london

An international panel of scientists is due to meet in London today (6 August) to discuss the results of organ-transplant studies. These are likely to send mixed signals on whether it is safe to transplant animal organs into humans.

The meeting is a closed one-day workshop organized by the UK Xenotransplantation Interim Regulatory Authority (UKXIRA). The topics for discussion are expected to include “promising results” from an industry-funded study of 150 patients already treated with living pig tissue, such as islet cells for the treatment of diabetes.

But academic researchers from Britain are expected to announce the results of a study showing that a variant of a pig retrovirus previously thought to be safe can infect human cells under laboratory conditions.

The meeting comes a week after the British government released its guidelines on regulating xenotransplants. These say that the Secretary of State for Health will decide on each application for a human trial of an organ transplant, based on advice from UKXIRA. The authority, in turn, will be supported by a number of expert assessors.

The welfare of animals bred for human transplants will be included in UKXIRA's terms of reference. And the government's advisory committee on dangerous pathogens is to set up a working group to investigate the risks of infection from different forms of xenotransplant therapy. The guidelines endorse a Home Office ban on the use of primates as organ donors.

The move has been welcomed by companies developing animal organs for human transplants, as it allows them to apply to proceed with human trials. A statement from Imutran, the xenotransplant arm of the life sciences company Novartis, described the announcement as “an important step”.

Today's meeting was arranged to discuss the latest research on whether pig viruses can transfer into humans. This is one of the main concerns holding up regulatory approval for animal-to-human transplants.

Researchers have been able to eliminate most non-inherited viruses from human transplant organs bred in pigs. But there are four known variants of a pig virus — the porcine endogenous retrovirus (PoERV) — found in the chromosomes of pigs that cannot be eliminated.

Two of the four variants of PoERV are known to be capable of crossing the species barrier and infecting human cells. But today's meeting is expected to hear of a third virus, not found in all pigs, that has been found to infect a human cell line under laboratory conditions.

Better news for proponents of xenotransplants is expected from a study organized by Imutran of 150 patients who have been treated with living pig tissue. Samples were collected from patients worldwide. Each was analysed twice — by a laboratory in the United Kingdom and by one in the United States — to see if the pig retrovirus had transferred to any patient.

“The results are very interesting,” says David Onions, an adviser to Imutran and director of the Glasgow-based laboratory Q1 Biotech, which analysed one set of samples. Onions says he cannot provide further details until the data are published. But he describes them as “encouraging”.

Imutran is relying heavily on the results of this study for its plans to develop xenotransplant organs. The next step, according to a company statement, is to attach transgenic livers outside the body of a small number of patients waiting for a liver transplant, enabling the pig livers to work along the lines of a liver dialysis machine.

The pig liver would work for about 48 hours, allowing doctors extra time to find a suitable human liver for transplantation. “This study will then be reviewed to assess the safety and efficacy of the transgenic organs,” says the statement.

Imutran is not the first to use such a technique. An analysis by the Institute of Cancer Research in London, of two cases of pig kidneys similarly attached to patients, has been accepted for publication in a medical journal.

Meanwhile, the US Food and Drug Administration is due to publish guidelines on xenotransplantation this autumn. These are expected to advocate long-term monitoring of recipients and a possible ban on the use of non-human primates (see Nature Medicine 4, 876; 1998).