Health: An unnatural harvest

Anxieties about GM foods may soon be overridden by GM cures.

The potatoes being fed and watered in a corner of a Cambridge laboratory are about to provide a bumper harvest. Nearly 2ft tall, and lush and green, with an abundance of tubers, the plants look like the run-of-the-mill Desiree potatoes that grow in thousands of back gardens and allotments across the country.

But these potatoes will never be boiled, roasted or fried, and in six months' time genetically changed tubers just like them will be eaten raw by a group of patients to give them protection against hepatitis B.

Several thousand miles away, in Mountain View, California, tobacco plants are producing a compound that's already being used to stop tooth decay in 100 or so volunteer patients in London. And in Wisconsin, 10 acres of genetically altered maize are being harvested not for food, but for an anti-cancer drug.

Crops like these are in the vanguard of the burgeoning health science of growing medicines and vaccines in plants by transplanting human genes or bits of viruses into them.

While controversy rages in Britain about the safety of genetically modified plants for eating, scores of other GM plants are already being developed to create products to prevent disease, cure illness and save lives. Biotech companies are growing drugs in transgenic plants such as soya and maize to provide treatments for conditions as diverse as cancer the common cold, herpes, traveller's diarrhoea, stomach ulcers, cholera and hepatitis. Also being grown is a therapy to mop up the physiological effects of drug overdoses, and one group of researchers is looking at growing a new type of contraceptive pill in the tobacco plant.

The biotech companies claim that growing medicines like this is the way forward. It is relatively cheap, mass production is easy, quality control is assured, and infection risks are almost zero. Plant vaccines are eaten rather than injected, and they don't need to be kept refrigerated - a major advantage for preventive health care in the Third World.

"Supply is not a problem. If you want more medicine you just go out and plant a few more acres of corn or soya bean or whatever you are using," says Dr Vikram Paradkar, who supervises several acres of anti-cancer maize on the plains of Wisconsin.

The technology behind this revolution in health care is relatively straightforward. Many transgenic plants have been engineered to produce antibodies to disease. Our bodies naturally produce antibodies in response to attack by viruses or bacteria, but in some situations the infection is overwhelming, or the body may be unable to recognise the invader as a danger.

What many biotech companies have done is to take a piece of human DNA carrying the genetic instructions for making a particular antibody and insert it into the cells of a plant. It becomes part of the DNA, which then gives instructions to the plant to grow the human antibody in its cells as if it were its own. It can then be harvested and turned into a tablet or capsule.

At Planet Biotechnology in Mountain View, for example, the DNA that codes for the production of an antibody that prevents tooth decay is put on to a tiny tungsten bullet and blasted with a high-pressure gun into the nucleus of tobacco plant cells. Transgenic plants are then grown, which produce large amounts of the human antibody for tooth decay.

Dr Julian Marr, senior lecturer and consultant at St Thomas' and Guy's Dental Hospital, who identified the antibody and worked with Planet on producing it in plants, says, "Four per cent of the population don't get tooth decay because they naturally have this antibody, but in the other 96 per cent the antibody response is not good enough to be effective... What we have been able to do is to get the tobacco plants to make large amounts of the antibody we are using on human trials both here and in America. We have a second trial in London starting later this year. Our earlier results on 100 or so patients have shown that when the antibody goes into the mouth as a wash or as a toothpaste it provides protection for up to 12 months against the bacteria that cause decay."

A similar production approach is being taken by Dr Paradkar, with the growing of anti-cancer antibodies in his transgenic maize. It's estimated that each acre planted will produce enough of the drug for about 2,000 patients, and clinical trials have already begun in America.

The idea with this antibody is that it identifies tumour cells and sticks to them, allowing delivery of targeted radiation therapy to try to kill them off. It's expected to be especially useful in dealing with cancers that have spread too far to be cut out by surgery.

"The antibodies are being used as targeting agents to deliver toxins to knock out the cells... Chemotherapy and radiotherapy cannot distinguish between tumour and healthy cells, but this antibody sticks only to cancer cells," says Dr Paradkar.

In Britain, Axis Genetics in Cambridge leads the world in developing edible plant vaccines, including therapies for cancer, traveller's diarrhoea, cholera and hepatitis B.

Clinical trials on the Axis hepatitis B potato begin in America later this year, with about 20 patients. It may be given in raw potato form or made up into a tablet, and its success is measured by the levels of antibodies that are found in the blood of the volunteers before and after they eat it.

"There is a conventional hepatitis B vaccine available, but it is very expensive. Our production costs would be much lower, and swallowing a vaccine is always going to be more popular than having an injection. Because it doesn't need to be kept refrigerated, it could make big inroads into dealing with the hepatitis B problem throughout the Third World," says Axis's chief executive, Dr Iain Cubitt.

However, it is the tobacco plant that remains the most popular among biotechs. A group in California is looking at using the plant to grow antibodies that would block pregnancy and in effect act as contraceptive pills.

Twenty years ago, any idea that the much-maligned tobacco plant could be a force for good would have been treated with scepticism. It is now being used to make at least 12 compounds designed to fight disease. Perhaps the greatest irony of all is that researchers in Virginia are now looking to transgenic tobacco to provide effective treatment for lung cancer.