Prockop's team injected the adult bone marrow stem cells, which have the ability to mature into several types of cells, into the mice's hearts. Using a genetic marker, he found that the cells had traveled to the pancreas in about two weeks.

At that point, the mice's blood sugar levels began to fall to about half that reached before treatment. In addition, the mice were making increased levels of mouse insulin, rather than human insulin.

That suggested that the human cells were contributing to the repair of the mouse pancreas, Prockop said. His studies have shown that stem cells can "loan" energy-producing structures called mitochondria to other, sick cells.

"These cells are remarkable," he said. "They're part of a natural repair system we all have, and all we're trying to do with our strategy is increase their levels."

Researchers noted in a series of studies published Sept. 21 in the New England Journal of Medicine that adult bone-marrow stem cells can increase pumping power in damaged human hearts. Those studies have also shown that the stem cells themselves don't begin growing heart muscle, and researchers have theorized that they somehow contribute to tissue repair.

Kidney repairs

Prockop noted that the stem cells also traveled to the mouse's kidney. The kidney also showed signs of repair, with lower levels of immune cells called macrophages that repair infections, and a healthy thickening of tissue between kidney cells.

Companies including StemCells Inc. and Aastrom Biosciences Inc. are developing treatments for a variety of diseases using adult stem cells. Prockop said he is applying for Food and Drug Administration permission to test take human bone marrow cells, grow them in a dish, and inject them into people with diabetes.

"We think the dangers are minimal," he said. "We may be able to repair the eyes, heart, brain and peripheral circulation."