Pre-erythrocytic vaccine antigen (PEVA) candidates are transcribed during liver stage (LS) development. PEVA immunogens are recognized by CD8+ and CD4+ T cells in protected rodents and naturally exposed humans. The LMIV Pathogenesis and Immunity Section and SBRI have assessed the protective efficacy of some of these immunogens after DNA vaccination in rodent models of malaria. Our next objective is to establish the nonhuman primate and human models of protective pre-erythocytic immunity for further studies, to identify additional antigens that may be contributing to protective pre-erythrocytic immunity, and to assess the efficacy of leading immunogens in animals models that can guide the prioritization of those antigens to be tested in humans. During the past fiscal year, LMIV scientists have accomplished the following: 1. Completed pilot studies of nonhuman primate models of pre-erythrocytic malaria immunity, using whole organism and subunit vaccine strategies. We have determined that rhesus monkeys can be protected against P. knowlesi infection by whole organism vaccination, and also that CD8 T cell responses against 2 of our novel PEVA antigens are associated with reduced blood stage burden of malaria after sporozoite challenge. 2. Identified 2 additional candidate pre-erythrocytic antigens that confer protection against liver stage malaria in rodent models. 3. Determined that naturally exposed African children who develop CD8 T cell interferon gamma responses against leading PEVA antigens, demonstrate reduced risk of malaria infection during followup. This observation is being confirmed in another season of followup. 4. Established a flow cytometry based method to measure the effect of antibodies to block malaria parasites from infecting liver cells.
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