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Stoll A, Shenton DP, Green AC, Holley JL. Comparative Aspects of Ricin Toxicity by Inhalation. Toxins (Basel) 2023; 15:toxins15040281. [PMID: 37104219 PMCID: PMC10145923 DOI: 10.3390/toxins15040281] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Revised: 03/30/2023] [Accepted: 04/04/2023] [Indexed: 04/28/2023] Open
Abstract
The pathogenesis of ricin toxicity following inhalation has been investigated in many animal models, including the non-human primate (predominantly the rhesus macaque), pig, rabbit and rodent. The toxicity and associated pathology described in animal models are broadly similar, but variation appears to exist. This paper reviews the published literature and some of our own unpublished data and describes some of the possible reasons for this variation. Methodological variation is evident, including method of exposure, breathing parameters during exposure, aerosol characteristics, sampling protocols, ricin cultivar, purity and challenge dose and study duration. The model species and strain used represent other significant sources of variation, including differences in macro- and microscopic anatomy, cell biology and function, and immunology. Chronic pathology of ricin toxicity by inhalation, associated with sublethal challenge or lethal challenge and treatment with medical countermeasures, has received less attention in the literature. Fibrosis may follow acute lung injury in survivors. There are advantages and disadvantages to the different models of pulmonary fibrosis. To understand their potential clinical significance, these factors need to be considered when choosing a model for chronic ricin toxicity by inhalation, including species and strain susceptibility to fibrosis, time it takes for fibrosis to develop, the nature of the fibrosis (e.g., self-limiting, progressive, persistent or resolving) and ensuring that the analysis truly represents fibrosis. Understanding the variables and comparative aspects of acute and chronic ricin toxicity by inhalation is important to enable meaningful comparison of results from different studies, and for the investigation of medical countermeasures.
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Affiliation(s)
- Alexander Stoll
- Defence Science and Technology Laboratory, Salisbury SP4 0JQ, UK
| | - Daniel P Shenton
- Defence Science and Technology Laboratory, Salisbury SP4 0JQ, UK
| | | | - Jane L Holley
- Defence Science and Technology Laboratory, Salisbury SP4 0JQ, UK
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2
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Doering J, Czajka T, Yates JL, Donini O, Mantis NJ. Potency determination of ricin toxin using a monoclonal antibody-based competition assay. J Immunol Methods 2020; 486:112844. [PMID: 32891616 DOI: 10.1016/j.jim.2020.112844] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Revised: 08/04/2020] [Accepted: 08/17/2020] [Indexed: 10/23/2022]
Abstract
Mouse challenge studies with death as an endpoint remain the gold standard in assessing the potency of ricin toxin, a Category B biothreat agent derived from the castor bean (Ricinus communis). However, animal studies are expensive, time consuming and ethically concerning. In an effort to reduce reliance on animals in vaccine development, we developed a monoclonal antibody (MAb)-based ricin competition ELISA (RiCoE) that indicates conformation integrity of ricin toxin. In forced degradation (heat-denaturation) experiments with native ricin holotoxin, we demonstrate a correlation between the decline in MAb reactivity in RiCoE and a corresponding loss of toxin potency in Vero cells (IC50) and mice (LD50). The RiCoE assay was applied to differentially sourced commercial lots of ricin toxin derived from R. communis blends and compared to toxin potency in mice. There was near perfect congruence between RiCoE values with two different MAbs (PB10, SyH7) and ricin potency in the mouse model using morbidity as an endpoint. In conclusion, we propose that RiCoE can serve as a rapid and sensitive substitute to mouse lethal dose challenge studies as a means to determine ricin toxin potency and will be valuable at various stages of vaccine development.
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Affiliation(s)
- Jennifer Doering
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States of America
| | - Timothy Czajka
- Department of Biomedical Sciences, University at Albany, Albany, NY 12201, United States of America
| | - Jennifer L Yates
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States of America
| | - Oreola Donini
- Soligenix, Inc., Princeton, NJ 08540, United States of America
| | - Nicholas J Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States of America; Department of Biomedical Sciences, University at Albany, Albany, NY 12201, United States of America.
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3
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Slyke GV, Ehrbar DJ, Doering J, Yates JL, Vitetta ES, Donini O, Mantis NJ. Endpoint and epitope-specific antibody responses as correlates of vaccine-mediated protection of mice against ricin toxin. Vaccine 2020; 38:6721-6729. [PMID: 32891474 DOI: 10.1016/j.vaccine.2020.08.047] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Revised: 08/11/2020] [Accepted: 08/18/2020] [Indexed: 12/17/2022]
Abstract
The successful licensure of vaccines for biodefense is contingent upon the availability of well-established correlates of protection (CoP) in at least two animal species that can be applied to humans, without the need to assess efficacy in the clinic. In this report we describe a multivariate model that combines pre-challenge serum antibody endpoint titers (EPT) and values derived from an epitope profiling immune-competition capture (EPICC) assay as a predictor in mice of vaccine-mediated immunity against ricin toxin (RT), a Category B biothreat. EPICC is a modified competition ELISA in which serum samples from vaccinated mice were assessed for their ability to inhibit the capture of soluble, biotinylated (b)-RT by a panel of immobilized monoclonal antibodies (mAbs) directed against four immunodominant toxin-neutralizing regions on the enzymatic A chain (RTA) of RT. In a test cohort of mice (n = 40) vaccinated with suboptimal doses of the RTA subunit vaccine, RiVax®, we identified two mAbs, PB10 and SyH7, which had EPICC inhibition values in pre-challenge serum samples that correlated with survival following a challenge with 5 × LD50 of RT administered by intraperitoneal (IP) injection. Analysis of a larger cohort of mice (n = 645) revealed that a multivariate model combining endpoint titers and EPICC values for PB10 and SyH7 as predictive variables had significantly higher statistical power than any one of the independent variables alone. Establishing the correlates of vaccine-mediated protection in mice represents an important steppingstone in the development of RiVax® as a medical countermeasure under the United States Food and Drug Administration's "Animal Rule."
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Affiliation(s)
- Greta Van Slyke
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Dylan J Ehrbar
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Jennifer Doering
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Jennifer L Yates
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Ellen S Vitetta
- Department of Immunology and Microbiology, University of Texas Southwestern Medical School, Dallas, TX, United States
| | | | - Nicholas J Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States.
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4
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Plant Ribosome-Inactivating Proteins: Progesses, Challenges and Biotechnological Applications (and a Few Digressions). Toxins (Basel) 2017; 9:toxins9100314. [PMID: 29023422 PMCID: PMC5666361 DOI: 10.3390/toxins9100314] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Revised: 09/29/2017] [Accepted: 10/03/2017] [Indexed: 12/11/2022] Open
Abstract
Plant ribosome-inactivating protein (RIP) toxins are EC3.2.2.22 N-glycosidases, found among most plant species encoded as small gene families, distributed in several tissues being endowed with defensive functions against fungal or viral infections. The two main plant RIP classes include type I (monomeric) and type II (dimeric) as the prototype ricin holotoxin from Ricinus communis that is composed of a catalytic active A chain linked via a disulphide bridge to a B-lectin domain that mediates efficient endocytosis in eukaryotic cells. Plant RIPs can recognize a universally conserved stem-loop, known as the α-sarcin/ ricin loop or SRL structure in 23S/25S/28S rRNA. By depurinating a single adenine (A4324 in 28S rat rRNA), they can irreversibly arrest protein translation and trigger cell death in the intoxicated mammalian cell. Besides their useful application as potential weapons against infected/tumor cells, ricin was also used in bio-terroristic attacks and, as such, constitutes a major concern. In this review, we aim to summarize past studies and more recent progresses made studying plant RIPs and discuss successful approaches that might help overcoming some of the bottlenecks encountered during the development of their biomedical applications.
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Jetzt AE, Li XP, Tumer NE, Cohick WS. Toxicity of ricin A chain is reduced in mammalian cells by inhibiting its interaction with the ribosome. Toxicol Appl Pharmacol 2016; 310:120-128. [PMID: 27639428 DOI: 10.1016/j.taap.2016.09.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Revised: 09/08/2016] [Accepted: 09/10/2016] [Indexed: 01/11/2023]
Abstract
Ricin is a potent ribotoxin that is considered a bioterror threat due to its ease of isolation and possibility of aerosolization. In yeast, mutation of arginine residues away from the active site results in a ricin toxin A chain (RTA) variant that is unable to bind the ribosome and exhibits reduced cytotoxicity. The goal of the present work was to determine if these residues contribute to ribosome binding and cytotoxicity of RTA in mammalian cells. The RTA mutant R193A/R235A did not interact with mammalian ribosomes, while a G212E variant with a point mutation near its active site bound ribosomes similarly to wild-type (WT) RTA. R193A/R235A retained full catalytic activity on naked RNA but had reduced activity on mammalian ribosomes. To determine the effect of this mutant in intact cells, pre R193A/R235A containing a signal sequence directing it to the endoplasmic reticulum and mature R193A/R235A that directly targeted cytosolic ribosomes were each expressed. Depurination and protein synthesis inhibition were reduced by both pre- and mature R193A/R235A relative to WT. Protein synthesis inhibition was reduced to a greater extent by R193A/R235A than by G212E. Pre R193A/R235A caused a greater reduction in caspase activation and loss of mitochondrial membrane potential than G212E relative to WT RTA. These findings indicate that an RTA variant with reduced ribosome binding is less toxic than a variant with less catalytic activity but normal ribosome binding activity. The toxin-ribosome interaction represents a novel target for the development of therapeutics to prevent or treat ricin intoxication.
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Affiliation(s)
- Amanda E Jetzt
- Department of Animal Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901-8520, United States
| | - Xiao-Ping Li
- Department of Plant Biology and Pathology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901-8520, United States
| | - Nilgun E Tumer
- Department of Plant Biology and Pathology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901-8520, United States
| | - Wendie S Cohick
- Department of Animal Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901-8520, United States.
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6
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Vance DJ, Mantis NJ. Progress and challenges associated with the development of ricin toxin subunit vaccines. Expert Rev Vaccines 2016; 15:1213-22. [PMID: 26998662 PMCID: PMC5193006 DOI: 10.1586/14760584.2016.1168701] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The past several years have seen major advances in the development of a safe and efficacious ricin toxin vaccine, including the completion of two Phase I clinical trials with two different recombinant A subunit (RTA)-based vaccines: RiVax™ and RVEc™ adsorbed to aluminum salt adjuvant, as well as a non-human primate study demonstrating that parenteral immunization with RiVax elicits a serum antibody response that was sufficient to protect against a lethal dose aerosolized ricin exposure. One of the major obstacles moving forward is assessing vaccine efficacy in humans, when neither ricin-specific serum IgG endpoint titers nor toxin-neutralizing antibody levels are accepted as definitive predictors of protective immunity. In this review we summarize ongoing efforts to leverage recent advances in our understanding of RTA-antibody interactions at the structural level to develop novel assays to predict vaccine efficacy in humans.
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Affiliation(s)
- David J. Vance
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
| | - Nicholas J. Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
- Department of Biomedical Sciences, University at Albany, Albany, New York, USA
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7
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Zhang T, Yang H, Kang L, Gao S, Xin W, Yao W, Zhuang X, Ji B, Wang J. Strong protection against ricin challenge induced by a novel modified ricin A-chain protein in mouse model. Hum Vaccin Immunother 2016; 11:1779-87. [PMID: 26038805 PMCID: PMC4514271 DOI: 10.1080/21645515.2015.1038446] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Ricin toxin (RT) is an extremely potent toxin derived from the castor bean plant. As a possible bioterrorist weapon, it was categorized as a level B agent in international society. With the growing awareness and concerns of the “white powder incident” in recent years, it is indispensable to develop an effective countermeasure against RT intoxication. In this study we used site-directed mutagenesis and polymerase chain reaction (PCR) techniques to modify the gene of ricin A-chain (RTA). As a result, we have generated a mutated and truncated ricin A-chain (mtRTA) vaccine antigen by E.coli strain. The cytotoxicity assay was used to evaluate the safety of the as-prepared mtRTA antigen, and the results showed that there was no residual toxicity observed when compared to the recombinant RTA (rRTA) or native RT. Furthermore, BALB/c mice were subcutaneously (s.c.) vaccinated with mtRTA 3 times at an interval of 2 weeks, and then the survivals were evaluated after intraperitoneal (i.p.) or intratracheal challenge of RT. The vaccinated mice developed a strong protective immune response that was wholly protective against 40 × LD50 of RT i.p. injection or 20 × LD50 of RT intratracheal spraying. The mtRTA antigen has great potential to be a vaccine candidate for future application in humans.
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Key Words
- ELISA, enzyme-linked immunosorbent assay
- FBS, fetal bovine serum
- HRP, horseradish peroxidase
- IPTG, isopropyl-1-thio-β-galactopyranoside
- LD50, median lethal dose
- RT, ricin toxin
- RTA, ricin toxin A chain
- RTB, ricin toxin B chain
- SD, standard deviation
- i.p, intraperitoneally
- i.p., intraperitoneal
- immunity
- intratracheal
- mRTA, mutated RTA
- mtRTA, mutated and truncated RTA
- mutant
- rRTA, recombinant RTA
- ricin
- s.c., subcutaneously subcutaneous
- toxicity
- toxin
- truncation
- vaccine
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Affiliation(s)
- Tao Zhang
- a State Key Laboratory of Pathogen and Biosecurity; Beijing Institute of Microbiology and Epidemiology ; Beijing , China
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8
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Wang J, Gao S, Xin W, Kang L, Xu N, Zhang T, Liu W, Wang J. A novel recombinant vaccine protecting mice against abrin intoxication. Hum Vaccin Immunother 2016; 11:1361-7. [PMID: 26086588 PMCID: PMC4514378 DOI: 10.1080/21645515.2015.1008879] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Abrin toxin (AT) consisting of an A chain and a B chain is a potential agent for bioterrorism and an effective vaccine against AT poisoning is urgently required. In this study, AT B chain (ATB) was successfully expressed in the Escherichia coli (E. coli) and assessed the protection capacity against AT intoxication. The recombinant ATB (rATB) subunit induces a good immune response after 4 immunizations. All BALB/c mice immunized intraperitoneally (i.p.) with the purified rATB protein survived after challenged with 5 × LD50 of AT. Transfusion of sera from immunized mice provided passive protection in naive mice. Furthermore, histological findings showed that immunization with rATB decreased the severity of toxin-related tissue damage. This work indicates that the rATB protein may be a promising vaccine candidate against human exposure to AT.
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Key Words
- AT, abrin toxin
- ATB, abrin toxin B chain
- B chain
- E. coli, Escherichia coli
- ELISA, enzyme-linked immunosorbent assay
- LD50, 50% lethal dose
- PBS, phosphate-buffered saline solution
- RT, ricin toxin
- RTB, ricin toxin B chain
- SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis
- abrin toxin
- bioterrorism
- i.p, intraperitoneal or intraperitoneally
- immunogen
- pAb, polyclonal antibody
- vaccine candidate
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Affiliation(s)
- Junhong Wang
- a State Key Laboratory of Pathogen and Biosecurity; Beijing Institute of Microbiology and Epidemiology ; Beijing , PR China
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Brey RN, Mantis NJ, Pincus SH, Vitetta ES, Smith LA, Roy CJ. Recent advances in the development of vaccines against ricin. Hum Vaccin Immunother 2016; 12:1196-201. [PMID: 26810367 DOI: 10.1080/21645515.2015.1124202] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
Several promising subunit vaccines against ricin toxin (RT) have been developed during the last decade and are now being tested for safety and immunogenicity in humans and for efficacy in nonhuman primates. The incentive to develop a preventive vaccine as a countermeasure against RT use as a bioweapon is based on the high toxicity of RT after aerosol exposure, its environmental stability, abundance, and ease of purification. RT is the second most lethal biological toxin and is considered a "universal toxin" because it can kill all eukaryotic cells through binding to ubiquitous cell surface galactosyl residues. RT has two subunits conjoined by a single disulfide linkage: RTB, which binds galactosyl residues and RTA which enzymatically inactivates ribosomes intracellularly by cleavage ribosomal RNA. Attenuation of toxicity by elimination of the active site or introduction of other structural mutations of RTA has generated two similar clinical subunit vaccine candidates which induce antibodies in both humans and nonhuman primates. In rhesus macaques, inhaled RT causes rapid lung necrosis and fibrosis followed by death. After parenteral vaccination with RTA vaccine, macaques can be protected against aerosol RT exposure, suggesting that circulating antibodies can protect lung mucosa. Vaccination induces RT-neutralizing antibodies, the most likely correlate of protection. Macaques responded to conformational determinants in an RTA vaccine formulation, indicating preservation of RTA structure during initial manufacture. Comparative mapping studies have also demonstrated that macaques and humans recognize the same epitopes, significant in the study of macaques as a model during development of vaccines which cannot be tested for efficacy in humans.
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Affiliation(s)
| | - Nicholas J Mantis
- b Division of Infectious Disease , Wadsworth Center, New York State Department of Health, Albany, NY, USA Department of Biomedical Sciences, University of Albany School of Public Health , Albany , NY , USA
| | - Seth H Pincus
- c Departments of Pediatrics and Microbiology , Louisiana State University School of Medicine, Children's Hospital , New Orleans , LA , USA
| | - Ellen S Vitetta
- d Departments of Immunology and Microbiology , The University of Texas Southwestern Medical Center , Dallas , TX , USA
| | - Leonard A Smith
- e Medical Countermeasures Technology, US Army Medical Research Institute of Infectious Diseases , Fort Detrick , MD , USA
| | - Chad J Roy
- f Division of Microbiology, Tulane National Primate Research Center , Covington , LA , USA.,g Department of Microbiology and Immunology , Tulane School of Medicine , New Orleans , LA , USA
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Pittman PR, Reisler RB, Lindsey CY, Güereña F, Rivard R, Clizbe DP, Chambers M, Norris S, Smith LA. Safety and immunogenicity of ricin vaccine, RVEc™, in a Phase 1 clinical trial. Vaccine 2015; 33:7299-7306. [PMID: 26546259 DOI: 10.1016/j.vaccine.2015.10.094] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Revised: 07/24/2015] [Accepted: 10/24/2015] [Indexed: 12/23/2022]
Abstract
Ricin is a potent toxin and potential bioterrorism weapon for which no specific licensed countermeasures are available. We report the safety and immunogenicity of the ricin vaccine RVEc™ in a Phase 1 (N=30) multiple-dose, open-label, non-placebo-controlled, dose-escalating (20, 50, and 100μg), single-center study. Each subject in the 20- and 50-μg dose groups (n=10 for each group) received three injections at 4-week intervals and was observed carefully for untoward effects of the vaccine; blood was drawn at predetermined intervals after each dose for up to 1 year. RVEc™ was safe and well tolerated at the 20- and 50-μg doses. The most common adverse events were pain at the injection site and headache. Of the 10 subjects who received a single 100-μg dose, two developed elevated creatine phosphokinase levels, which resolved without sequelae. No additional doses were administered to subjects in the 100-μg group. Immunogenicity of the vaccine was evaluated by measuring antibody response using the well standardized enzyme-linked immunosorbent assay (ELISA) and toxin neutralization assay (TNA). Of the subjects in the 20- and 50-μg dose groups, 100% achieved ELISA anti-ricin IgG titers of 1:500 to 1:121,500 and 50% produced neutralizing anti-ricin antibodies measurable by TNA. Four subjects in the 50-μg group received a single booster dose of RVEc™ 20-21 months after the initial dose. The single booster was safe and well tolerated, resulting in no serious adverse events, and significantly enhanced immunogenicity of the vaccine in human subjects. Each booster recipient developed a robust anamnestic response with ELISA anti-ricin IgG titers of 1:13,500 to 1:121,500 and neutralizing antibody titers of 1:400 to 1:3200. Future studies will attempt to optimize dose, scheduling, and route of administration. This study is registered at clinicaltrials.gov (NCT01317667 and NCT01846104).
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Affiliation(s)
- Phillip R Pittman
- US Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Fort Detrick, MD 21702-5011, USA.
| | - Ronald B Reisler
- MedStar Georgetown University Hospital, 7503 Surratts Road, Clinton, MD 20735, USA
| | - Changhong Y Lindsey
- US Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Fort Detrick, MD 21702-5011, USA
| | | | - Robert Rivard
- US Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Fort Detrick, MD 21702-5011, USA
| | - Denise P Clizbe
- US Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Fort Detrick, MD 21702-5011, USA
| | - Matthew Chambers
- US Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Fort Detrick, MD 21702-5011, USA
| | - Sarah Norris
- US Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Fort Detrick, MD 21702-5011, USA
| | - Leonard A Smith
- US Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Fort Detrick, MD 21702-5011, USA
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11
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Thermostable ricin vaccine protects rhesus macaques against aerosolized ricin: Epitope-specific neutralizing antibodies correlate with protection. Proc Natl Acad Sci U S A 2015; 112:3782-7. [PMID: 25775591 DOI: 10.1073/pnas.1502585112] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Ricin toxin (RT) is the second most lethal toxin known; it has been designated by the CDC as a select agent. RT is made by the castor bean plant; an estimated 50,000 tons of RT are produced annually as a by-product of castor oil. RT has two subunits, a ribotoxic A chain (RTA) and galactose-binding B chain (RTB). RT binds to all mammalian cells and once internalized, a single RTA catalytically inactivates all of the ribosomes in a cell. Administered as an aerosol, RT causes rapid lung damage and fibrosis followed by death. There are no Food and Drug Administration-approved vaccines and treatments are only effective in the first few hours after exposure. We have developed a recombinant RTA vaccine that has two mutations V76M/Y80A (RiVax). The protein is expressed in Escherichia coli and is nontoxic and immunogenic in mice, rabbits, and humans. When vaccinated mice are challenged with injected, aerosolized, or orally administered (gavaged) RT, they are completely protected. We have now developed a thermostable, aluminum-adjuvant-containing formulation of RiVax and tested it in rhesus macaques. After three injections, the animals developed antibodies that completely protected them from a lethal dose of aerosolized RT. These antibodies neutralized RT and competed to varying degrees with a panel of neutralizing and nonneutralizing mouse monoclonal antibodies known to recognize specific epitopes on native RTA. The resulting antibody competition profile could represent an immunologic signature of protection. Importantly, the same signature was observed using sera from RiVax-immunized humans.
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12
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Rudolph MJ, Vance DJ, Cheung J, Franklin MC, Burshteyn F, Cassidy MS, Gary EN, Herrera C, Shoemaker CB, Mantis NJ. Crystal structures of ricin toxin's enzymatic subunit (RTA) in complex with neutralizing and non-neutralizing single-chain antibodies. J Mol Biol 2014; 426:3057-68. [PMID: 24907552 PMCID: PMC4128236 DOI: 10.1016/j.jmb.2014.05.026] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2014] [Revised: 05/17/2014] [Accepted: 05/25/2014] [Indexed: 10/25/2022]
Abstract
Ricin is a select agent toxin and a member of the RNA N-glycosidase family of medically important plant and bacterial ribosome-inactivating proteins. In this study, we determined X-ray crystal structures of the enzymatic subunit of ricin (RTA) in complex with the antigen binding domains (VHH) of five unique single-chain monoclonal antibodies that differ in their respective toxin-neutralizing activities. None of the VHHs made direct contact with residues involved in RTA's RNA N-glycosidase activity or induced notable allosteric changes in the toxin's subunit. Rather, the five VHHs had overlapping structural epitopes on the surface of the toxin and differed in the degree to which they made contact with prominent structural elements in two folding domains of the RTA. In general, RTA interactions were influenced most by the VHH CDR3 (CDR, complementarity-determining region) elements, with the most potent neutralizing antibody having the shortest and most conformationally constrained CDR3. These structures provide unique insights into the mechanisms underlying toxin neutralization and provide critically important information required for the rational design of ricin toxin subunit vaccines.
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Affiliation(s)
| | - David J Vance
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA
| | - Jonah Cheung
- New York Structural Biology Center, New York, NY 10027, USA
| | | | | | | | - Ebony N Gary
- New York Structural Biology Center, New York, NY 10027, USA
| | - Cristina Herrera
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA; Department of Biomedical Sciences, University at Albany, Albany, NY 12201, USA
| | | | - Nicholas J Mantis
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA; Department of Biomedical Sciences, University at Albany, Albany, NY 12201, USA.
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13
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O'Hara JM, Kasten-Jolly JC, Reynolds CE, Mantis NJ. Localization of non-linear neutralizing B cell epitopes on ricin toxin's enzymatic subunit (RTA). Immunol Lett 2014; 158:7-13. [PMID: 24269767 PMCID: PMC4070743 DOI: 10.1016/j.imlet.2013.11.009] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2013] [Accepted: 11/07/2013] [Indexed: 12/16/2022]
Abstract
Efforts to develop a vaccine for ricin toxin are focused on identifying highly immunogenic, safe, and thermostable recombinant derivatives of ricin's enzymatic A subunit (RTA). As a means to guide vaccine design, we have embarked on an effort to generate a comprehensive neutralizing and non-neutralizing B cell epitope map of RTA. In a series of previous studies, we identified three spatially distinct linear (continuous), neutralizing epitopes on RTA, as defined by monoclonal antibodies (mAbs) PB10 (and R70), SyH7, and GD12. In this report we now describe a new collection of 19 toxin-neutralizing mAbs that bind non-linear epitopes on RTA. The most potent toxin-neutralizing mAbs in this new collection, namely WECB2, TB12, PA1, PH12 and IB2 each had nanamolar (or sub-nanomolar) affinities for ricin and were each capable of passively protecting mice against a 5-10xLD50 toxin challenge. Competitive binding assays by surface plasmon resonance revealed that WECB2 binds an epitope that overlaps with PB10 and R70; TB12, PA1, PH12 recognize epitope(s) close to or overlapping with SyH7's epitope; and GD12 and IB2 recognize epitopes that are spatially distinct from all other toxin-neutralizing mAbs. We estimate that we have now accounted for ∼75% of the predicted epitopes on the surface of RTA and that toxin-neutralizing mAbs are directed against a very limited number of these epitopes. Having this information provides a framework for further refinement of RTA mutagenesis and vaccine design.
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Affiliation(s)
- Joanne M O'Hara
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States; Department of Biomedical Sciences, University at Albany School of Public Health, Albany, NY 12201, United States
| | - Jane C Kasten-Jolly
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Claire E Reynolds
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Nicholas J Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States; Department of Biomedical Sciences, University at Albany School of Public Health, Albany, NY 12201, United States.
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Chimeric plantibody passively protects mice against aerosolized ricin challenge. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2014; 21:777-82. [PMID: 24574537 DOI: 10.1128/cvi.00003-14] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Recent incidents in the United States and abroad have heightened concerns about the use of ricin toxin as a bioterrorism agent. In this study, we produced, using a robust plant-based platform, four chimeric toxin-neutralizing monoclonal antibodies that were then evaluated for the ability to passively protect mice from a lethal-dose ricin challenge. The most effective antibody, c-PB10, was further evaluated in mice as a therapeutic following ricin exposure by injection and inhalation.
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15
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Wang J, Gao S, Zhang T, Kang L, Cao W, Xu N, Liu W, Wang J. A recombinant chimeric protein containing B chains of ricin and abrin is an effective vaccine candidate. Hum Vaccin Immunother 2014; 10:938-44. [PMID: 24509607 DOI: 10.4161/hv.27870] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Both ricin toxin (RT) and abrin toxin (AT) are 2 important toxin agents as potantial bioweapons. A dual subunit vaccine against RT and AT exposure is a promising option for developing prophylactic vaccination. In this study, we constructed a dual vaccine with RT B chain and AT B chain named RTB-ATB. The RTB-ATB chimeric protein was expressed in Escherichia coli (E. coli), and the purified protein was used to evaluate the immune response by a 2 × 2 × 2 × 2 factorial design. The main effects included dose of RTB-ATB, route of immunization injection, immunization time interval, and dose of native toxins challenge. For 2 × LD(50) challenge of RT or AT, 100% of the RTB-ATB immunized mice survived and regained or exceeded their initial weights within 10 days. For 4 × LD(50) challenge, different routes of immunization injection caused significant difference (P < 0.05), intraperitoneal (i.p.) administration of immunogen protected mice better than the subcutaneous (s.c.) administration. In conclusion, when administered i.p. to mice with 25 μg per mouse and immunization time interval Π in the absence of adjuvant, the chimeric protein elicited a stronger immune response and protected the animals from a dose of native toxins which was 4 times higher than their LD(50) in unvaccinated mice. Besides, the RTB-ATB chimeric protein could induce specific neutralizing antibodies against these 2 toxins. We anticipate that this study will open new possibilities in the preparation of RTB-ATB dual subunit vaccine against the exposure to deadly RT and AT.
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Affiliation(s)
- Junhong Wang
- State Key Laboratory of Pathogen and Biosecurity; Institute of Microbiology and Epidemiology; Academy of Military Medical Sciences; Fengtai District, Beijing, PR China; Tianjin Key Lab for Biomarkers Occupational and Environmental Hazard; Medical College of Chinese People's Armed Police Force; Tianjin, PR China
| | - Shan Gao
- State Key Laboratory of Pathogen and Biosecurity; Institute of Microbiology and Epidemiology; Academy of Military Medical Sciences; Fengtai District, Beijing, PR China
| | - Tao Zhang
- State Key Laboratory of Pathogen and Biosecurity; Institute of Microbiology and Epidemiology; Academy of Military Medical Sciences; Fengtai District, Beijing, PR China
| | - Lin Kang
- State Key Laboratory of Pathogen and Biosecurity; Institute of Microbiology and Epidemiology; Academy of Military Medical Sciences; Fengtai District, Beijing, PR China
| | - Wuchun Cao
- State Key Laboratory of Pathogen and Biosecurity; Institute of Microbiology and Epidemiology; Academy of Military Medical Sciences; Fengtai District, Beijing, PR China
| | - Na Xu
- Institute of Military Veterinary; Academy of Military Medical Sciences; Changchun, PR China
| | - Wensen Liu
- Institute of Military Veterinary; Academy of Military Medical Sciences; Changchun, PR China
| | - Jinglin Wang
- State Key Laboratory of Pathogen and Biosecurity; Institute of Microbiology and Epidemiology; Academy of Military Medical Sciences; Fengtai District, Beijing, PR China
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16
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Bhaskaran M, Didier PJ, Sivasubramani SK, Doyle LA, Holley J, Roy CJ. Pathology of lethal and sublethal doses of aerosolized ricin in rhesus macaques. Toxicol Pathol 2013; 42:573-81. [PMID: 23761937 DOI: 10.1177/0192623313492248] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Ricin toxin, a type 2 ribosome-inactivating protein and a category B bioterrorism agent, is produced from the seeds of castor oil plant (Ricinus communis). Chronic pathological changes in survivors of aerosolized ricin exposure have not been reported in primates. Here we compare and contrast the pathological changes manifested between rhesus macaques (RM) that succumbed to lethal dose of ricin (group I) and survivor RM exposed to low dose of ricin (group II). All animals in group I exhibited severe diffuse, necrotizing bronchiolitis and alveolitis with fibrinopurulent bronchointerstitial pneumonia, massive alveolar, perivascular and peribronchial/bronchiolar edema with hemorrhage, and necropurulent and hemorrhagic tracheobronchial lymphadenitis. All animals from group II had multifocal, fibrosing interstitial pneumonia with prominent alveolar histiocytosis and type II pneumocyte hyperplasia. Subacute changes like infiltration by lymphocytes and plasma cells and persistence of edematous fluid were occasionally present in lung and tracheobronchial lymph nodes. The changes appear to be a continuum wherein the inflammatory response shifts from an acute to subacute/chronic reparative process if the animals can survive the initial insult.
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Affiliation(s)
- Manoj Bhaskaran
- 1Infectious Disease Aerobiology, Division of Microbiology, Tulane National Primate Research Center, Covington, Louisiana, USA
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17
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Comparative efficacy of two leading candidate ricin toxin a subunit vaccines in mice. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2013; 20:789-94. [PMID: 23515013 DOI: 10.1128/cvi.00098-13] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The two leading ricin toxin vaccine candidates, RVEc and RiVax, are recombinant derivatives of the toxin's 267-amino-acid enzymatic A chain (RTA). RVEc is truncated at the C terminus (residues 199 to 267) to improve protein thermostability, while RiVax has two point mutations (V76M and Y80A) that eliminate the RNA N-glycosidase activity of RTA, as well as its ability to induce vascular leak syndrome. The two vaccines have never been directly compared in terms of their ability to stimulate RTA-specific antibodies (Abs), toxin-neutralizing activity (TNA), or protective immunity. To address this issue, groups of female BALB/c mice were immunized two or three times with Alhydrogel-adsorbed RiVax or RVEc at a range of doses (0.3 to 20 μg) and then challenged with 10 50% lethal doses (LD(50)s) of ricin. We found that the vaccines were equally effective at eliciting protective immunity at the doses tested. There were, however, quantitative differences in the antibody responses. RVEc tended to elicit higher levels of ricin-specific RTA IgG and TNA than did RiVax. Pepscan analysis revealed that serum Abs elicited by RVEc were skewed toward a solvent-exposed immunodominant α-helix known to be the target of potent toxin-neutralizing Abs. Finally, immunodepletion experiments suggest that the majority of toxin-neutralizing Abs elicited by RiVax were confined to residues 1 to 198, possibly explaining the equal effectiveness of RVEc as a vaccine.
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O'Hara JM, Yermakova A, Mantis NJ. Immunity to ricin: fundamental insights into toxin-antibody interactions. Curr Top Microbiol Immunol 2012; 357:209-41. [PMID: 22113742 PMCID: PMC4433546 DOI: 10.1007/82_2011_193] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Ricin toxin is an extraordinarily potent inducer of cell death and inflammation. Ricin is also a potent provocateur of the humoral immune system, eliciting a mixture of neutralizing, non-neutralizing and even toxin-enhancing antibodies. The characterization of dozens of monoclonal antibodies (mAbs) against the toxin's enzymatic (RTA) and binding (RTB) subunits has begun to reveal fundamental insights into the underlying mechanisms by which antibodies neutralize (or fail to neutralize) ricin in systemic and mucosal compartments. This information has had immediate applications in the design, development and evaluation of ricin subunit vaccines and immunotherapeutics.
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Affiliation(s)
- Joanne M. O'Hara
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, 120 New Scotland Avenue, Albany, NY 12208, USA; Department of Biomedical Sciences, University at Albany School of Public Health, Albany, NY 12201, USA
| | - Anastasiya Yermakova
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, 120 New Scotland Avenue, Albany, NY 12208, USA; Department of Biomedical Sciences, University at Albany School of Public Health, Albany, NY 12201, USA
| | - Nicholas J. Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, 120 New Scotland Avenue, Albany, NY 12208, USA; Department of Biomedical Sciences, University at Albany School of Public Health, Albany, NY 12201, USA
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