@oristarA,
Because at the begining, the author says:
Clinical xenotransplantation: the next medical revolution?
Burcin Ekser, Mohamed Ezzelarab, Hidetaka Hara, Dirk J van der Windt, Martin Wijkstrom, Rita Bottino, Massimo Trucco, David K C Cooper
The shortage of organs and cells from deceased individuals continues to restrict allotransplantation. Pigs could provide an alternative source of tissue and cells but the immunological challenges and other barriers associated with
xenotransplantation need to be overcome.
Transplantation of organs from genetically modified pigs into non-human primates is now not substantially limited by hyperacute, acute antibody-mediated, or cel lular rejection, but other issues have become more prominent, such as development of thrombotic micro angiopathy in the graft or systemic consumptive coagulopathy in the recipient. To address these problems, pigs that express one or more human thromboregulatory or anti-infl ammatory genes are being developed. The results of preclinical transplantation of pig
cells—eg, islets, neuronal cells, hepatocytes, or corneas—are much more encouraging than they are for organ
transplantation, with survival times greater than 1 year in all cases. Risk of transfer of an infectious microorganism to
the recipient is small.