Transgenic organs and xenotransplants.

Advances in immunosuppressive treatments reached in the last decades of the 20th century have made solid organ transplantation the treatment of choice for cases of irreversible organ failure. However, the availability of human cadaver organs is limited and the demand for transplants is still on the rise. Also, there is a recognised lack of cells and human tissues for generalised use in transplantation for the treatment of diseases that are characterised by failure of specialised cells (such as pancreatic cells to cure diabetes). Xenotransplantation, which is the transplant of cells, tissues or organs from other species, became the focus of attention in the nineteen-nineties as a solution to the lack of organs and tissues for transplantation. Previous clinical studies using nonhuman primates produced poor outcomes (survival from days to a few months) and confirmed the difficulty of obtaining organs from these species. Since then, progress in xenotransplantation has been slow and still now various immunological and non-immunological barriers need to be overcome. These barriers are reviewed in this chapter and the various approaches explored to date to overcome them, in particular those based on the genetic modification of pigs. Also, cell transplant studies such as those of pancreatic islets in monkeys have led to even more hopeful results. The range of possibilities offered by this technology will be unlimited, making it possible for xenotransplantation to be a clinical reality in a not very distant future.