The human gene harvest

Tobacco plants containing human genes have been grown in the US

By BBC News Online's Helen Briggs

Rows of tobacco plants grow in a remote field in Virginia, United States.

Although they look like any other crop, these plants, which contain a human gene, represent the future hopes of the biotech industry.

We had human serum albumin and another human protein growing in seven different sites in the state of Virginia in the field last summer

Carole Kramer, Chief Scientific Officer, CropTech

CropTech Corporation, a company trying to turn plants into medicine factories, believes that tobacco plants like these, tested in field trials last summer, will one day be able to manufacture human proteins capable of treating a host of diseases.

But the research has triggered debate among those opposed to the transplant of human genes into plants, including the Catholic Church.

GM first

Tobacco was the first plant ever to be genetically modified, back in the 1980s. The easiest plant to genetically engineer, it is a rapid and efficient biomass producer.

"Tobacco has a great reproductive rate and so a single plant will produce up to a million seeds," says Professor Carole Cramer, Chief Scientific Officer at CropTech and a professor at Virginia Tech. "If you compare that say with corn - a single corn plant will produce maybe 300 seeds.

Infants with rare genetic diseases could one day be treated with medicines made by plants

She says that, in many cases, plants will be able to make drugs that no other system can make.

"In a situation where medical costs are escalating at such a rate if we can actually come up with technologies that bring the forefront of science, the new medicines that are available, to people in a cost-effective way, that is significant."

CropTech, based in Blacksburg, Virginia, has already inserted nine different human genes into tobacco. It is also testing proteins from a number of other biotech and pharmaceutical companies to see whether plants can be persuaded to synthesise these potential drugs.

Enzyme factory

One example of a human protein that has been successfully expressed in tobacco plants, albeit in small quantities, is the human enzyme glucocerebroside, which processes an essential fatty substance in the body.

If the enzyme is absent, because of a genetic mutation, the fat builds up in the organs and sometimes brains of newborn babies. The result is a rare genetic disorder known as Gaucher's disease, which, in the most severe cases, is fatal by the age of six months.

Plants may be able to produce blood products

Gaucher's disease can be treated - by replacing the missing enzyme - but the treatment is very expensive and must be taken for life.

Until recently, the enzyme replacement therapy used to treat Gaucher's disease, with an average price per patient of more than $150,000 (£104,000) a year, was known as the "most expensive drug in the world".

The drug had to be laboriously extracted from human placenta, a single dose requiring 400-2,000 of them.

Last year, a new drug, manufactured in a mammalian cell culture system, came on to the market. Although the drug is regarded as safer, it is no cheaper, which is why CropTech is trying to produce the drug in tobacco.

Clinical trials

Professor Cramer says the best tobacco plants are able to synthesise a single dose of active enzyme - but not in the exact form needed for human metabolism.

"This has not moved into human clinical trials because for this particular enzyme the exact shape of the sugars on the outside are critical for it to function appropriately in the human body and tobacco doesn't do that quite right," she says.

CropTech is also working on producing blood clotting replacement products such as human serum albumin in bioengineered plants. The first generation of tobacco plants made human serum albumin but not in commercially useful quantities.

"We had human serum albumin and another human protein [a clot bluster, a blood protein] growing in seven different sites in the state of Virginia in the field last summer," says Professor Cramer.

"The time at which it will make a real difference is when it becomes an actual product and because these are pharmaceuticals they have to go through full clinical trials," Professor Cramer adds.

Triggered debate

However, scientists acknowledge that it will be at least 10 or 20 years, if ever, before so-called 'pharma' factories might become a reality.

And the idea of putting human genes into crops has triggered debate in the Catholic Church.

"The Vatican has given a cautious welcome to genetic engineering," said Denise Calder, secretary for environmental justice to the Bishop's Conference of England and Wales.

"They're not against genetically modified organisms generally, but I'm sure they would be concerned about using human genes."