LONDON - PPL Therapeutics plc, of Edinburgh, Scotland, is looking for a partner to commercialize the blood-clotting agent Human Factor IX, after achieving an expression level of 300 mg/liter in the milk of transgenic sheep, which is a level never previously achieved, the company said.

A flock of 50 sheep could produce enough of the blood-clotting plasma protein to satisfy the £100 million world market, the company said.

Alan Colman, PPL's research director, said he was “very excited“ by the high production rate.

“Levels of Factor IX in human blood are very low - approximately 5 mg per liter - and the sheep have made 60-fold the natural circulating amount of this high-value protein,“ Colman said.

Inability to produce Factor IX is an X-linked trait that causes the rare form of hemophilia, hemophilia B, which occurs in one in 30,000 males.

The common form of hemophilia arises from an inability to produce the clotting agent Factor VIII. The world market for Factor VIII is estimated at about US$1 billion.

Currently, most Factor IX is derived from human plasma, rather than manufactured with recombinant technology. PPL says its transgenic Factor IX offers the advantages of low production cost and a consistent, high-quality product, with an improved safety profile. Because it can be guaranteed free of human viral contaminants, it could be used both therapeutically and preventively.

Last month, the U.K. government ordered the destruction of blood products derived from U.K. blood donations because of concern over possible contamination with the new variant of the neurological disorder Creutzfeldt-Jakob disease, believed to be caused by eating beef from cows with bovine spongiform encephalopathy (BSE, or “mad cow“ disease). There is no effective diagnostic test for prions, the infectious agents that cause the disease.

In the U.K. more than 3,000 people were estimated to have been infected with hepatitis C from blood transfusions before it became mandatory to screen donors for the virus in September 1991. More than 2 million people worldwide are estimated to have been infected with HIV through contaminated blood transfusions.

Ron James, managing director of PPL, said the company's “ability to provide large quantities of a safe and pure protein in a cost-effective manner will be particularly important in the light of current concerns over the safety of products derived from human plasma. It is in everyone's interest that we get these products to market as quickly as it is practical to do so.“ *

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