"I am here to represent the voices of dying patients," said Mr Jeffrey Getty, an HIV-positive activist on AIDS who supports the use of animal tissues in human transplant patients. He is also the recipient of a baboon bone-marrow transplant, used in a life-saving operation two years ago.
Mr Getty believes irrational fears are "tainting the debate" about the use of animal tissues in transplants. "What we are crossing here is a deep-seated psychological fear," he told delegates to the American Association meeting in Philadelphia. The US government was considering legislation to curtail or block continued experimentation in this field, known as xenotransplantation.
"I am urging that the science advance and move forward," he said, to allow research to go ahead, but with further research and trials before the widespread application of xenotransplantation.
The use of animal tissues was described as "an incredibly powerful tool to fight disease" by Dr Jeffrey Platt, of Duke University. "There is no way to supply the tissues and organs needed by patients," he said. Supply fell far short of demand for these transplant tissues.
Xenotransplantation had a number of advantages, he said. It could overcome existing shortages and also allowed for forward planning. This contrasted with the current situation where patients must await another's death before lifesaving organs became available. Work was under way to find ways of genetically altering the donor tissues so they would not be rejected by the recipient's immune system.
Opponents claimed there was a risk of animal viruses mutating in human hosts, thus representing a risk to the general population. "The issue isn't whether viruses from animals will jump to humans because they will," Dr Platt said. Influenza viruses usually began as animal or avian viruses. But this spontaneous transfer would not occur in xenotransplantation.
Nor was this form of transplantation a rare event. While the baboon marrow transplant was the first of its kind, there had been hundreds of thousands of pig-skin grafts on burn victims. There had also been some use of animal blood products.
"Right now, an estimated 300,000 patients will die in the US because we can't get a donor match," said Dr Suzanne Ildstad, of Allegheny University of the Health Sciences. Half of all patients awaiting a heart transplant would die before a donor could be found.
"That is the motivating force behind this research. We either have to make the decision that not everyone will get a transplant or find alternative sources." Experimentation in this field enhanced research in nonxenotransplantation technology, she added.
The next step in human-to-human marrow transplantation was the genetic manipulation of the marrow before injection into the recipient. This had the potential to reduce or prevent graft versus host disease, when the donated marrow attempts to reject the recipient's tissues.