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  1. Robin A Weiss, professor of viral oncology
  1. Institute of Cancer Research, Chester Beatty Laboratories, London SW3 6JB.

    Imagine that your patient needs a transplant, say a new heart. A specially bred pig carrying human genes may soon supply it. That is the hope and hype of xenotransplantation, the transfer of animal cells, tissues, and organs to humans. Xenotransplantation is not entirely novel, as pig heart valves have been used for many years without apparent ill effect, but they are essentially inert tissue and seldom elicit rejection. There is now considerable excitement that the transplantation of live animal tissues may soon become a practical treatment option, although this is matched by concern over the risk of new zoonotic infections in transplant recipientsh.1 This article discusses the potential and the problems of xenotransplantation and explains why it faces an uncertain future.

    Summary points

    Transplantation of pig cells and tissues to treat diabetes and degenerative conditions such as Parkinson's disease and Huntington's chorea will become more common

    Whole organ transplants from genetically modified pigs could make up the shortfall in human organs if immunological and physiological barriers can be overcome

    Xenografts might be used as “bridging” organs to keep patients alive until human organs become available

    The risk of zoonotic infections in xenotransplant recipients and their possible spread in the human population cannot be ignored—HIV and new influenza strains are thought to have started as zoonoses before becoming human pandemics

    Clear ethical, safety, and monitoring guidelines are needed to control the development of xenotransplantation

    Meeting the need

    Figure 1shows the imbalance between the supply and demand for organ transplants, with the largest waiting by far being for kidney transplants. Furthermore, the need for organ donors will continue to rise as more patients and new diseases are deemed eligible for treatment by transplantation. Even if opt out policies were adopted (in which people are assumed to consent unless they state otherwise) the supply of …

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