PPL Therapeutics announced this week that on Christmas Day five genetically modified and cloned Pigs were born that bring the possibility of Xenotransplantation — transplanting organs from animals to human beings — one step closer.
The pigs are genetically modified to make it more likely that an organ transplanted to human beings would not be rejected by the human immune system. Researchers knocked out a gene in the pigs that produces an enzyme that adds a sugar to the surface of the cells. This sugar would be identified immediately by the human immune system which result in an attack and the rejection of the organ.
Which does not mean that organs from these genetically modified pigs are ready to be transplanted into humans. In fact, another gene that performs a similar function would have to be knocked out as well as several human genes added in order for there to be a reasonable chance at transplanted organs not being rejected.
Still, PPL Therapeutics vice-president David Ayares told New Scientist that he hopes human trials could begin within five years. Pigs, by the way, would be ideal for heart transplants since the heart in this particular species of pig is roughly the same size as the human heart.
Since the pigs were cloned, PPL Therapeutics would have the ability to quickly ramp up production of replacement organs should their technology eventually succeed in human trials.
Of course, the animal rights community is opposed to this, with the Campaign for Responsible Transplantation once again raising the red flag about possible pig viruses being passed on to human beings. CRT has spent the last couple of years arguing that the possibility of cross-infection of porcine endogenous retrovirus should lead to an outright ban of xenotransplantation with pigs.
In 1997, researchers proved that, at least in laboratory conditions, PERV could jump from pig cells to human cells. PPL Therapeutics and other companies hoping to market this technology will likely have to create pigs that are free from PERV. The PERV virus has been completely sequenced and patented, however. Another company, Immerge, has bred pigs which it says are genetically modified so they cannot pass along PERV to human beings.
Which is largely irrelevant to the animal rights activists, for whom the argument is largely a smokescreen. Wired, for example, cites an earlier interview with CRT’s Alix Fano in which Fano said,
Every animal has hundreds of retroviruses, and there’s no way you can breed them out. And there could be other viruses lurking in these pigs, not to mention parasites, bacteria, fungi and latent infections of all kind.
Of course if medical technologies are required to meet a criteria of eliminating unknown fears and possibilities, then a lot more has to go out the window than just xenotransplantation. For example, pig heart valves are currently used in valve replacement surgery — and with no reports of cross contamination of pig viruses, parasites, etc. to my knowledge.
Ironically, Dr. Jay Fishman, who sequenced the PERV disease, presented a paper in May 2000 noting that organs transplanted from animals to humans might actually turn out to be safer because common human diseases that cause organ failure would likely not grow in organs transplanted from another species. Wired quotes Fishman as writing in that paper,
Due to the species differences between the host (human) and donor (non-human species), the risk of infection of the transplanted organ … may actually be decreased. This incudes common pathogens such a cytomegalovirus, Epstein-Barr virus, … herpes, hepatitis B and C, and possibly human immunodeficiency viruses.
Sources:
Cloned pigs as organ donors?. Kristen Philipkoski, Wired, January 3, 2002.
Knock-out pig clones advance transplant hopes. Emma Young, New Scientist, January 3, 2002.
Animal transplants: a step closer?. The BBC, January 3, 2002.
New pig clones born. The BBC, January 2, 2002.