Scientists to stop GM pigs research over virus fears

The scientists who created Dolly the cloned sheep will halt experiments with genetically modified (GM) pigs to produce organs for human transplants, because of concern that they could produce deadly new diseases.

The scientists who created Dolly the cloned sheep will halt experiments with genetically modified (GM) pigs to produce organs for human transplants, because of concern that they could produce deadly new diseases.

The decision follows mounting independent evidence that pigs' DNA contains HIV-like "retroviruses" which, while harmless to the animals, could have unpredictable effects if let loose in a human host.

Geron Bio-Med, the Californian company which has exclusive rights to the cloning technology developed at the Roslin Institute near Edinburgh - has halted funding partly due to the fears. Geron last year took over the institute, now called Roslin Bio-Med. The company has decided it would be impossible to identify every retrovirus in pig DNA.

Ian Wilmut, the leader of the team which created Dolly, said he was disappointed by the move, which comes as the Government prepares to allow limited trials of pig organ transplants in to humans. This process is known as xenotransplantation. A moratorium was placed on such transplants in 1997 when retroviruses were discovered.

Pigs' biology and size is surprisingly close to humans', making them potentially attractive organ donors. But now the work is in limbo, and could collapse completely.

"We are in the process of reducing pig work," Professor Wilmut said. "It has not quite finished but it will be before long. There is a certain reduction in the optimism of how practical it will be to take animals and use them in this way."

He said that the decision was disappointing: "I think the concern is mainly unknown viruses. That's the frightening thing. If you know what the disease is you know how to look for it."

However, the Government is also expected this week to announce a limited go-ahead for the cloning of "stem cells" from human embryos. If successful, that method could lead to the creation of organs for transplant involving entirely human DNA, and so avoid the problems associated with pig organs.