Still, Weir cautioned that more studies are needed to make sure the treatment works and is safe. "It's really too early to suggest to people that this is a cure," he said.

The patients involved were ages 14 to 31 and newly diagnosed with Type 1 diabetes. An estimated 12 million to 24 million people worldwide — including 1 to 2 million in the United States — have this form of diabetes, which is typically diagnosed in children or young adults. An autoimmune disease, it occurs when the body attacks insulin-producing cells in the pancreas.

Insulin is needed to regulate blood sugar levels, which when too high, can lead to heart disease, blindness, nerve problems and kidney damage.

Burt said the stem cell transplant is designed to stop the body's immune attack on the pancreas.

A study published last year described a different kind of experimental transplant, using pancreas cells from donated cadavers, that enabled a few diabetics to give up insulin shots. But that requires lifelong use of anti-rejection medicine, which isn't needed by the Brazil patients since the stem cells were their own.

The 15 diabetics were treated at a bone marrow center at the University of Sao Paulo.

All were newly diagnosed, before their insulin-producing cells had been destroyed.

That timing is key, Burt said. "If you wait too long," he said, "you've exceeded the body's ability to repair itself."

The procedure involves stimulating the body to produce new stem cells and harvesting them from the patient's blood. Next comes several days of high-dose chemotherapy, which virtually shuts down the patient's immune system and stops destruction of the few remaining insulin-producing cells in the body. This requires hospitalization and potent drugs to fend off infection.

The harvested stem cells, when injected back into the body, build a new healthier immune system that does not attack the insulin-producing cells.

Patients were hospitalized for about three weeks. Many had side effects including nausea, vomiting and hair loss. One developed pneumonia, the only severe complication.

Doctors changed the drug regimen after the treatment failed in the first patient, who ended up needing more insulin than before the study. Another patient also relapsed.

The remaining 13 "live a normal life without taking insulin," said study co-author Dr. Julio Voltarelli of the University of Sao Paulo. "They all went back to their lives."

The patients enrolled in the study at different times so the length of time they've been insulin-free also differs.

Burt has had some success using the same procedure in 170 patients with other autoimmune diseases, including lupus and multiple sclerosis; one patient with an autoimmune form of blindness can now see, Burt said.

"The body has tremendous potential to repair," he said.

The study was partly funded by the Brazilian Ministry of Health, Genzyme Corp. and a maker of blood sugar monitoring products.

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Contributing: Carla K. Johnson.