FEATURE - World's worst diseases face new foe - biotechnology
Date: 12-Nov-01
Country: UK
Author: Jeremy Smith
By using biotechnology to incorporate useful genes into an almost limitless variety of common plants, from rapeseed and tobacco to potato, tomato and banana, scientists aim to produce cheap and stable vaccines in an edible form - and beat disease.
Scourges such as cholera, tuberculosis and hepatitis, all responsible for the deaths of millions every year including many children in developing countries, have been targeted as candidates for vaccines which can be engineered from plants.
And in another use of biotechnology, there is now some realistic hope that mankind's centuries-old battle against malaria may soon be nearing its end due to a breakthrough last year in producing the world's first transgenic mosquito.
So far, there seems to be no obvious end to the sheer variety of biotechnology's potential applications in the fight against disease. Even the roots of the humble tobacco plant are being used to mass-produce a vaccine against scorpion stings in Brazil, which may eventually be incorporated into fruit.
"It's a relatively recent technology and I don't know when we would ever see commercially available vaccines. But it's quite exciting," said Mike Steward, immunologist at the London School of Hygiene and Tropical Medicine (LSHTM).
"It doesn't matter in what plant you insert them (genes) as the molecular biology principles are identical. The versatility is amazing," he said.
Genetic modification (GM) involves exchanging or splicing genes of unrelated species that cannot naturally swap with each other, and the species can be as different as chalk and cheese.
Scientists have spliced spider venom genes into maize and other food crops as a 'natural pesticide' to deter insects and birds from feeding on the plants, and inserted fish antifreeze genes into tomatoes to extend their growing season into winter.
VACCINES FIND NEW HOME IN VARIETY OF COMMON FOODS
The first human clinical trial of an edible vaccine took place in 1997 when volunteers ate raw potatoes which were genetically engineered against the common E. coli bacteria.
Since then a whole range of plants, most often vegetables, has come under the bioscientist's knife for adaptation as a possible host for vaccines. Foods under study include bananas, potatoes, tomatoes, lettuce, rice, wheat, soybeans and corn.
"One day children may get immunised by munching on foods instead of enduring shots. More important, food vaccines might save millions who now die for lack of access to traditional innoculants," said leading journal Scientific American in an article last year on edible vaccines.
"The advantages would be enormous," the article said. "Nothing would be more satisfying than to protect the health of many millions of now defenceless children around the globe."
Last year, the spotlight fell on hepatitis B, a virus which can cause high fever, lifelong infection, cirrhosis of the liver and liver cancer. More than 60 percent of liver cancers worldwide have been linked to hepatitis B.
Mice were fed with modified potato, containing an oral vaccine for hepatitis B which passed through the animals' stomachs without being broken down and stimulated the production of antibodies against the disease.
Scientists now say tomatoes and bananas genetically modified to contain such a vaccine may be able to eradicate the virus.
Clinical trials have been conducted on pigs using an edible vaccine for transmissible gastro-enteritis in corn, while work is continuing on a vaccine using tomatoes for RSV, a respiratory virus which can be fatal for infants less than six months old.
One recent offbeat development was the isolation in a British laboratory of a non-toxic protein within the venom of a tiny yellow scorpion which is common in parts of Brazil.
When injected into animals, the protein proved to be a good potential vaccine as it set up a strong immunity to the venom. But the problem was that only very limited amounts of the protein could
