By CAROL M. OSTROM
The Seattle Times

In a bold experiment, Seattle researchers are seeking to cure severe Crohn's disease by giving patients a new immune system.

The clinical trial, which just received final approval, will look at a side effect of bone-marrow transplantation that researchers at the Fred Hutchinson Cancer Research Center noticed years ago: A handful of leukemia patients given donor marrow cells were also cured of their Crohn's disease, a chronic intestinal inflammation.

Essentially, the idea behind the new study is simple: "It's swapping out an old, diseased immune system for a new immune system, which we hope -- and our research would support -- will take care of the Crohn's disease," said Dr. George McDonald, the study's principal investigator.

McDonald said until recently, it was unthinkable to offer a bone-marrow transplant for a non-life-threatening disease.

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