What is Xenotransplantation?
Most of us know about human organ transplant. A surgeon replaces a failing organ with a healthy organ from another person. Sounds easy enough but the problem is that, human organs are always out of stock. So we turn our need to the other species in the evolutionary tree.
Xenotransplantation, as defined by the World Health Organization, is a living cell, tissue, or organ transplant between two different species such as pigs to humans. It was derived from the Greek word xenos- which means “foreign.” Xenotransplantion dates back more than 100 years ago. During the early 1900, the first few attempts of xenotransplant use organs from pig, goat, sheep, and monkey but were unsuccessful and patients only last for several hours or days. In 1963, chimpanzee kidney transplants were performed to 13 patients and only one survived for 9 months. A modified pig liver was used temporarily in 1997 to keep a patient alive until a suitable liver becomes available. Also in 1997, xenotransplantation was banned worldwide due to a high risk of infectious disease from animals but was lifted later on and today, clinical trials for xenotransplantation continues.
Xenotransplantation is important because it can potentially benefit thousands of patients. It can provide unlimited supply of cells, tissues, and organs. It can replace diseased organs such as heart, lungs, liver, pancreas, and kidney. It can replace damaged cells from diabetes, Alzheimer’s, and Parkinson’s disease. It can be used for skin grafts, cornea transplant, or bone transplant. It can provide temporary external organ function to patient with organ failure.
One problem that can be solved with xenotransplantation is the shortage of human organs. According to DonorOrgan.gov, there are 113,000+ patients awaiting organ transplant in the United States last year. From the waiting list, only 29% received organ transplant. On average, 20 people die everyday waiting for a donor. The waiting list will continue to grow as one person is added to the list every 10 minutes.
Currently, the best candidates for xenotransplantation donor are the pigs. Chimpanzees are thought to be the best option since they are closely related to humans. Chimpanzee organs are similar in size and there blood type is compatible to humans. The only problem is that Chimpanzees are endangered species. Baboons were also considered as organ donors but they have smaller body size, infrequent type O blood (the universal donor), and they do not produce a lot of offspring. The major problem in using non-human primates is the risk of disease transmission because they are so closely related to humans according to the Phylogenetic tree. Pigs on the other hand are distant to humans which lowers the risk of disease transmission. As we know, pigs are readily available and there organs are comparable in size. There is less likely for a new infectious agent to develop because pigs are always in close contact with humans through domestication.
The development of xenotransplantation comes with barriers, issues, and concerns. The human immune system itself is the major obstacle for the success of xenotransplantation. Normally, the inside of our body destroys anything that is foreign. Since animal organs are foreign, the human immune system will attack the transplanted organ which leads to fatal infection. Extensive research is still needed on whether animal organs can replace the physiological function of human organs. Pigs can only live for roughly 15 years and we do not know if there organs can last longer than that. Human hormones and proteins are different from pigs and can cause malfunction of regulatory processes. Pigs have a higher body temperature than humans and the implications for the difference is still unknown. Lastly, xenotransplantation is a very controversial procedure since the beginning and many animal rights group opposed killing animals to harvest their organs for human use.
In summary, no xenotransplantation has been successful for the last 100 years due to a number of obstacles and the development is only driven by the number of demand for human organs far exceeds the supply, but if successful, the benefits and resources are considerable. Since human organs are always out of stock, state government are already stepping in by considering a policy that makes everyone an organ donor by default.
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