Genetically engineered pigs are yielding bounteous supplies of milk loaded with a human protein that prevents blood clotting, a promising advance in the quest for valuable pharmaceuticals to treat human disorders, scientists reported.
The first transgenic pig is a 275-pound sow named Genie who was born a year ago. She and her sisters already have given birth to 28 piglets, all carrying the same gene for the important protein, said William Velander of Virginia Polytechnic Institute in Blacksburg, Va.
The creation of these otherwise normal and healthy animals through biotechnology, Velander said, offers the prospect of large-scale production of many different human proteins.
The anti-clotting substance derived from the first generation of pigs already is undergoing preliminary trials in humans, said Velander, expressing optimism that the newly endowed genetic trait will be carried on in future transgenic pig generations.
Velander described his group`s work on Monday and will present a formal paper at the national meeting of the American Chemical Society in San Francisco.
Genie`s life began after the Virginia scientists injected two foreign genes into a single fertilized pig egg in the laboratory and then transferred the genetically altered embryo into the womb of a surrogate mother that carried the animal to term.
One of the two genes came from human liver and carried the genetic code instructing the altered pig to produce an exceedingly complex human substance called Protein C, a powerful anti-clotting agent. The other gene came from a mouse and acted as a switch to turn on the Protein C gene when the pig was old enough to produce milk.
To Velander, the great advantage of using genetically engineered pigs to produce Protein C and other valuable human therapeutic proteins is the fact that the animals mature within a year, produce large litters of up to a dozen piglets twice a year, and can be milked easily many times a day.
The 28 piglets that Genie and her six sisters have borne all carry the Protein C gene, Velander said. The research team is enthusiastically testing the next generation to make sure their milk also yields large quantities of the valuable protein.
The Virginia researchers, by transferring their methods to biotechnology companies and commercial pig breeders, will originate a race of transgenic pigs whose yield of the protein will far surpass the quantities now obtained from limited supplies of human blood and plasma, Velander said.
Human Protein C alone, he said, can be used to prevent blood clotting in patients who have had heart attacks and who are in danger of forming deadly clots after their first clots have been dissolved by such drugs as
streptokinase or the genetically engineered compound TPA.
Copious and cheap supplies of the protein from transgenic pig milk also should prove valuable in treating such problems as toxic shock, pulmonary embolisms and the formation of clots after hip replacement surgery, Velander said.
The science of creating transgenic animals has been developing since 1984, when Richard Palmiter of the University of Washington and Ralph Brinster of the University of Pennsylvania created the first transgenic mice by endowing mouse embryos with the genes for rat growth hormone.
The resulting supermice, twice the size of the ordinary variety, brought a whole new understanding of the genetics of growth regulation.
Since then, transgenic animals have become a standard tool in genetics and disease research, and today animal scientists are seeking to use transgenic cows, sheep and goats to produce usable quantities of many hormones and proteins.
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