UK moves ahead on the xenotransplantation issue

 
 
 
 

Rebecca Currie

Edinburgh

The guidelines are similar to those being adopted in the US and Spain (Nature Med., 4; 876, 1998) and call for post-transplant patient surveillance, preclusion of great apes as donor animals and strict control over the production and welfare of porcine donors. For now, UKXIRA, with the support of expert assessors, will advise ministers on individual applications for human trials, although to-date none have been made, and on developments in efficacy and safety research.

In keeping with this latter aim, a closed workshop was held in London a week after the new guidelines were issued, to discuss a key safety issue--the potential of pig endogenous retroviruses (PERVs) to transfer to human recipients of pig organs. The decision to hold a closed meeting contrasts with recent government efforts to broaden the debate on new medical technologies through open discussion ((Nature Med., 4; 875, 1998), and seems to be based partly on an odd presumption that the general public would not be interested in hearing the detailed scientific evidence.

Although UKXIRA will issue a report of its findings later in the year, those in attendance were unable to comment directly on the points raised. Nevertheless, coverage in the lay media of two of the studies presented, reporting no detection of PERVs in 35 patients who received either porcine islet cells or embryonic neurons (New Scientist, 159; 4, 1998), has stimulated a flurry of reports that pig organ transplants will be safe.

These positive reports are believed to have been tempered by evidence from academic groups at the UKXIRA meeting. Robin Weiss of the Institute of Cancer Research in London, whose group has studied three PERVs that selectively infect certain human cell types in culture (Nature Med., 3; 282, 1998) told Nature Medicine, "it is difficult to evaluate how infectious [PERVs] are for humans in the transplant setting." Weiss concedes that if the viruses were highly infectious, "we would be hearing the alarm bells by now from the handful of people who have been exposed that have been analyzed." But he added the caveat, "you could draw the conclusion that since blood is the only sample you can directly get a hold of, it might be the wrong place to look. It depends if you are an optimist or pessimist." In a written response to Weiss' concern, Imutran stated, "Other tissues are included in some of [our] studies and it is the general scientific consensus that blood is the best means of screening."

Speaking separately on the new guidelines, Weiss lamented that after early leadership by the British authorities in establishing appropriate regulatory measures, the UK has fallen behind the US Food and Drug Administration in gathering and evaluating scientific evidence.

He also believes that initial concerns about zoonosis—a particular British sensitivity after the BSE scandal—have not engendered a sense of urgency in scrutinizing the available scientific evidence. He sees the prevailing attitude as an embrace of the new technology, a view confirmed by UKXIRA panel member Janet Dewdney: "We would set ourselves firmly against a moratorium on xenotransplantation because we need to move forward...taking on board the science as it develops. The fact that there are a lot of unknowns would certainly not make me feel it was appropriate to have a moratorium."
 

"To date, we have found no evidence of cross-species transmission."