Scientists from the US and Japan have bred a dozen calves that don’t have prions – the infectious proteins that cause mad cow disease.

The research project is reported in the online journal Nature Biotechnology.

Preliminary tests suggest that the brains of the genetically engineered calves are immune to Bovine Spongiform Encephalopathy (BSE, or mad cow disease). The scientists verified this by trying to infect post mortem brain tissue from two of the 20-month old calves with prions, but the tissue remained healthy.

This follows a long process using donor cattle cells in which the gene known to trigger the production of prions was “switched off”. The cells were then used to create cloned calf embryos, of which 12 grew to term and were born free of prions. Three have been killed and used for brain tissue analysis, and the other nine have been injected with BSE to see whether they develop the disease or whether, as the scientists hope, they are immune since the gene responsible has been switched off. This could take several years since BSE can lie dormant for some time.

If the results are successful, the path to producing cattle free of BSE is not straightforward and could be years away. FDA approval must be sought before genetically engineered animals enter the human food chain. And, the current technology is not focused at food production but drug development.

This research is sponsored by a US biotech company, Hematech Inc, based at Sioux Falls in South Dakota. Representatives of the company suggest that BSE-immune cattle would be of great benefit to the production of human medicines like antibiotics, a field where thousands of cow embryos are used every year.

And the results of this research could also benefit the study of other diseases involving prions.

The risk to humans from animal BSE is currently very small in the US, following the scares that occurred in Europe, and the UK in particular, after which meat production and slaughtering regulations were tightened up. Also to reduce spread of the human version from human to human the FDA introduced strict regulations on blood donation by members of countries with a history of BSE.

In the last 20 years under 200 people worldwide have died from the human equivalent of BSE, thought to have come from eating infected animal products or from receiving transfusions from infected blood.

If BSE prions get into the human body they can trigger the human equivalent of mad cow disease – variant Creutzfeldt-Jakob Disease – vCJD. The prions cause havoc in the brain because they make the brain’s protein tissue form into unnatural patterns, gradually damaging the links between brain cells, the cumulative effect of which is a gradual wasting away of the brain. vCJD can take years to show symptoms and is invariably fatal. The only sure test on a live person is by sampling brain tissue, a very risky procedure.

Research into prions is still quite young, and scientists remain puzzled by exactly what controls their normal and abnormal behaviour and how the bad ones get “switched on” once they are in the body.

The remaining genetically engineered calves will no doubt be closely watched for any unexpected side-effects of being prion-free.

“Production of cattle lacking prion protein.”
Jürgen A Richt, Poothappillai Kasinathan, Amir N Hamir, Joaquin Castilla, Thillai Sathiyaseelan, Francisco Vargas, Janaki Sathiyaseelan, Hua Wu, Hiroaki Matsushita, Julie Koster, Shinichiro Kato, 5, Isao Ishida, Claudio Soto, James M Robl & Yoshimi Kuroiwa.
Nature Biotechnology Published online ahead of print: 31 December 2006

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Written by: Catharine Paddock
Writer: Medical News Today