While pig livers are being tested for their ability to buy time for patients awaiting liver transplants (see related story), other research has suggested that the path to xenotransplantation may have a few stumbling blocks.
Researchers at London's Institute for Cancer Research have suggested in two separate reports that pig organs contain viruses that may be transmissible to humans.
In March, Robin A. Weiss and colleagues reported in Nature Medicine (1997;3:282-286) that retrovirses from pig cells could infect human kidney cells in vitro. They wrote that latent infections could exist that "are asymptomatic in their natural host, but which could cause disease in the xenografted recipient." The possibility of transmission from donor tissue to a human host "is more plausible than a fanciful scare story," they said.
In the October 16 issue of Nature (1997;389:681), Dr. Weiss and colleagues took their earlier findings a step further. They reported that two sets of pig retroviruses that can infect human cells in vitro are found in a wide variety of pig breeds, including the breeds considered for human transplants. The viruses, PERV-A and PERV-B, contain surface glycoproteins that allow them to infect human cells. The viruses do not make the pigs sick, and the researchers are not sure how they could affect humans.
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