Thousands of critically-ill people die each year waiting for a suitable organ or tissue donation for transplantation. Pigs offer a potential source of suitably-sized organs for xenotransplantation, the transplantation of living cells, tissues and organs from one species to another species. Xenotransplantation from pigs is currently not feasible because human antibodies react to molecules present on the cell surface of pig tissue to cause the hyperacute response and tissue rejection. Scientists have used a gene-targeting approach to "knockout" the pig genes producing these cell-surface molecules, and have produced cloned pigs that do not have these antigenic molecules on the surface of their cells. Further research to evaluate the survival of transplanted organs from these pigs is underway to evaluate the potential of this technology as a solution for the world-wide shortage of organs and cells for transplantation
