Two Canadian patients have undergone an experimental transplant of pig cells to treat their Type 1 diabetes. But international authorities have asked their Mexican doctor to stop performing the procedure, saying there isn't enough evidence that it's safe for humans.

CTV first covered the controversial work of Dr. Rafael Valdes in 2004 for the investigative series W-FIVE.

Dr. Valdes takes insulin-producing cells from six-day-old piglets, and puts them into a small chamber previously implanted in a human patient's abdomen.

The pig cells then appear to produce insulin, a vital hormone which the patient's own body can no longer make.

The process known as xenotransplantation -- animal-to-human transplantation -- and it is one of the most promising areas of research for diabetes.

There is no cure for type 1 diabetes, and it is mainly treated with insulin injections.

Dr. Valdes, a prominent transplant surgeon, published results of transplanting porcine insulin last year in the European Journal of Endocrinology.

The peer-reviewed study involved 12 teenaged Mexican patients, and concluded the procedure is safe and effective.

Half the teens in the study who received the pig cells -- some as far back as six years ago -- needed less insulin. Two patients were able to drop the insulin shots altogether.

And Dr. Valdes says the procedure seems to slow damage to their kidneys, nerves and eyes.

Such organ damage and chronic disease is common among diabetes patients. The disease is responsible for most cases of blindness in Canada, and is the second-leading cause of kidney failure.

However, some of Dr. Valdes' colleagues have been unable to find evidence of porcine insulin in the lab samples he's provided to them, and they've been unable to replicate his results in animals.

Dr. Valdes has been following up on the work of a team of University of Alberta scientists, who were able to transplant human pancreatic islet cells into patients in 1999. Their method was dubbed "The Edmonton Protocol."

However, due to a shortage of human donors for these cells, other researchers around the world have been experimenting with the idea of transplanting pig islet cells.

Dr. Valdes credits his success to the small metal cylinder, the size of a cigarette, which he called the "Valdes chamber." His technique helps prevent rejection of the donor cells.

Patients sing praises

Two Canadians have undergone the procedure so far.

"I decided I didn't have anything to lose," says Toronto schoolteacher Teresa Hibbert, who had the procedure done one year ago.

At age 53, she is the only adult to have taken the Valdes treatment. It isn't a total cure, but she's noticed benefits.

"I can eat certain foods better than I did before, and my sugar levels don't go as high as they did before," Hibbert says.

Hibbert wants to return to Mexico for further treatment, but will have to wait.

Despite reports of progress, the International Xenotransplantation Association, which monitors animal to human transplants, has demanded Dr. Valdes stop implanting pig cells into any more patients.

Dr. Valdes has the support of some scientists, including Dr. David White, a professor of Xenotransplantation at the University of Western Ontario. "Clinically, his work has extraordinary potential," Dr. White told The Globe and Mail. "Our objective is to have this technology introduced in Canada."

The National Committee for Bioethics will review the ethics and results of Dr. Valdes' study. Meanwhile, he is conducting more studies in rabbits and humans and hopes to resume human trials at the end of the year.

With a report by Avis Favaro, CTV News medical specialist