Tissue recipients are free of pig virus.

A new study bodes well for organ transplants and other medical treatments that mix human and pig cells. Researchers examined 160 patients who had undergone, during the past 12 years, a variety of experimental procedures that use pig tissue. In some cases, physicians had run patients' blood through external pig spleens, livers, and kidneys. Other treatments included grafts of pig skin and transplants of porcine pancreatic endocrine cells.

Although potential benefits of transplanting a pig's heart, kidney, or other tissue to humans are great, such experimental procedures may also be dangerous. The patient's immune system may reject the porcine tissue, or the pig's organ may not function smoothly in its new host. Physicians have also recognized a third obstacle. Pig tissue might infect patients with viruses that don't otherwise infect humans.

One such microbe is porcine endogenous retrovirus, or PERV, which all pigs carry without showing any symptoms (SN: 4/19/97, p. 245).

A report in the Aug. 20 SCIENCE, however, indicates that pig-tissue treatments don't infect humans with PERV. Using a technique known as polymerase chain reaction to search for the retroviral DNA in patients' blood, researchers led by Khazal Paradis of Imutran, a biotechnology company in Cambridge, England, found that none of the patients treated with pig tissue was infected with PERV. Although 23 patients retained some pig cells for up to 8 1/2 years after treatment, they showed no sign of the virus.

In an editorial accompanying the report, Robin A. Weiss of University College London remarks, "For the individual transplant recipient, the real promise seems to be greater than uncertain peril." Indeed, pig-to-person transplantation might pose a lesser threat of infection than a graft from an unknown human donor does, he says.