Francisella tularensis is a Gram-negative facultative intracellular bacterial pathogen that causes tularemia, a serious and potentially fatal disease. Because F. tularensis has an extraordinarily high infectivity, causes serious morbidity and mortality, is relatively easily dispersed, and is readily cultured on a large scale, it is also considered a potential agent of biological warfare and bioterrorism. At present, there is no approved vaccine for the prevention of tularemia. Although a live attenuated vaccine (LVS) for tularemia has been developed, the vaccine has two major deficiencies. First, in human challenge studies, the vaccine is not fully protective against exposure to relatively low numbers of organisms (10¿50) compared with substantially higher exposures that could potentially result from a bioterrorist attack. Second, the vaccine retains significant virulence, and its safety in children is uncertain and in immunocompromised individuals highly doubtful.

In prior vaccine work with Legionella pneumophila and Mycobacterium tuberculosis, we have demonstrated that the major secreted proteins of these intracellular pathogens are immunodominant molecules that can be formulated into highly potent vaccines. The objective of this research project is to examine the feasibility of using the major secreted proteins of F. tularensis in a subunit vaccine against tularemia. Such a vaccine would almost certainly be safer than the LVS vaccine and hopefully of equal or greater potency. The specific aims of this proposal are: (1) to identify proteins (by 1- and 2-dimensional gel electrophoresis) released extracellularly by F. tularensis growing in broth culture; (2) to determine (by immunoelectron micrscopy) if the major proteins released by F. tularensis into broth culture are also released in infected host cells; (3) to determine whether infection of mice with fully virulent or LVS F. tularensis induces a cell-mediated immune response (manifest by cutaneous delayed type hypersensitivity and by lymphocyte proliferation) against the major secreted proteins of F. tularensis; (4) to determine whether vaccination of mice with major secretory proteins of F. tularensis induces protective immunity against an otherwise lethal aerosol challenge; and (5) to determine whether addition of IL-2, IL-12, or microencapsulation of the vaccine improves its effectiveness. The research outlined in this proposal will identify the secreted proteins of F. tularensis, will determine whether they play a role in protective immunity, and will lay the foundation for a safe and effective vaccine against tularemia.