Malaria finding points to possible new vaccine

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By Kate Kelland
LONDON (Reuters) - A vaccine or new drugs against malaria could be developed, British scientists said, after they made a critical discovery about the way the most deadly species of malaria parasite invades human red blood cells.

Researchers from the Sanger Institute pinpointed a single receptor for a protein that is critical for the parasite to gain entry into red blood cells before multiplying and spreading.

Blocking it could halt the killer disease in its tracks and may prove a good way to design a vaccine, they said, although this could take another decade or so to become a reality.

"Our research seems to have revealed an Achilles heel in the way the parasite invades our red blood cells," said Gavin Wright who co-led the study published in the journal Nature on Wednesday. "Our findings were unexpected and completely changed the way in which we view the invasion process.

"The great hope is that this breakthrough will facilitate the path toward a more effective vaccine," he told reporters at a briefing in London.

Malaria is a mosquito-borne parasitic disease that kills around 800,000 people a year, the vast majority of them children under the age of five in sub-Saharan Africa.

The blood stage of the parasite's life cycle begins when it invades human red blood cells, and it is this stage that is responsible for malaria illnesses and deaths.

Scientists have been working for decades on trying to develop an effective vaccine against the disease, but this has proved particularly tricky.

British drugmaker GlaxoSmithKline published data last month showing its experimental RTS,S vaccine halved the risk of children getting malaria in a large trial in Africa, making it likely to become the world's first licensed malaria vaccine and also the first against a parasitic disease.

Other teams of researchers around the world are also working on other approaches to a malaria vaccine.
Experts agree wiping out the disease -- a goal the scientific community says could be achieved in the next few decades with the right tools -- will take a vaccine that is far more effective than RTS,S, which had a success rate of around 50 percent in trials.

"(The) positive results from ongoing malaria vaccine trials in Africa are encouraging, but in the future more effective vaccines will be needed," said Adrian Hill, a senior investigator at Oxford University's Jenner Institute.

"The discovery of a single receptor that can be targeted to stop the parasite infecting red blood cells offers the hope of a far more effective solution."

Using new technology called an Avidity-based Extracellular Interaction Screen (AVEXIS) developed by Wright's team, the British scientists uncovered a vital interaction between a malaria parasite protein called PfRh5 and a receptor in the host -- the human red blood cells -- called basigin.

"Once we'd identified this, the key question was did it have anything to do with how the parasite gets inside the red blood cell," Julian Rayner, also from the Sanger Institute and who worked on the study, explained at the briefing.

The research team tried to block the interaction in cultures of the parasites growing in red blood cells in the lab, and found that with an antibody they were able to halt completely the parasites' ability to invade the cells.

"Using antibodies targeting this interaction we could essentially stop all invasion of red blood cells," Rayner said. This bodes well for the potential efficacy of a future vaccine developed using this technique, he added.
(Editing by Robert Woodward)

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