Cattle immune to mad cow?

WASHINGTON — Scientists said this week they have used genetic-engineering techniques to produce the first cattle that may be biologically incapable of getting mad-cow disease.

The animals, which lack a gene that is crucial to the disease's progression, were not designed for use as food. They were created so that human pharmaceuticals can be made in their blood without the danger that those products might get contaminated with the infectious agent that causes mad-cow disease.

That agent, a protein known as a prion (pronounced PREE-on), can cause a fatal human ailment, variant Creutzfeldt-Jakob disease, if it gets into the body.

More generally, scientists said, the animals will facilitate studies of prions, which are among the strangest of all known infectious agents because they do not contain any genetic material. Prions also cause scrapie in sheep and fatal wasting diseases in elk and minks.

The research was published in the online journal Nature Biotechnology.

"This research is a huge step forward for the use of animal biotechnology that benefits consumers," said Barbara Glenn of the Biotechnology Industry Organization. Among the industry group's members is Hematech, the Sioux Falls, S.D.-based company that created the gene-altered cattle.

Prions, which are normal protein components of the brain, immune system and other tissues, cause disease only when they "go bad." For these long strands of protein, that means folding themselves into three-dimensional shapes that are slightly different from their conventional conformation.

First, the Hematech scientists cultivated a colony of cattle cells in a laboratory dish. Then they used a genetic-engineering method to "knock out" just one gene inside each cell — the gene that directs the production of prion proteins.

Finally, using cloning techniques, the team grew a dozen calves, each from one of those altered cells. Today, as far as scientists can tell, those 12 cattle are wholly lacking in prions.

The cattle are now being injected directly with mad-cow disease to make certain they are immune to it.

Material from The Associated Press is included in this report.