prion-free cows immune to BSE could be a reality soon

Main Category: CJD / vCJD / Mad Cow Disease
Article Date: 02 Jun 2004 - 21:00 PDT


A major advance towards producing prion-free cows that would be immune to mad cow disease has been made by researchers at companies in the US and Japan.

Their principal aim is to make genetically modified cattle that produce pharmaceuticals in their milk. But the companies hope that also making the animals resistant to BSE (bovine spongiform encephalopathy) will reassure consumers.

The researchers have now achieved the considerable feat of creating cell lines which have both copies of the cow's PrP gene switched off. The PrP protein can be switched to an infectious state by contact with a mutated prion. This switch causes prion diseases such as BSE in cows and variant Creutzfeldt Jakob Disease (vCJD) in humans.

Making live animals from these cell lines should be relatively straightforward using cloning techniques similar to those that created Dolly the sheep.

The companies say they have no intention of producing prion-free animals destined for human consumption. Instead they want to assuage public fears about pharmaceuticals derived from cow's milk, even though the process used to extract proteins from milk has already been shown to remove prion contamination.

Consumer choice

"Because of public perception, we feel an added benefit would be to knock out the gene and remove the possibility that the animals could be infected," says James Robl, chief scientific officer at US biotech company, which carried out the research jointly with the Kirin Brewery in Tokyo, Japan. "Japanese consumers have a high degree of concern about BSE."

Some experts have suggested creating prion-free cattle to eliminate BSE from the beef herd. But it is not clear that consumers would prefer genetically modified beef over meat that has a very small chance of infection with prions. To date there have only been around 140 cases of vCJD in total worldwide, although the ultimate extent of the human epidemic remains uncertain.

Furthermore, replacing beef herds with prion-free cattle would take decades. "Getting a herd of any size would be quite difficult," says Harry Griffin at the Roslin Institute in Scotland, where Dolly was cloned.

Another question mark hangs over what effect knocking out both copies of PrP will have on cows. Mice lacking both copies appear to be normal, although some disputed research suggests they may have disrupted sleep patterns.

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