Xeno virus no problem: researcher

A new US finding, that transplanted human cells can form pig-human hybrid cells in foetal pigs, does not present a new hazard for transplants of humanised pig organs or cells into humans, according to a leading Melbourne xenotransplantation researcher.

Prof Ian McKenzie, of the Austin Research Institute in Melbourne, and CEO of XenoTrans, which is developing transgenic pigs for organ-transplantation experiments, said the discovery was not new, and only of "moderate interest".

Last week, researchers in the Transplantation Biology Program at the renowned Mayo Clinic in Rochester, Minnesota, reported that they had identified conditions under which pig and human cells could fuse in the body, yielding hybrid cells containing mixed genetic from both species.

The Mayo team, led by Dr Jeffrey Platt, also reported that the hybrid cells contained an HIV-like retrovirus, Porcine Endogenous Retrovirus (PERV) that could infect normal human cells.

Describing the finding as "completely unexpected", Platt said the observation helped explain how a retrovirus could jump from one species to another, and could lead to an explanation about the origin of diseases like AIDS and severe acute respiratory syndrome (SARS).

Platt said the discovery, which will be described in the March issue of the Journal of the Federation of American Societies for Experimental Biology (FASEB), could also help explain how cells in the general circulation became part of solid tissues.

But McKenzie said the discovery that somatic cells from different species could form fusion hybrids was "decades old", and was originally reported by an Australian researcher, Henry Harris, working at Oxford University.

Nor was the discovery that an endogenous retrovirus from one species could infect cells of another species -- more recently, researchers had shown that pig cells transplanted into SCID (severe combined immune deficient) mice produced PERV viruses that could infect mouse cells.

"Human cells also have receptors for PERV, but nothing done on the virus indicates infection leads to any disorder in pigs or any other mammals," McKenzie said. "There was a recent study in Germany in which researchers injected large doses of PERV into highly immunosuppressed piglets -- in the three months after the experiment, there was still no sign of RNA from the virus."

Asked if there was a risk that endogenous pig and human retroviruses could recombine in fusion-hybrid cells, giving rise to dangerous new retrovirus diseases, McKenzie said the risk had been investigated, and there was no evidence that such recombination occurred. Platt's team also found no evidence that PERV caused disease.

According to the Mayo Clinic researchers, scientists studying zoonoses -- human diseases of animal origin to another, like SARS -- want to know how viruses 'jump' from their host animal species to humans.

Zoonoses like influenza, which originated in birds, AIDS, which is believed to have originated in chimpanzees, and Ebola, whose animal host is still unknown, are among the world's devastating diseases. SARS is believed to have originated in a cousin of the mongoose, the Asian palm civet.