SciDev.Net

Malaria parasite in human blood: the vaccine targets this stage of the parasite's life cycle, the schizont

IRD / Frézil

Researchers have reported promising results from the first human trials of a malaria vaccine that mimics the natural immunity some people develop against the disease.

If successful, the vaccine would provide much-needed protection against the disease, which kills up to three million people a year.

The team led by Pierre Druilhe at the Pasteur Institute in France published their results in PLoS Medicine yesterday (7 November).

Despite decades of effort, scientists have failed to make a malaria vaccine that works. The main reason is that once inside the human body, the parasite changes form several times.

Vaccines usually work by stimulating the human immune system to make proteins called antibodies that attack other proteins on infectious organisms called antigens.

Although the malaria parasite has several antigens that a vaccine could target, they vary depending on what stage the parasite is at in its life cycle. This means that a vaccine might not work against all strains of the parasite.

Druilhe and colleagues developed their vaccine against a protein (MSP3) made by the form of the parasite that enters human red blood cells — the most damaging stage of its life cycle.

This is also the form of the parasite that some people who are regularly exposed to the parasite develop immunity to.

When the team tested the vaccine on 30 healthy people who had never had malaria, 23 of them produced antibodies in response.

The researchers showed in laboratory tests that these antibodies helped to destroy the parasite.

For ethical reasons, the team could not infect the volunteers with malaria to see if the vaccine worked in people, but they now plan to test the vaccine in Burkina Faso on people who are already at risk from malaria.

Druilhe told SciDev.Net that the fact that antibodies remain in the human body for nearly a year was "unusual and good news".

Given other scientists' failures to make an effective malaria vaccine, the team are cautious about their success.

But, says Druilhe, the prospects for their vaccine are "much better" than for other candidate vaccines targeting malaria at the same stage of its life cycle.

"We have a strong biological activity against the parasite that has not been found with other vaccines". 

Link to full paper in PLoS Medicine

Reference: PLoS Medicine 2, e344 (2005)