Malaria vaccine produces protective antibodies in humans
Half of the human population live at risk from malaria infection. In 2015 there were 214 million cases and up to half a million people died from the disease.
Efforts to halt the spread of the parasitic disease, which is transmitted by mosquitoes, are being frustrated by rising levels of drug and insecticide resistance in malaria endemic areas. Now scientists have a potential new weapon to test in the form of a weakened strain of malaria that can safely be injected into susceptible humans to produce protective antibodies.
University of Washington researcher James Kublin and his colleagues, writing in Science Translational Medicine, have developed what they dub a GAP - genetically attentuated parasite - comprising a heavily disabled form of malaria from which they have deleted three key genes, p52, p36 and sap1.
Without these genes the parasite cannot complete its lifecycle and hence cannot cause disease. Critically it does still stimulate a powerful immune response, leading to protection for the recipient.
To test the new vaccine, the team first administered it to mice, which were rendered completely invulnerable to malaria for at least 6 months.
Next, the researchers tested the vaccine on a group of healthy human volunteers aged 18 to 50. Unfortunately the only way to administer the parasite is via mosquito bite, so the volunteers had to submit their forearms to a hoard of 150-200 hungry mosquitoes over a 10 minute period.
Within a month, the volunteers had developed very high levels of antibodies against the outer coat of the malaria parasite. These blocked infection of blood cells in a dish, proving that they were functional, and, transferred into mice could cut down the growth of the parasite in infected animals by up to 90%.
The team acknowledge that their vaccine candidate is limited by the necessity to administer it via the bite of a mosquito, but the results are extremely encouraging as researchers move towards a solution to what is the world's largest disease threat.