An eminent transplant surgeon has poured cold water on suggestions that animal organs could be used in humans in the near future.

Sir Roy Calne, professor of surgery at Cambridge University, said that there were "formidable" scientific barriers to such transplants, known as xenotransplantation. It would be hard to judge when the science was sufficiently developed for human trials to be ethical, he said.

Professor Calne's comments coincided with the launch of a report on xenotransplantation by a working party of the Nuffield Council on Bioethics. The report endorses transplantations from pigs subject to strict controls from an advisory committee.

Professor Calne said: "The main worry is that there is still a long way to go in the science of getting a xenograft to be accepted. Every protein made by man is different from that made by a pig." So far, he said, one pig protein has been successfully transferred - a protein that inhibits the action of complement, a key in the body's immune process. "That is one human protein out of millions," he said.

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David Morton, professor of biomedical science and biomedical ethics at Birmingham University and a member of the working party, said that veterinary researchers would become increasingly involved in medicine as animal/man comparisons became important.

Professor Morton said: "We'll need vet microbiologists with knowledge of pig diseases and of the organs that pigs carry. We need a great pooling of information."

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Nobody knows, for example, whether a kidney transplanted from a pig, once in the human body, would cause chemicals to be secreted into the bloodstream in quantities appropriate to a pig or to a human.

Another question surrounds the fact that some diseases are transmitted by inhalation, said Professor Morton. Will a farmer implanted with a pig's lung come down with some disease specific to pigs if he breathes in a pig virus while he is working?

The working party was chaired by Albert Weale, professor of government at the University of Essex.

Xenotransplantation hit the headlines last year when a Cambridge company, Imutran, announced that it had overcome the major barriers to transplanting pig organs.

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