- 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.
Dr David White: These findings are good news for the future of transplantationPigs
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
- 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
- </olmedia/425000/audio/_425436_hannaford.ramThe BBC's
Richard Hannaford reports on the experiments with pig tissueSamples 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 organsHowever, 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
- 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.
- "The transplant of pig tissue cannot be compared
to transplanting a whole organ, which may be a larger reservoir of viruses,"
a spokeswoman said. "Also, negative results cannot be a complete proof:
They may indicate an absence of viruses, but they may also merely reflect
a failure to detect them."