Xenotransplantation is the transplanting of non-human organs into humans.
Since human donor organs for transplantation to patients with failed or failing organs are scarce, xenotransplantation has been considered as an alternative. Pigs are the most likely species to serve as donors for clinical xenotransplantation because of their similarity to humans. The major barrier to transplantation across discordant species, such as from pig to human, is rejection of the graft mediated by xenoreactive natural antibodies that bind the carbohydrate epitope known as alpha-Gal on donor tissues. This DNA is then incorporated into the host cell's genome, where it codes for the synthesis of viral components. The retroviral vectors that are used are altered retroviruses that do not replicate or produce infection, so the retroviruses are merely carriers of genetic material into target cells, where the genetic material is incorporated into the host cell genome.