Scientists from the US genetically engineered the plasmodium parasite that causes the disease, after being passed on from mosquitos, to remove three genes that lead to infection. Although they can’t multiply , they live in the liver and stimulate the body’s defences to repel a real infection.
Plasmodium parasites first infect the liver and then blood, leading to more than 200 million infections and nearly half a million deaths worldwide in 2015. “The most clinically advanced vaccine in development contains fragments of the malaria parasite and is only partially protective,” said James Kublin from University of Washington.
Vaccination with whole, live-attenuated parasites offers an alternate approach, but its potential to cause breakthrough malaria infection poses formidable safety challenges. To overcome these hurdles, researchers created genetically attenuated parasites (GAP) by knocking out three genes (GAP3KO) in plasmodium falciparum that arrested its development within the liver, thereby preventing its advance to blood infection, the stage of malaria that triggers disease symptoms.
The GAP3KO vaccine was administered through infected mosquito bites in a controlled setting. The participants during the human trial, none of whom developed malaria symptoms or signs of infection in the blood, showed strong protective antibody responses, researchers said. When transferred into humanised mice, these antibodies blocked malaria infection in the liver. These promising results pave the way to phase 1b trial of GAP3KO vaccine.
Doctor Sebastian Mikolajczak, Centre for Infectious Disease Research scientist, said, “The clinical study now shows that the GAP3KO vaccine is completely attenuated in humans and also shows that even after only a single administration, it elicits a robust immune response against the malaria parasite.”