Medical scientists have made a breakthrough in attempts at transplanting pigtissue into humans suffering from diabetes.

Medical scientists have made a breakthrough in attempts at transplanting pigtissue into humans suffering from diabetes.

The researchers believe they have overcome one of the biggest barriers that leads to insulin-making cells from pigs being rejected when transplanted into another species.

A team from Hammersmith Hospital in London has developed a way of substantially delaying the rejection of pig pancreatic cells when transplanted into laboratory mice.

In a study published in the journal Nature Immunology, the scientists have shown that transplanted pig tissue can survive in the mice for six weeks, which is three times longer than it normally takes to be rejected.

Professor Robert Lechler, head of immunology at Imperial College of Science, Technology and Medicine and leader of the Hammersmith study, said that further improvements should be possible and that transplants of pig pancreatic cells into humans could take place in three to five years.

"Our findings offer a novel solution in the battle to get foreign organs accepted by human bodies. Eventually, we hope that using foreign organs in humans may start to solve the huge shortage of organ donors across the world," Professor Lechler said.

The breakthrough exploits the complicated mechanism the body employs to recognise and reject alien material, whether it is potentially harmful bacteria or tissue transplants from another species.

One way of rejecting foreign tissue is for the body's white blood cells, the T-cells, to be stimulated into identifying and attacking the alien cells. Certain proteins - called CD86 - on a pig's pancreatic cells cause this stimulation.

The Hammersmith scientists have found a way of interfering with this stimulation process by "immunising" the mice against the protein on the pig tissue which would otherwise have encouraged the mice's immune system to identify and attack the alien tissue.

Professor Lechler said that although the pig pancreatic cells were eventually rejected by the mice after six weeks, it should be possible to refine the technique still further to prevent rejection altogether. Transplanting human pancreatic cells into diabetic patients has already been done with limited success using the most modern anti-rejection drugs.

However, being able to use pig pancreatic transplants could solve the acute shortage of donated organs and tissues, said Lord Winston, director of research and development at Hammersmith Hospital.

"Several thousand people a year die awaiting organ transplants in this country. This remarkable work is a major advance in obtaining donor organs which could save many lives every year," he said.

Separate work on animal transplants by Imutran, a biotechnology company based in Cambridge, has focused on overcoming the "hyperacute" rejection of organs that occurs within minutes of a transplant.