The future promises of xenotransplantation.

The use of animals as a source of organs and tissues for humans has been an enduring goal of transplantation. Xenotransplantation, as such, would overcome a shortage of human donors and allow for biochemical or genetic approaches to modification of transplants. The use of animal organs and tissue, however, is hindered by an intense immune response of the recipient against the graft. The molecular basis for this immune response has recently been elucidated, at least in part, and specific approaches to therapy, including the genetic engineering of source animals, have been developed. Other hurdles, including the physiologic limitations of the transplant and the possibility of transferring infectious agents from the transplant into the host, may also be important. The development of specific therapies and the application of genetic engineering to overcome these problems can now be envisioned. As the immunologic, physiologic, and infectious hurdles to xenotransplantation are addressed, new efforts will focus on the use of the transplant to impart novel functions to answer the therapeutic needs of the transplant recipient.