A Novel Recombinant Protein Vaccine Against Ricin Toxin

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DESCRIPTION (provided by applicant): Ricin is a highly lethal toxin produced by castor beans. It is readily available, easy to make, and stockpile. Ricin has a long history of use in espionage and warfare with a documented 750 cases of intoxication. Ricin is classified by the CDC as a Class B biothreat. In the 1990s, the U.S. Military became interested in developing a vaccine against ricin after obtaining information that this toxin was being stockpiled by terrorist organizations. A ricin toxoid is protective in primates, but it is quite toxic and did not receive FDA approval. We have generated three recombinant mutants of ricin's A chain which are devoid of both vascular leak activity and enzymatic activity in mice. When injected i.m., these mutants protect mice against very large doses of injected ricin. Our goal is to develop one of these mutants into an inexpensive, safe, effective, stable, and "user-friendly" vaccine which can be administered to large groups of people. The specific Aims of this proposal are: 1) to optimize production, purification, formulation and stability of the vaccine. 2) to determine whether the vaccine will protect mice against aerosolized as well as intraperitoneal (i.p.) ricin challenge and if so, the best method of immunization (i.m., oral, or intranasal) to protect animals for the longest period of time and 3) to produce a small good laboratory practice (GLP) batch of the best candidate vaccine and use the best route of administration to immunize six adult baboons (three males and three females). When these three aims are completed, the vaccine should be ready for acute toxicology studies in two species and scale-up for Phase 1 clinical trials in humans.