| Coccidioides is a primary fungal pathogen endemic to the alkaline desert soil of the Southwestern United States and the etiological agent of coccidioidomycosis (Valley fever), a respiratory disease in humans. Coccidioides represents the only fungal pathogen on the Center for Disease Control's select agent list of possible weapons of bioterrorism, and can cause significant morbidity in infected individuals. Thus, the need for a human vaccine against coccidioidomycosis has come to the forefront. Work has centered on identification and characterization of recombinant T cell-reactive antigens, because clinical and experimental data suggest that activation of a durable MHC II restricted T cell Th1 immune response is of principal importance in establishing durable protective immunity. Immunoprotection experiments in mice using single recombinant vaccine proteins of Coccidioides have resulted in less than optimal survival and clearance of the fungus from the infected host compared to whole cell or multicomponent subcellular vaccines, indicating a lack of protective epitopes in the single protein vaccines. Therefore, it is likely that a protective recombinant protein subunit human vaccine against Coccidioides will contain genetically unrestricted ("promiscuous") protective T cell epitopes, and will most likely be multivalent in nature. In this study we describe an immunoproteomic and bioinformatic approach for profiling a diverse immunogenic protein component of the coccidioidal parasitic cell wall. A phospholipase B (Plb), alpha-mannosidase (Amn1), and an aspartyl protease (Pep1) were selected as candidate vaccine proteins on the basis of their immunogenicity, cellular localization, predicted promiscuous T cell epitope content, and T cell reactivity. These antigens were evaluated individually, and in combination, for their protective efficacy in a pulmonary murine model of infection. Each individual protein showed significant protection in infected mice as evaluated by survival after lethal challenge (53%-61% survival). A combinatorial vaccine composed of all three protective antigens enhanced survival in infected mice (86% survival) and significantly improved clearance of the pathogen from lungs of surviving mice by 90 d post-challenge. This strategy has been successful in producing the most comprehensive profile of immunogenic coccidioidal cell wall antigens to date, and lays the groundwork for the development of an epitope-driven, multivalent human vaccine against coccidioidomycosis. |
