenuated live vector vaccines.
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MESH Headings
- Anaerobiosis
- Animals
- Antibodies, Bacterial/blood
- Antibodies, Bacterial/immunology
- Antigens, Bacterial/genetics
- Antigens, Bacterial/immunology
- Antigens, Bacterial/toxicity
- Base Sequence
- Blotting, Western
- Cloning, Molecular
- Consensus Sequence/genetics
- Escherichia coli/genetics
- Gene Expression Regulation, Bacterial/drug effects
- Genes, Bacterial/genetics
- Immunoglobulin G/blood
- Immunoglobulin G/immunology
- Mice
- Mice, Inbred BALB C
- Molecular Sequence Data
- Nitrates/pharmacology
- Peptide Fragments/biosynthesis
- Peptide Fragments/genetics
- Peptide Fragments/immunology
- Peptide Fragments/toxicity
- Promoter Regions, Genetic/genetics
- Salmonella Vaccines/genetics
- Salmonella Vaccines/immunology
- Salmonella typhi/genetics
- Salmonella typhi/immunology
- Survival Rate
- Tetanus Toxin/biosynthesis
- Tetanus Toxin/genetics
- Tetanus Toxin/immunology
- Tetanus Toxin/toxicity
- Vaccines, Attenuated/genetics
- Vaccines, Attenuated/immunology
- Vaccines, Synthetic/genetics
- Vaccines, Synthetic/immunology
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Affiliation(s)
- N Orr
- Department of Pediatrics, University of Maryland School of Medicine, Center for Vaccine Development, 685 West Baltimore Street, Baltimore, MD 21201, USA.
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30
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Wang JY, Noriega FR, Galen JE, Barry E, Levine MM. Constitutive expression of the Vi polysaccharide capsular antigen in attenuated Salmonella enterica serovar typhi oral vaccine strain CVD 909. Infect Immun 2000; 68:4647-52. [PMID: 10899868 PMCID: PMC98400 DOI: 10.1128/iai.68.8.4647-4652.2000] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Live oral Ty21a and parenteral Vi polysaccharide vaccines provide significant protection against typhoid fever, albeit by distinct immune mechanisms. Vi stimulates serum immunoglobulin G Vi antibodies, whereas Ty21a, which does not express Vi, elicits humoral and cell-mediated immune responses other than Vi antibodies. Protection may be enhanced if serum Vi antibody as well as cell-mediated and humoral responses can be stimulated. Disappointingly, several new attenuated Salmonella enterica serovar Typhi oral vaccines (e.g., CVD 908-htrA and Ty800) that elicit serum O and H antibody and cell-mediated responses following a single dose do not stimulate serum Vi antibody. Vi expression is regulated in response to environmental signals such as osmolarity by controlling the transcription of tviA in the viaB locus. To investigate if Vi antibodies can be stimulated if Vi expression is rendered constitutive, we replaced P(tviA) in serovar Typhi vaccine CVD 908-htrA with the constitutive promoter P(tac), resulting in CVD 909. CVD 909 expresses Vi even under high-osmolarity conditions and is less invasive for Henle 407 cells. In mice immunized with a single intranasal dose, CVD 909 was more immunogenic than CVD 908-htrA in eliciting serum Vi antibodies (geometric mean titer of 160 versus 49, P = 0.0007), whereas O antibody responses were virtually identical (geometric mean titer of 87 versus 80). In mice challenged intraperitoneally with wild-type serovar Typhi 4 weeks after a single intranasal immunization, the mortality of those immunized with CVD 909 (3 of 8) was significantly lower than that of control mice (10 of 10, P = 0.043) or mice given CVD 908-htrA (9 of 10, P = 0.0065).
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Affiliation(s)
- J Y Wang
- Center for Vaccine Development, Division of Infectious Diseases and Tropical Pediatrics, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
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31
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Pickett TE, Pasetti MF, Galen JE, Sztein MB, Levine MM. In vivo characterization of the murine intranasal model for assessing the immunogenicity of attenuated Salmonella enterica serovar Typhi strains as live mucosal vaccines and as live vectors. Infect Immun 2000; 68:205-13. [PMID: 10603389 PMCID: PMC97122 DOI: 10.1128/iai.68.1.205-213.2000] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Attenuated Salmonella enterica serovar Typhi live vector vaccine strains are highly immunogenic in mice following intranasal but not orogastric inoculation. To elucidate the relationship between organs within which vaccine organisms are found and the induction of specific serum immunoglobulin G (IgG) antibodies, we examined the in vivo distribution of serovar Typhi vaccine strain CVD 908-htrA following intranasal administration. Vaccine organisms were cultured from the nasal lymphoid tissue (NALT), lungs, and Peyer's patches 2 min after intranasal inoculation. Vaccine organisms persisted longer in NALT than in other organs. By decreasing the volume of intranasal inoculum containing 10(9) CFU (from a single 30- or 10-microl dose to four 2.5-microl doses given over the course of 1 h), we were able to significantly reduce the number of vaccine organisms isolated from the lungs (P < 0.05) without reducing the number of vaccine organisms in NALT. Reducing the number of vaccine organisms in the lungs resulted in a significant decrease in the serum tetanus antitoxin response elicited by CVD 908-htrA expressing tetanus toxin fragment C under the control of the redox-responsive nir15 promoter. In contrast, a similar construct expressing tetanus toxin fragment C under control of the constitutive lpp promoter stimulated a strong serum IgG tetanus antitoxin response with both inoculation regimens. The data suggest that following intranasal inoculation, NALT is a sufficient inductive site for elicitation of an immune response against both the live vector and heterologous antigen and, as occurs following oral inoculation of humans, attenuated serovar Typhi vaccine organisms elicit serum IgG responses.
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Affiliation(s)
- T E Pickett
- Center for Vaccine Development, Division of Geographic Medicine, Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
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32
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Galen JE, Nair J, Wang JY, Wasserman SS, Tanner MK, Sztein MB, Levine MM. Optimization of plasmid maintenance in the attenuated live vector vaccine strain Salmonella typhi CVD 908-htrA. Infect Immun 1999; 67:6424-33. [PMID: 10569759 PMCID: PMC97051 DOI: 10.1128/iai.67.12.6424-6433.1999] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The broad objective of the research presented here is to develop a noncatalytic plasmid maintenance system for the stabilization of multicopy expression plasmids encoding foreign antigens in a Salmonella typhi live-vector vaccine strain such as CVD 908-htrA. We have enhanced the maintenance of expression plasmids at two independent levels. First, we removed dependence upon balanced-lethal maintenance systems that involve catalytic enzymes expressed from multicopy plasmids; we accomplished this through incorporation into expression plasmids of a postsegregational killing system based on the noncatalytic hok-sok plasmid addiction system from the antibiotic resistance factor pR1. We also included at least one naturally occurring plasmid partition function in our expression plasmids, which eliminates random segregation of these plasmids, thereby enhancing their inheritance and stability; to accomplish this, we incorporated either the par locus from pSC101, the parA locus from pR1, or both. We monitored the stability of optimized expression plasmids within CVD 908-htrA by quantitating expression of a variant of green fluorescent protein (GFPuv) by using flow cytometry. In this report, we demonstrate the utility of this novel plasmid maintenance system in enhancing the stability of our expression plasmids and go on to show that as the copy number of stabilized plasmids increases, the toxicity of GFPuv synthesis also increases. The implications of these observations for the rational design of immunogenic and protective bacterial live vector vaccines are discussed.
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Affiliation(s)
- J E Galen
- Center for Vaccine Development, Division of Geographic Medicine, Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
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33
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Orr N, Galen JE, Levine MM. Expression and immunogenicity of a mutant diphtheria toxin molecule, CRM(197), and its fragments in Salmonella typhi vaccine strain CVD 908-htrA. Infect Immun 1999; 67:4290-4. [PMID: 10417208 PMCID: PMC96741 DOI: 10.1128/iai.67.8.4290-4294.1999] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mutant diphtheria toxin molecule CRM(197) and fragments thereof were expressed in attenuated Salmonella typhi CVD 908-htrA, and the constructs were tested for their ability to induce serum antitoxin. Initially, expressed proteins were insoluble, and the constructs failed to induce neutralizing antitoxin. Soluble CRM(197) was expressed at low levels by utilizing the hemolysin A secretion system from Escherichia coli.
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Affiliation(s)
- N Orr
- Department of Pediatrics, Division of Infectious Diseases and Tropical Pediatrics, Center for Vaccine Development, Department of Medicine, Division of Geographic Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
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34
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Galen JE, Gomez-Duarte OG, Losonsky GA, Halpern JL, Lauderbaugh CS, Kaintuck S, Reymann MK, Levine MM. A murine model of intranasal immunization to assess the immunogenicity of attenuated Salmonella typhi live vector vaccines in stimulating serum antibody responses to expressed foreign antigens. Vaccine 1997; 15:700-8. [PMID: 9178472 DOI: 10.1016/s0264-410x(96)00227-7] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The lack of a practical small animal model to study the immunogenicity of Salmonella typhi-based live vector vaccines expressing foreign antigens has seriously impeded the vaccine development process. For some foreign antigens, stimulation of serum IgG antibody is the desired, protective immune response. We administered to mice, by orogastric or intranasal (i.n.) routes, attenuated delta aroC delta aroD S. typhi CVD 908 carrying a plasmid encoding fragment C (fragC) of tetanus toxin fused to the eukaryotic cell receptor binding domain of diphtheria toxin (fragC-bDt), and monitored serum antibody. While orogastric inoculation of three doses was not immunogenic, i.n. immunization elicited high titers of serum IgG tetanus antitoxin, generating peak ELISA geometric mean titers (GMT) of 27024 and 35658 with 10(8) and 10(9) c.f.u. dosages, respectively; 10(9) c.f.u. i.n. of an delta aroA S. typhimurium live vector stimulated a peak antitoxin GMT of 376 405. Mice immunized with the S. typhi live vector were 100% protected against challenge with 100 50% lethal doses of tetanus toxin that rapidly killed all control mice. Intranasal immunization with two doses of S. typhi expressing unfused fragment C under control of an anaerobically-activated promoter derived from nirB stimulated significantly higher titers of serum neutralizing antitoxin than fused fragC-bDt controlled by the same promoter (GMT 0.10 AU ml-1 vs 0.01 AU ml-1, P = 0.0095). Two i.n. doses of S typhi encoding fragC under control of powerful constitutive promoter 1pp led to significantly higher peak serum neutralizing antitoxin titers than the otherwise identical construct utilizing the nirB promoter (peak GMT 0.72 AU ml-1 vs 0.10 AU ml-1, P = 0.022). The i.n. route of inoculation of mice may constitute a practical breakthrough that could expedite the development of some S. typhi-based live vector vaccines by allowing, for the first time, quantitative measurement of serum antibody responses to candidate constructs following i.n. mucosal immunization.
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Affiliation(s)
- J E Galen
- Department of Medicine, University of Maryland School of Medicine, Baltimore 21201-1509, USA
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35
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Abstract
The recent expansion of the seventh cholera pandemic into South America emphasizes the need for a safe, long-lasting, protective, and nonreactogenic vaccine for this disease. Since the predominant Vibrio cholerae O1 strains in the world today are of the El Tor biotype, a bivalent vaccine containing both classical and El Tor biotypes may be desirable. We have constructed a new oral vaccine candidate, V. cholerae CVD110 El Tor, Ogawa, from which all toxin genes so far identified in V. cholerae have been deleted. Three of these genes, those encoding cholera toxin (ctx), zonula occludens toxin (zot), and accessory cholera enterotoxin (ace), are located on a 4.5-kb virulence cassette flanked by repetitive sequences (RS1 elements). Homologous recombination between these RS1 elements resulted in the deletion of this virulence cassette to yield V. cholerae CVD109. Insertion of genes encoding mercury resistance (mer) and the cholera toxin B subunit (ctxB) into the hemolysin locus (hlyA) produced CVD110. This insertion serves three purpose. (i) It genetically tags the vaccine strain so as to distinguish it from wild-type V. cholerae O1. (ii) It produces cholera toxin B subunit in order to elicit antitoxic immunity. (iii) It inactivates the hemolysin gene, rendering the strain nonhemolytic on sheep erythrocyte plates. Supernatants from V. cholerae CVD110 cultures are nonreactogenic when assayed in Ussing chambers.
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Affiliation(s)
- J Michalski
- Department of Medicine, University of Maryland School of Medicine, Baltimore 21201
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36
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Trucksis M, Galen JE, Michalski J, Fasano A, Kaper JB. Accessory cholera enterotoxin (Ace), the third toxin of a Vibrio cholerae virulence cassette. Proc Natl Acad Sci U S A 1993; 90:5267-71. [PMID: 8389476 PMCID: PMC46697 DOI: 10.1073/pnas.90.11.5267] [Citation(s) in RCA: 191] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Vibrio cholerae causes the potentially lethal disease cholera through the elaboration of the intestinal secretogen cholera toxin. A second toxin of V. cholerae, Zot, decreases intestinal tissue resistance by modifying intercellular tight junctions. In this report, a third toxin of V. cholerae, Ace (accessory cholera enterotoxin), is described. Ace increases short-circuit current in Ussing chambers and causes fluid secretion in ligated rabbit ileal loops. The predicted protein sequence of Ace shows striking similarity to eukaryotic ion-transporting ATPases, including the product of the cystic fibrosis gene. The gene encoding Ace is located immediately upstream of the genes encoding Zot and cholera toxin. The ctx, zot, and ace genes, which are located on a dynamic sector of the chromosome, comprise a V. cholerae "virulence cassette."
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Affiliation(s)
- M Trucksis
- Department of Medicine, University of Maryland School of Medicine, Baltimore
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37
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Abstract
Vibrio cholerae neuraminidase (NANase) is hypothesized to act synergistically with cholera toxin (CT) and increase the severity of a secretory response by increasing the binding and penetration of CT to enterocytes. To test this hypothesis, the NANase gene (nanH) from V. cholerae Ogawa 395 was first cloned and sequenced. Isogenic wild-type and NANase- V. cholerae 395 strains were then constructed by using suicide vector-mediated mutagenesis. The influence of NANase on CT binding and penetration was examined in vitro by using culture filtrates from these isogenic strains. Fluorescence due to binding of fluorescein-conjugated CT to C57BL/6 and C3H mouse fibroblasts exposed to NANase+ filtrates increased five- and eightfold, respectively, relative to that with NANase- filtrates. In addition, NANase+ filtrates increased the short-circuit current measured in Ussing chambers 65% relative to that with NANase- filtrates, although this difference decreased as production of CT increased. The role of NANase in V. cholerae pathogenesis was examined in vivo by intragastric inoculation of the isogenic strains into CD1 suckling mice. No difference in fluid accumulation ratios was seen at doses of 10(4) to 10(8) CFU, but NANase+ strains produced 18% higher fluid accumulation ratios at 10(9) CFU than NANase- strains when inoculated into nonfasted suckling mice. It is concluded that NANase plays a subtle but significant role in the binding and uptake of CT by susceptible cells under defined conditions.
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Affiliation(s)
- J E Galen
- Department of Medicine, University of Maryland School of Medicine, Baltimore 21201
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Miliotis MD, Galen JE, Kaper JB, Morris JG. Development and testing of a synthetic oligonucleotide probe for the detection of pathogenic Yersinia strains. J Clin Microbiol 1989; 27:1667-70. [PMID: 2768454 PMCID: PMC267638 DOI: 10.1128/jcm.27.7.1667-1670.1989] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
A 24-base oligonucleotide probe specific for a region of the Yersinia enterocolitica virulence plasmid (pYV) associated with HEp-2 cell cytotoxicity and the Sereny reaction was constructed by using sequences flanking critical TnphoA insertions in a subcloned fragment of pYV. This probe, highly specific and sensitive for virulent yersiniae, detected pathogenic Y. enterocolitica isolates in artificially inoculated foods.
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Affiliation(s)
- M D Miliotis
- Department of Medicine, University of Maryland School of Medicine, Baltimore, 21201
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Abstract
The nucleotide sequence of the DNA encoding the ADP-ribosyltransferase (A1) fragment of cholera enterotoxin was determined. A putative precursor of the A1 peptide contains an 18-amino acid leader peptide, and the mature A1 peptide contains 194 amino acids. The primary structure of the A1 fragment from cholera enterotoxin is more related to that from a human enterotoxigenic Escherichia coli than to that from a porcine enterotoxigenic E. coli.
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