BBC Health Correspondent Richard Hannaford: "Some say the research is flawed"

The study carried out in Cambridge found that people who receive transplanted pig organs are unlikely to contract incurable, infectious diseases.

There has been a widespread fear that if such operations were approved, pig viruses might spread to humans in a similar way that HIV seems to have done from chimps.

The study of 160 patients, who have been treated with various living pig tissues over the past 12 years, appear to show these fears are groundless.

The severe shortage of human transplant donors makes the use of organs from other species (xenotransplantation) an appealing alternative to many patients and doctors.

Imutran's Dr David White: These findings are good news for the future of transplantation

Pigs look to be the most promising source of these organs because the animals are close in size to humans and are easy to breed in large numbers.

Scientists have already made great progress in altering the genetic make-up of pigs so their tissues are less likely to be rejected by the human immune system.

The new data, published in the journal Science, will now intensify the pressure on regulatory authorities in a number of countries to allow full-organ transplant trials to proceed.

In Britain, the UK Xenotransplantation Interim Regulatory Authority (UKXIRA) will screen applications, with government ministers giving the final approval.

Health Secretary Frank Dobson has already said that safety is the key issue, having accepted that there should be no ethical objection to this kind of operation.

Dormant viruses

One of the frontrunners in this field is the UK biotechnology company Imutran Ltd, based in Cambridge. It was also responsible for leading this latest study on the dangers of pig viruses.

Of particular concern is the porcine endogenous retrovirus (Perv), which has become a permanent part of pigs' DNA and is passed on to new generations in eggs and sperm.

The authors looked at individuals who have already received pig tissue for a number of conditions for any signs that Perv had infected their cells. These patients included people who have received skin grafts, and diabetics who have been given insulin-making cells taken from the pancreas of pigs.


The study found no evidence of Perv infection, even in 36 patients who had their immune systems suppressed with drugs as part of their treatment and were therefore presumed to be at increased risk of infection.

The BBC's Richard Hannaford reports on the experiments with pig tissue

Samples from some of the patients did contain some Perv DNA, but this appears to be due to the fact that these patients were still carrying pig cells in their bloodstream, a phenomenon known as "microchimerism".

The authors were surprised to learn that pig cells can last for so long in the patient - even 8.5 years after a transplant - but argue this merely shows that pig tissue can survive in the human body for long periods with no ill effects.

'Some reassurance'

"We have learned a great deal from this study," said the lead author Dr Kaz Paradis, Director of Clinical Research at Imutran. "But it is important to remember that any move to clinical trials will only take place following open discussion with scientific and clinical experts, and with full approval from the appropriate regulatory authorities."

Professor Sir Roy Calne, a transplant pioneer who developed the anti-rejection drug cyclosporine A said: "This study adds considerably to the breadth and depth of the knowledge that the scientific community continues to accumulate as we explore the potential for xenotransplantation in the clinical setting."

There is a chronic shortage of donor organs

However, Robin Weiss of the Institute of Cancer Research in London, issued a strong note of caution. It was his research that helped to provoke much of the recent concern after he demonstrated that two pig viruses could transfer to human cells under certain laboratory conditions.

Having reviewed the new data, he said the study "offered some reassurance" on safety. But he said "the ethical and technical problems of maintaining vigilance over xenotransplantation should not be underestimated."

Compassion in World Farming condemned the latest research. The animal welfare group said xenotransplantation was unethical and the study provided no reassurance as far as it was concerned.