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Mixing of Human, Mouse Cells Poses Problems To Researchers

By Justin Gillis and Ceci Connolly
THE WASHINGTON POST

WASHINGTON

Most or all of the human embryonic stem cell colonies approved for research funding under a new Bush administration policy have been mixed in the laboratory with mouse cells, which may create substantial hurdles for scientists trying to turn the colonies into treatments for Parkinson’s disease, spinal-cord injuries and other ailments.

The cell colonies, or “lines,” were originally created for early stage research with no thought that they would become the only embryonic cells eligible for federal money. But that’s the status President Bush conferred on them in his first prime-time address to the nation on Aug. 9.

The standard technique for creating human embryonic stem cell lines has been to extract cells from inside a microscopic embryo, then grow them atop embryonic mouse cells, known as “feeder” cells. The latter excrete some unknown nutritional or growth factor that helps the human cells stay healthy. Because they’ve been in close contact with mouse cells, the human cells pose a small but real risk of transferring potentially deadly animal viruses into people.

Because of that, under guidelines the Food and Drug Administration has been developing for several years, it would be difficult, though not impossible, to use the cells in human clinical tests.

Under the FDA rules, which are designed to prevent the accidental creation of a new plague, transplants of these embryonic cells into people would be treated as though they were “xenotransplants,” or transplants of animal tissue. The guidelines impose stringent requirements on researchers and patients alike. They would probably rule out some groups of patients who might otherwise be eligible to participate in human stem-cell tests -- notably, for instance, young diabetes patients whose disease can be treated in other ways.

The human embryonic stem cell lines reported in scientific literature were all grown in direct contact with mouse cells and might have picked up mouse viruses, which government officials acknowledged will bring them under the FDA policy.

Scientists are working on ways to grow human embryonic cell lines without using mouse cells, but any new ones created after Bush’s Aug. 9 speech would be ineligible for federal research money.

Patient groups and people who work with them expressed concern when told about the xenotransplant restrictions.

“This would be the exclamation point” on an already lengthy list of questions about the quantity and quality of the cell lines eligible for research funding under the Bush policy, said Kevin Ryder, a consultant to the American Cell Therapy Research Foundation, a New York foundation that supports research into many types of treatments using cells.