Technologies
Cattle genetically engineered to avoid mad cow disease
By Ben Wasserman - foodconsumer.org
Dec 31, 2006 - 4:51:58 PM

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Those who eat beef do not have to be at higher risk of contracting mad cow disease.  Researchers have genetically engineered healthy cattle that may resist mad cow disease although further testing continues, according to new research published in the journal Nature Biotechnology.

Mad cow disease or bovine spongiform encephalopathy (BSE) in cattle is believed to be caused "by propagation of misfolded forms of the normal cellular prion protein PrPC, such as PrPBSE in bovine spongiform encephalopathy (BSE) in cattle and PrPCJD in Creutzfeldt-Jakob disease (CJD) in humans," according to the researchers.

People may contract variant CJD or vCJD, a deadly brain wasting disease in humans, by eating beef from cattle with mad cow disease.   In the UK, hundreds of people have already died from the disease and thousands of people might have contracted the disease without knowing it, according to early news reports.

These cows, on a farm in South Dakota, were genetically engineered by scientists to be prion-free, which likely makes them resistant to mad cow disease. (courtesy of Hematech, Inc)

Using a gene targeting system that was originally developed to produce drugs such as antibodies in cattle, researchers from Hematech, Inc (a subsidiary of the Kirin Brewery Company, Ltd), a pharmaceutical research company based in Sioux Falls, S.D., knocked out the gene that is responsible for production of prion protein known as PrPC in the studied cattle, making the cattle prion-free.

"By knocking out the prion protein gene and producing healthy calves, our team has successfully demonstrated that normal cellular prion protein is not necessary for the normal development and survival of cattle. The cows are now nearly two years old and are completely healthy," stated James M. Robl, Ph.D., President and Chief Scientific Officer of Hematech.

"Hematech has already successfully produced knockout cattle using the sequential gene targeting system. We anticipate that prion protein-free cows will be useful models to study prion disease processes in both animals and humans."

In the current research, researchers from the Agriculture Research Service or ARS-USDA's chief intramural scientific research agency with assistance from researchers at Hematech and the University of Texas meant to evaluate the prion-free cattle to see if there are any developmental abnormalities in the GM cattle and if the cattle resist prion diseases.

"The cattle were monitored for growth and general health status from birth up to 19 months of age. Mean birth and daily gain were both within the normal range for Holsteins. General physical examinations, done at monthly intervals by licensed veterinarians, revealed no unusual health problems," said Juergen Richt, lead author of the report, from ARS' National Animal Disease Center (NADC) in Ames, Iowa.

"At over 20 months of age, the cattle are clinically, physiologically, histopathologically, immunologically and reproductively normal. Brain tissue homogenates are resistant to prion propagation in vitro as assessed by protein misfolding cyclic amplification," the authors write in their report.

The researchers said, "the PrPC-deficient cattle may be a useful model for prion research and could provide industrial bovine products free of prion proteins."

"These cattle can help in the exploration and improved understanding of how prions function and cause disease, especially with relation to bovine spongiform encephalopathy, or BSE," said Edward B. Knipling, administrator of ARS.

The prion theory is just one of a few theories to explain the mad cow disease, according to a scientist affiliated with foodconsumer.org.  Not all types of vCJD or brain wasting diseases seem to be equally fetal.   Evidence has indicated that there may be various forms of brain wasting diseases in humans.

Further testing on the GM cattle will be completed in three years, according to the ARS.  It remains to be seen if the prion-free animals resist mad cow disease.

(Kuroiwa, Y et al. Production of cattle lacking prion protein. Nature Biotechnology Published Online December 31, 2006; DOI: 10.1038/nbt1271).