Immune children raise hopes of malaria vaccine breakthrough
Researchers’ discovery of an antibody that halts the progress of malaria by caging its parasites in red blood cells, has raised fresh hopes of a vaccine against a disease that kills more than 600,000 people a year.
The team of scientists, led by Jonathan Kurtis of Rhode Island hospital’s centre for international health research, found the antibody while investigating why 6% of a group of 785 Tanzanian children possessed natural protection against malaria.
Using blood samples and epidemiological data collected from the children, the researchers pinpointed a protein, known as PfSEA-1, which the parasites need in order to escape from inside red blood cells they infect as they cause malaria. They realised that the immune children were producing an antibody that locked PfSEA-1 into their red blood cells, stopping its spread.
Kurtis said: “Many researchers are trying to find ways to develop a malaria vaccine by preventing the parasite from entering the red blood cell, and here we found a way to block it from leaving the cell once it has entered. If it’s trapped in the red blood cell, it can’t go anywhere – it can’t do any further damage.”
Although the potential vaccine has yet to be tested on humans, trials on mice have yielded encouraging results. Despite being infected with a deadly form of malaria, the vaccinated rodents lived almost twice as long as unvaccinated ones and had far lower levels of malaria parasites.
The vaccine will be tested on monkeys in the next month, and if the trial is successful, a clinical trial testing the vaccine in a small group of people could begin within 18 months.
The research, published in the Science journal, could lead to the development of a vaccine that would prevent the progression of plasmodium falciparum malaria, which kills one child every 15 seconds in Africa and south-east Asia annually.
Our findings support PfSEA-1 as a potential vaccine candidate, Kurtis added.
We are confident that by partnering with our colleagues at the National Institutes of Health and other researchers focused on vaccines to prevent the parasites from entering red blood cells, we can approach the parasite from all angles, which could help us develop a truly effective vaccine to prevent this infectious disease that kills millions of children every year.
Scientists work on malaria treatments at the University of Cape Town’s drug discovery and development centre laboratory. Photograph: Nic Bothma/EPA
Microscopic malaria parasites are carried in the saliva of female mosquitoes and enter a person’s bloodstream through the insect’s bite. The parasites pass through the liver and infect red blood cells. They replicate wildly in these cells and cause them to rupture, flooding the body with more parasites.
Two existing approaches to vaccine development have sought to block the parasites from entering the liver or red blood cells. The new approach tries to bottle them up inside the red blood cells or, as Kurtis described it, “trap them inside a burning house”.
If the parasites remain trapped, they can be harmlessly gobbled up in the spleen by immune system cells called macrophages, Kurtis said.
David Lanar, a parasitologist at the Walter Reed Army Institute of Research in Silver Spring, Maryland, described the research as a “very elegant approach” to fighting malaria. He said that while the possible vaccine would not prevent infection, it would help reduce the symptoms of malaria.
“At this stage of the game, that’s a good thing,” he told Science. “The number of parasites in your blood determines how sick you will be.”
Annemarie Meyer, director of advocacy and programmes at Malaria No More UK, welcomed the news but stressed that the potential vaccine was still at a very preliminary stage.
“This is an exciting new target, but it’s very early,” she said. “Even in the best case scenario, we are looking at about a decade of testing and development before we could see this vaccine in use.”
According to the World Health Organisation, malaria killed 627, 000 people in 2012 – most of them children in sub-Saharan Africa.
Another malaria vaccine could be introduced in the world’s worst affected countries next year, after the latest trial of a treatment produced by Britain’s biggest drug company reduced the number of cases of the disease experienced by babies.
The results of trials in October 2013 showed that the RTS,S vaccine developed by GlaxoSmithKline nearly halved the cases of malaria experienced by children aged between five and seven months and cut the number of cases in babies aged six to 12 weeks by a quarter.