In theory, xenotransplantation could be viewed as a life-saving answer for many awaiting organ transplants, and for doctors dealing with organ shortages. However, the use of animal organs for human transplants has been under scrutiny since the inception of the idea, due to the many risks involved, not only to the patient but the general public, and bioethics issues pertaining to the use of animals for human advancement.
Several years ago it appeared the main roadblock to using pig organs for xenotransplantation was the presence of galactosyl (GAL) moeties linked to the cell surfaces of animal tissues, and produced by the enzyme alpha-galactosyl transferase. Primates, including humans, do not have GAL-linkages on their cell surfaces and produce antibodies against them, causing the rejection of transplanted animal organs. It has since been established that the causes for organ rejection are more complicated than that, and additional antigens have been implicated in the human immune system response. However, immunological issues remain the main roadblocks to xenotransplantation, according to Dr. Muhammad Mohiuddin of the NIH Cardiothoracic Surgery Research Program, National Heart, Lung, and Blood Institute.
In addition to the immunological issues, there are safety concerns for whole populations, due to the possibility of infection of an organ recipient by an animal virus, and animal rights issues, that result in ethical debate over the topic of xenotransplantation. As a result, there are also many regulatory hurdles to overcome, before xenotransplantation becomes everyday practice.
Transplants of animal organs to humans is obviously performed at the expense of the animal in question. Animal rights advocates believe that it is not morally acceptable to sacrifice animals for the benefit of human lives, whether for the use of their organs or for research necessary to study the immunological factors causing organ rejection.
Humans are not without risk in this issue either. The effects latent animal viruses will have on human organ recipients, are still unknown. Opponents of xenotransplantation fear that these viruses, when introduced into a human system might cause epidemics of diseases for which we have no immunity and no cure. Pigs, for example, currently the best candidate animal species for culturing organs for humans, carry a retrovirus called PERV (Porcine Enogenous Retrovirus). This virus has been shown to infect human cells and the consequences of infection have not yet been determined.
Some opponents of xenotransplantation believe that animals are not the solution but that biotech companies are just looking to make money from their ability to clone animal cells and create GMOs, specifically GM pigs (knockouts lacking the alpha-galactosyl transferase enzyme).