Edible vaccine for malaria on way
Bangalore: A spoonful of genetically modified starch could be a new malaria vaccine if a new strategy that seems to work in mice also performs well in humans.
At present there is no efficient vaccine against malaria, which is caused by the plasmodium parasite. Now researchers from two laboratories in France have successfully vaccinated and protected mice using a new strategy they developed.
A team of researchers from the University of Science and Technology at Lille in France and the National Institutes of Health in the United States have demonstrated in animals their vaccine strategy based on the ingestion of genetically modified starch.
They protected the mice from malaria by feeding them starch derived from a green algae called chlamydomonas reinhardtii that was genetically modified to carry the vaccine proteins (antigens) that will elicit antibodies against the malaria parasite.
Reporting online in the scientific journal PloS One, they say their findings on the use of the recombinant anti-malaria vaccine open up a new method for a simple and safe vaccination for children at risk. According to the WHO, every year malaria kills one million people, mostly young children.
Although this is "an interesting concept", edible vaccines in general have not taken off for a variety of reasons, Govindarajan Padmanabhan, a leading biochemist and a malaria researcher at the Indian Institute of Science in Bangalore told.
"All antigens do not work through the oral route," he said, adding that there is also the problem of adjusting dose and schedule in an edible product, unlike the conventional vaccine, which is directly injected into blood in a defined concentration and dosage.
"Nevertheless, it would be interesting to see whether a proof of principle can be obtained (with the edible malaria vaccine) in the human," Padmanabhan said.
For their animal experiments, the researchers used three distinct plasmodium antigens that have shown their efficacy in "conventional" vaccinations as vaccine candidates against malaria.
They fused these antigens to an enzyme called GBSS in starch grains purified from the green algae through genetic engineering. These "modified" starch grains were then fed to the mice that had been previously challenged with a lethal dose of a malaria parasite called plasmodium berghei. The researchers showed that the mice vaccinated by these starch grains were protected from malaria.
They said the animal vaccine studies suggested that the levels of transgenic starch antigens used were "sufficient to confer substantial protection against lethal plasmodium berghei in mice".
Additionally, in test-tube studies, they showed that the transgenic starch elicited antibodies to plasmodium falciparum, another parasite that causes cerebral malaria.
The algae C. reinhardtii thus provides an ideal expression system for the production of recombinant vaccine, the scientists reported. "Aside from the tremendous advantage of producing clinically relevant antigens in starch, transgenic algae can also be generated quickly," they said.
The algae can be grown on scales ranging from a few millilitres to 500,000 litres and the starch grain can easily be produced from the plant extract and purified in large quantities, they reported.
Satisfied with animal studies the researchers now plan to test the efficacy of various plasmodium antigens and find out if their recombinant anti-malaria vaccines in starch, derived from the algae, can be applied to humans.
According to the researchers, the starch of edible plants could also be transformed in the same way as that of the algae C. reinhardtii. They are therefore also examining the possibility of using starch from crop plants including cereals and potatoes.
Administered to children such edible plants could be both a food source and a vaccine, they claim. This strategy would allow simple vaccination and avoid storage problems (as starch has long shelf life) and syringes.
In conclusion, the scientists said "this novel system paves the way for efficient production of edible vaccines that can be genetically produced in Chlamydomonas".