What is Xenotransplantation?
A patient whose failing heart had been replaced with the heart of a genetically altered pig in a landmark surgery at the University of Maryland Medical Centre in Baltimore, United States, died recently, two months after the operation.
What is Xenotransplantation?
- According to the FDA, xenotransplantation is “any procedure that involves the transplantation, implantation or infusion into a human recipient of either (a) live cells, tissues, or organs from a nonhuman animal source, or (b) human body fluids, cells, tissues or organs that have had ex vivo contact with live nonhuman animal cells, tissues or organs”.
- Xenotransplantation is seen as an alternative to the clinical transplantation of human organs whose demand around the world exceeds supply by a long distance.
- Xenotransplantation, if found compatible in the long run, could help provide an alternative supply of organs to those with life-threatening diseases.
- Xenotransplantation involving the heart was first tried in humans in the 1980s.
- A well known case was that of an American baby, Stephanie Fae Beauclair, better known as Baby Fae, who was born with a congenital heart defect, and who received a baboon heart in 1984.
Why the heart of a pig?
- Pig heart valves have been used for replacing damaged valves in humans for over 50 years now. There are several advantages to using the domesticated or farmed pig (Sus scrofa domestica) as the donor animal for xenotransplantation.
- The pig’s anatomical and physiological parameters are similar to that of humans, and the breeding of pigs in farms is widespread and cost-effective.
- Also, many varieties of pig breeds are farmed, which provides an opportunity for the size of the harvested organs to be matched with the specific needs of the human recipient.
Genetically engineered pig
- The molecular incompatibility between pigs and humans can trigger several immune complications after the transplant, which might lead to rejection of the xenograft.
- To preempt that situation, genetic engineering is used to tweak the genome of the pig so as to ‘disguise’ it, so that the immune system of the human recipient fails to recognise it, and the reactions that lead to xenograft rejection are not triggered.
- In the case of Bennett, the donor pig had been put through 10 genetic modifications intended to ‘deactivate’ or knock out four pig genes, and add six human genes. A “GalSafe” pig was used, from which a gene that codes for Alpha-gal (a sugar molecule) was removed. Alpha-gal can elicit a devastating immune response in humans, and GalSafe pigs have been well studied, and are approved by the USFDA for use in pharmacology.
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