DESCRIPTION (provided by applicant): Ricin is a highly lethal ribotoxin produced by castor beans. 50,000 tons of ricin are generated each year as a by product of castor oil production. Ricin has a long history of use in espionage and warfare and is classified by the CDC as a Class B biothreat. There is no approved vaccine. Ricin A chain (RTA) has two toxicities in humans: ribosome inactivation and vascular leak syndrome. We previously generated recombinant RTA mutants with single amino acid changes in both sites, and chose the best candidate vaccine based on high yield and stability. This vaccine (RiVax) was developed into a frozen, intramuscular formulation. Rivax is highly effective in protecting mice against ten LD50s of ricin. It was safe and immunogenic in both rabbits and humans. We developed a gavage challenge model for ricin and set up a BSL3 laboratory for aerosol challenges. During the course of our gavage challenge studies, we found that ricin was 1000-10,000 more toxic when delivered by gavage than the older literature had suggested. As a result of this finding, ricin represents a more serious threat to the food and water supply of our civilian population than we had realized previously. Thus there might be a greater need for this vaccine than previously appreciated. Hence, we now propose to develop: 1) a lyophilized formulation of RiVax that is stable at ambient temperatures or 4¿C; 2) an effective intradermal vaccination regimen that does not require needles and should be immunogenic at lower doses; 3) an intranasal formulation that will protect the mucosa against gavaged (and aerosolized) ricin. 4) Normal toxicology studies will be carried out on our best candidate formulations and regimens. Relevance of this research to public health (lav language): It is critical that both our military and civilian populations have access to an approved ricin vaccine that will protect them against both ingested and aerosolized ricin. This proposal represents a critical step in accomplishing this goal.