Bacillus anthracis is a Gram-positive, spore-forming, Category A organism that has already been used as aweapon of bioterrorism in the US. Its principal virulence factors are two toxins, Lethal Toxin (LT) and EdemaToxin (ET) and an anti-phagocytic capsule. Although an efficacious vaccine (Biothrax), consisting primarily ofProtective Antigen (PA), is licensed in the US, the need to immunize a large segment of the population on shortnotice in case of attack requires a new vaccine that is less reactogenic and able to elicit a rapid protectiveresponse.The objectives of this project are to identify new antigens from B. anthracis spores (Sub-Project I.1) andvegetative cells (Sub-Project 1.2) that can be included in a new anthrax vaccine. The genes for these antigens willbe cloned, expressed as recombinant proteins and tested for protective activity. To understand better andvisualize the process and location of germination, a new mouse model will be developed, using conditionalexpression of a lux gene in B. anthracis (Sub-Project I. 1). The host immune response to B. anthracis antigens,including the role of T cells and the importance of HLA type, will be characterized using blood/cells from subjectswho have had anthrax or have been immunized with the vaccine (Sub-Project 1.2).Despite availability of new structural information on ET and LT, little is known about their cellular actions orroles in anthrax. These issues will be addressed in Sub-Project 1.3, by exploration of the intracellularconsequences of ET and LT enzymatic activities, alone and together, and evaluation of reagents to block theireffects. Finally, a novel strategy for anthrax immunity, the mucosal-prime/parenteral-boost paradigm using aSalmonella-based live vector vaccine, will be tested (Sub-Project 1.4). With this approach, the host system isprimed with mucosally administered, attenuated S. Typhi expressing PA and/or other antigens from Sub-ProjectsI.1 and 1.2, so that the host response will be more vigorous to subsequent parenteral boosting with PA (Biothrax),recombinant PA, or PA conjugated to the other newly identified antigens from spores or vegetative cells [Sub-Projects 1.1 and 1.2].This research will be carried out by a team of investigators who have extensive experience in microbialpathogenesis, antigen identification, animal models, toxin mechanisms, and vaccine development and testing.The deliverables include new antigens from B. anthracis, tested in murine and NHP systems, compounds withpotential to impede or block the molecular mechanisms by which individuals die of anthrax, and a new mouse model for imaginggermination and bacterial distribution.
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