Pig-to-human tissue transplants 'imminent'

Trials could begin in the US within two years – but British expert warns that safety fears remain

The world is on the cusp of a medical revolution which will see transplants of tissue from genetically engineered pigs to treat a range of human diseases, US scientists say today.

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Human trials could begin within two to three years of tissue taken from specially bred pigs to help the millions of sufferers from diabetes, brain diseases and blindness.

But a British expert challenged their findings saying the safety issues were still "unresolved". The fear is that a retrovirus could jump from pigs to humans and trigger a new pandemic – HIV is thought to have started from a cross-species infection.

In a review of xenotransplantation – using animal tissue and organs to replace human ones – experts from the Thomas Starzl Transplantation Institute at the University of Pittsburgh say the technology has made "great strides".

During the mid-1990s, Imutran, a small biotechnology company in Cambridge, became the first in the world to transplant pigs' hearts into monkeys, demonstrating that cross-species transplantation was possible. However, immune system rejection problems proved more difficult than expected and safety fears dampened enthusiasm.

A decade on, attention has focused on the transplant of cells and tissues rather than organs – pancreatic islets for diabetics, brain cells for Parkinson's disease and corneas for the blind.

Problems remain, including loss of transplanted cells, blood clots and other rejection problems. New, genetically modified pigs will shortly become available which could overcome these issues and make human trials of transplanted tissue "imminent".

The US scientists discount safety fears saying retroviruses "do not pose a substantial risk".

That was challenged by Robin Weiss, professor of virology at University College, London, and an expert on retroviruses. He said yesterday: "I don't think the risk issues have been resolved. That doesn't mean clinical trials shouldn't go ahead but there would need to be very close monitoring of patients to ensure they were not picking something up from pigs."