RiVax™ Ricin Toxin Vaccine
RiVax™ is Soligenix's proprietary vaccine developed to protect against exposure to ricin toxin and is the most advanced vaccine product in the company's portfolio. With RiVax™, Soligenix is a world leader in ricin toxin vaccine research. The immunogen in RiVax™ induces a protective immune response in animal models of ricin exposure and functionally active antibodies in humans. The immunogen consists of a genetically inactivated subunit ricin A chain that is enzymatically inactive and lacks residual toxicity of the holotoxin.
The development of RiVax™ has been sponsored through a series of overlapping challenge grants (UC1) and cooperative grants (U01) from the NIH, granted to Soligenix and to the University of Texas Southwestern Medical Center (UTSW) where the vaccine originated. One human Phase 1 clinical trial has been completed, and a second trial is currently being conducted. The second clinical trial is being supported by a grant from the Food and Drug Administration (FDA)Orphan Products Division to UTSW. Soligenix and UTSW have collectively received approximately $22 million in grant funding from the NIH for RiVax™. Soligenix has also collaborated with other academic and industrial, and not-for profit institutions for different facets of RiVax™ development. These collaborators and contractors include SRI International, Wadsworth Center of the New York State Department of Health, University of Kansas, Division of Microbiology and Infectious Diseases (DMID) of NIH, Lonza, Inc., and Biocon, Inc.
Results of the first Phase 1 human trial of RiVax™ established that the immunogen was safe and induced antibodies anticipated to protect humans from ricin exposure. The antibodies generated from vaccination, concentrated and purified, were capable of conferring immunity passively to recipient animals, indicating that the vaccine was capable of inducing functionally active antibodies in humans. The outcome of the study was published in the Proceedings of the National Academy of Sciences (Vitetta et al., 2006, PNAS, 105:2268-2273). The second trial, sponsored by UTSW, is currently evaluating a more potent formulation of RiVax™ that contains a conventional adjuvant (salts of aluminum), anticipated to result in higher antibody titers of longer duration in human subjects. Soligenix has adapted the original manufacturing process for the immunogen contained in RiVax™ for large scale manufacturing and is further establishing correlates of the human immune response in non-human primates.
Ricin as a Biological Weapon
Ricin has a long history of use in espionage and warfare. Recent economic surveys have shown that there are over 1 million tons of castor beans produced in the world annually. The global commercial production has the potential to yield approximately 50,000 tons of pure ricin. The fate of much of this ricin in countries outside of the US is unknown. Ricin toxin can constitute up to 5 percent of the total protein of the bean. Ricin is highly stable at room temperature and difficult to inactivate by conventional methods. Because of the high content of ricin in castor beans, ricin toxin can be extracted from the mash produced as a by-product of castor oil production by several simple enrichment steps, and therefore easy to stockpile. While ricin is second in toxicity only to botulinum toxin, it is far easier to obtain, prepare, and use. Before the 1990 war, the Iraqi military had attempted to devise ways to disseminate ricin as an explosive bomb, attempts which were forestalled by the war and ensuing events. Ricin has also been detected in a powder form sent in a letter addressed to Senator Bill Frist in 2004, and several other similar but less publicized incidents. More recently, there have been sporadic reports of ricin stockpiles and attempted use of ricin in the US and Europe.
Once exposed to lethal doses of ricin, the effects are essentially irreversible and symptoms appear more rapidly than symptoms of botulinum intoxication (in a dose-dependent manner). Since its lethality is irreversible after four hours and takes three to five days to kill an individual, immunization after ricin exposure is impractical on a large scale. Since ricin is cleared rapidly from the blood and the symptoms of ricin intoxication mimic the symptoms of other diseases, it is not practical to carry out post-exposure immunization via infusion of neutralizing antibodies in a reliable manner. The current expectation that drives vaccine development is that ricin is most likely to be distributed as an aerosol form, since it is highly lethal by this route.
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