Two new studies have shown that insulin-producing islet cells from the pancreases of newborn pigs can reverse type 1 diabetes in primates. The findings, from teams in Canada and the US, pave the way for human clinical trials.

If the trials are successful, millions of people with type 1 and type 2 diabetes could eventually benefit from treatment with piglet cells.

Transplants of insulin-producing islet cells have long been considered a promising therapy and the first experiments using human cells were conducted as far back as 1977.

Though the procedure has had encouraging results, prospects have been limited by an acute shortage of human tissue for transplants, which typically require islets from two pancreases donated after death. Only about 800 donor pancreases are available for transplant in Britain each year. Scientists have turned to pigs as a potential source of islet cells because the animals produce a similar form of insulin to humans.

Grafts of tissue from animals, however, pose ethical and safety concerns because they raise the prospect of introducing viruses and other pathogens that might prove harmful.

Pigs carry viruses known as porcine endogenous retroviruses, which have written themselves into the animals’ genetic code. While these cause the pigs no harm, there are concerns that they could trigger diseases in humans.

There is currently a moratorium on xenotransplantation in Britain, though human experiments using pig islet cells have been conducted in Mexico.

The new studies, one by the University of Minnesota and the other by the University of Alberta, each examined the potential of islet cells from newborn piglets transplanted into diabetic rhesus macaque monkeys. Both are published in the journal Nature Medicine.

In the Alberta study, the transplants worked so well that the four monkeys involved have been able to come off insulin injections, one for almost a year. The Minnesota team achieved similar results.

The transplants offer an encouraging indication that the procedure is probably safe. Ray Rajotte, Professor of Surgery at the University of Alberta, said: “The next step is to prove that these neonatal porcine islet cells could become a source for human transplantation.

Should the technique work in people, it would require them to take immunosuppressant drugs to minimise the possibility that the pig cells would be rejected. These have side effects, making transplants a less attractive option for patients whose diabetes is well controlled with insulin injections.

In the longer term, human embryonic or adult stem cells might be used to grow islet cells for transplant, which could be cloned as a perfect genetic fit for patients or matched from large stem cell banks. Jo Brodie, islet project co-ordinator at Diabetes UK, said: “A major limiting factor in the use of either whole pancreas or islet cell transplantation is the lack of available donor organs.

“This research offers the potential for a new source of islet cells.”

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