This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The complexity of the malaria parasite life cycle and the poor efficacy reported for vaccines candidates that have reached Phase 2 of clinical development has encouraged the search of alternative methodologies to elicit protective immunity. We have designed and expressed several pre-erythrocytic and erythrocytic chimeric recombinant proteins in the search of an optimal formulation capable of inducing long-term protection against malaria. Proof of principle studies have been done in mice using the rodent malaria parasite model Plasmodium yoelii. Potency tests have confirmed that the chimeric protein is highly immunogenic and able to induce robust immune responses against different components of the chimera. Most relevantly, the vaccine construct confers protection at very low doses to both hyper-parasitemia and severe anemia after experimental challenge with P. yoelii sporozoites. Delay in the prepatent period and low parasite burden after experimental challenge suggested that both, anti-pre-erythrocytic immunity and anti-blood stage immunity played a role in protection. To evaluate the impact of antibodies in protection, passive immunization experiments were done using polyclonal antibodies elicited against the two major components of the chimeric protein. These comparative experiments confirmed that functional antibodies against the blood stage component are essential for protection. We also established that CD4+ but not CD8+ T cells are required. This is the first evidence that a multi-stage protein-based vaccine can elicit protective immunity in malaria. Experiments are in progress to design a chimeric vaccine that also incorporates a sexual stage vaccine component.
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