The British scientists who cloned Dolly the sheep said yesterday they had made a major advance by cloning Polly the lamb, which carries human genes. This means they can clone herds of identical sheep that produce human proteins or blood products for medical use.
Polly and four near-identical sisters are transgenic - they are sheep but they carry a human gene. "It was what we told everybody we were going to do, but it's nice to be able to say we have done it," said Mr Ron James, managing director of PPL Therapeutics plc.
"This is a demonstration that we can genetically modify the cells and then make transgenic animals, which is a world first."
PPL's scientists have cloned sheep before - not only Dolly but nine others using other techniques. They have also created many transgenic animals - one at a time. This is the first time they have been able to combine the two technologies.
The five Polly Dorset lambs were not using the stunning technology that produced Dolly.
Dolly was the first mammal cloned from an adult cell. Polly and her virtually identical sisters were created by fusing a fibroblast cell from a foetus to an egg cell.
It is slightly easier to use embryonic cells to make clones, as they still have the natural potential to grown into complete animals, rather than into skin cells or brain cells or muscle cells.
What is different this time is that the PPL team genetically modified the foetal cells before they cloned them.
Two of the five lambs have so-called marker genes, which are easy for scientists to find and verify in the animal.
"Three of them are carrying a human gene of therapeutic value. I'm not going to say what it is," Mr James said.
The company's sheep produce alpha-1-antitrypsin, a blood protein used to treat the symptoms of cystic fibrosis.
They also have been genetically engineered to produce fibrinogen, factor VII
and factor IX - all blood-clotting products and activated protein C, which prevents clotting.
The five lambs, all born within the past month to different mothers, did not come from the Scottish-based company's scrapie-free herd, so they will not produce any commercial products, Mr James said.
Instead, they will be monitored and scientists will try to duplicate the technique in sheep guaranteed free of the brain-wasting disease.
Although the transgenic technology works, it is hit-and-miss. Sometimes the genes "take" in an animal and sometimes they do not. The idea behind cloning transgenic animals is to guarantee that the genes are there and the animal will produce the desired human protein.
But Mr James said the company did not intend to produce herds of clones.