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Genetically Engineered Malaria Parasites May Help Prevent Infection in Humans

Using genetically engineered live Plasmodium falciparum parasites, a team led by scientists from the University of Washington have developed a malaria vaccine that appears to protect healthy individuals against the disease for at least a month. The work, which is described in this week's Science Translational Medicine, may lead to the development of an effective attenuated malaria vaccine. The scientists previously developed a genetically attenuated strain of P. falciparum — called PfGAP3KO — and showed its safety and immunogenicity in humans. In the latest study, the group tested whether a vaccine based on PfGAP3KO could prevent controlled malaria infection in people. The vaccine was given to 16 healthy volunteers as either three or five immunizations administered via mosquitos infected with PfGAP3KO. The vaccine was well-tolerated, with minimal side effects and no breakthrough infections. A month after the final immunization, the volunteers were exposed to bites from mosquitos with fully infectious P. falciparum. Half of the study participants showed no evidence of the parasite's RNA in their blood after 28 days and one participant showed complete protection when they were exposed to the parasite six months later. The results, the study's authors write, establish a proof of concept for the vaccination strategy and support further evaluation in dose range-finding studies with an injectable formulation.