Rights: © Copyright. 2011. University of Waikato. All Rights Reserved. Published 9 November 2011 Download

Pig to human transplants, or xenotransplants, were banned in 1997 because of concerns about transmission of pig diseases to humans. This followed the discovery that pig endogenous retrovirus (PERV) from a pig cell line could infect human cells in a test tube. PERV is found in all pigs’ DNA as an inactive provirus, but it could potentially become active and release viral particles in other species. The pigs that LCT uses for transplant have PERV in very low amounts compared to other breeds. Since 1997, LCT and other research labs have shown that PERV does not infect human cells.

Questions to consider

  • What is unusual about PERV?
  • Why is it a concern for pig to human transplants?
  • Teaching points

    Learn more about diseases that might be transmitted from pigs to humans.
    Get information sheet: Pig viruses and pig testing

    Bob Elliott (Living Cell Technologies
    The history of our attempts to transplant these pig cells in capsules goes back to 1996 when we first did a couple of patients using a very primitive prototype. Unfortunately, we couldn’t continue on with that experiment because some news that pigs contained a virus, which might be transmitted to man, something akin to the AIDS virus, and that put a stop to everything.

    The particular virus called pig endogenous retrovirus, with a rather intriguing acronym of PERV, it’s not really a virus, it’s a provirus, it’s part of the DNA of the pig, and all pigs have it in varying doses, but in one particular instance, and where the whole scare came from, was in a lab in the United Kingdom, they found that some cultured pig cells from a particular strain of pigs, the provirus in the DNA could actually get out and start replicating outside the pig cell and could in fact infect a human cell that was in the same test tube with those pig cells. That was pretty bad news for us because it really meant that we just had to stop until we’d seen whether this occurred in all pigs – that is the release of the virus – and could the virus actually infect humans?

    Well, the first step we showed in our particular strain of pigs that the provirus remained where it should remain, locked into the DNA and not being reproduced as an active virus. The second step came from a number of studies done around the world, which we participated in, where it was shown that people who had received pig cells from all sorts of sources had not developed this particular virus infection. So it was apparent that, even though some of these pigs that had been used internationally probably did produce the virus, it still didn’t infect humans.

    Then the final piece of news came through, which I think was the most convincing, is that at one period, a blood factor from pigs was used for the treatment of people with a severe inherited bleeding disorder, haemophilia. A pig factor was given via the vein into people many times a month. It was subsequently found that the pig product, in fact, contained the retrovirus, the PERV virus. So many, many people had actually received injections into the vein of the very virus that we were all concerned about, and it did absolutely nothing, it did not infect humans. As it is, it’s turned out, this PERV virus is specific for pigs and not for humans. So that was a great relief to me, to say, well, even if our cells did produce the virus, it wouldn’t cause any harm.

    Michael Helyer
    Johnny Klemme