Mice that got experimental transplants of pig cells became infected with a pig virus, providing new evidence about the possible risks of transplanting animal tissue into people, researchers report.
The mice remained healthy and the virus apparently replicated only a couple of times before going dormant, a preliminary but hopeful indication, said study author Dr. Daniel R. Salomon of the Scripps Research Institute in La Jolla, Calif.
''At the moment ... the risk here is unclear. It doesn't appear to be very great,'' Salomon said. With further research, ''there's every possibility ... that we will demonstrate this virus is nothing to be concerned about.''
He did the federally funded study with colleagues at Scripps and elsewhere. It was released Wednesday by the journal Nature, which said a date for its publication has not yet been set.
Scientists are interested in pig-to-human transplants as a way to relieve the shortage of human organs and tissue.
But that promise has long been shadowed by concerns over ''endogenous'' viruses in pigs. Eons ago, these viruses infected the ancestors of modern pigs. The viruses' DNA mingled with the animals' own genes and is now simply inherited along with pig genes.
The concern has been that if pig tissues are transplanted to people, this viral DNA might make viruses that will infect people. That might unleash an infectious disease previously unknown in people.
The new study involved transplanting pig islet cells to mice, because such transplants are being discussed for treating diabetes. The researchers later found DNA evidence that some mouse tissue had been infected with endogenous pig virus.
Dr. Jay Fishman of Harvard Medical School, who did not participate in the study, called the work important. But he cautioned it would take further experiments to prove the mouse tissue truly became infected.