BOSTON--Cows have been cloned from fetal cells for the first time, researchers announced here today at the annual meeting of the International Embryo Transfer Society. The new procedure may lead to a cheap and easy way to create cow "drug factories" that reliably produce human proteins--such as albumin, which restores osmotic pressure after major blood loss--in their milk.
Scottish researchers took a similar approach to clone sheep that will produce in their milk human factor IX protein, which is used to treat hemophilia. The latest results show that "the phenomenon and the technology are not restricted to one species," says Kenneth Bondioli, a reproductive physiologist with Alexion, a biotech firm in New Haven, Connecticut. Until now, cows have been cloned almost exclusively from embryonic cells, which are difficult to maintain in the lab and are less amenable than fetal cells--which have not specialized into distinct organs--to genetic tinkering. That's why the new work, says Bondioli, is "highly significant."
A team led by animal scientists Steven Stice of Advanced Cell Technology Inc. and James Robl, an animal scientist at the University of Massachusetts, both in Amherst, added foreign DNA to lab-grown cow fetal cells. They selected cells that had taken up the DNA and placed them in contact with cow eggs whose nuclei had been removed. The researchers zapped each egg and fetal cell with electricity to get them to fuse, then added a chemical mixture that inhibits enzyme activity to jump-start the biochemical machinery that produces an embryo. A week later, they inserted viable embryos into surrogate mothers that carried the calves to term.
From this technique, the Amherst team produced George and Charlie, week-old calves whose cells all contain the added gene. Eventually, they plan to make transgenic cows whose milk contains human albumin. This protein produced in commercial quantities could be a big hit among hospitals: Albumin purified from cow's milk would be free of viruses or other infectious organisms that may hitch a ride with protein purified from human plasma, says Robl. A single cow could make 80 kilograms of albumin a year, he predicts. Several more cloned calves are about to be born. "The technique is repeatable and commercially viable," Robl says.