Scientists clone a goat

Three female clones were produced from the same parent and all are said to be perfectly normal and healthy.

The first of the clones, called Mira, was born in October last year. The other two - twins also called Mira - were born a month later. The researchers say the goats are a significant scientific achievement and an important step forward in the use of farm animals to produce drugs.

The clones were designed to express a substance called recombinant human antithrombin III (rhAT) in their milk. This protein prevents blood from clotting.

High production

Some rhAT extracted from the milk of one of the clones is already being tested on human patients who are incapable of producing enough of the chemical in their own bodies. Without this drug, surgical procedures become particularly dangerous.

Although rhAT can be made from the plasma of donated blood, the quantities produced are relatively small.

The fear of contamination has also prompted scientists to look for an alternative source of the protein.

The use of animals to make such proteins is called "pharming" and is one of the main applications envisaged for cloning.

Until now, genetic engineering has relied on bacteria or very difficult tissue culture techniques to make medically-useful human proteins.

But some biological molecules such as rhAT III are so complex they can only be manufactured in higher organisms such as mammals.

The solution, according to scientists, is to engineer and copy animals that will express these complex proteins in large quantities in their milk. The animal-derived products are also free from some of infections that can taint their blood-derived equivalents.

"We got all of the rhAT III we needed for three phase-three clinical trials from three goats," says Dr Patricia Diamond from the Genzyme Transgenics Corporation in Massachusetts which produced the clones.

The company says rhAT III is the first transgenically-produced protein to be introduced in human clinical trials and progress to such an advanced stage.

Goat embryo

Mira and her sisters were made using a variation on the nuclear transfer technique that produced Dolly the Sheep, the first mammal cloned from an adult cell.

In this case, the researchers took genetic material from a 40-day-old goat embryo which carried the transgene that expressed rhAT III. This was then fused with an empty egg taken from another goat and activated to make it think it had been fertilised.

The dividing and growing egg was then carried to term by a surrogate mother. The research team used 285 eggs to get the three live clones.

The research, conducted by a team from Genzyme Transgenics, Tufts University School of Veterinary Medicine and Louisiana State University, is published in the journal Nature Biotechnology.