by Tracy Blankenship

Created on: September 03, 2009

What is xenotransplantation?

A current statistic states that every day ten people die while waiting for donor organs for transplantation. This crushing need has for years, driven research into the possibility of using animal organs to replace human ones. This is called xenotransplantation.

According to the US Food and Drug Administration (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." A simpler definition is a transplant into a human using non-human living tissue.

The key term here is "living tissue". Currently, heart valves from pigs and tissue from cows are routinely implanted into humans, the critical difference being these are chemically treated to render them inert, thereby not activating the body's immune system.

To the baby boomer generation, the experience of Baby Fae is the most well-known example. Baby Fae was born in 1984 with a severe heart defect which was inoperable. Surgeons at Loma Linda University Medical Center harvested a heart from a baboon and implanted it into Baby Fae. She lived only a few weeks, dying ultimately from infection. She was not the first recipient of an animal organ.

Xenografts were first introduced around the turn of the century, when a few pioneering souls crafted the mechanical techniques of matching up arteries and veins. A few years later surgeons attempted the first kidney xenografts, with dire results. Because the immune response was still largely unknown, most grafts failed immediately, or within days.

Infection and tissue rejection are still the main roadblocks in the progress of xenotransplantation. Progress in reducing tissue rejection has made "homografts" (same species, i.e. human-human) like kidneys a routine, if scarce, treatment option, but this has come after years of on-going research.

To further complicate xenotransplantation, the emergence of trans-species infection, (think swine flu, bird flu, AIDS) has created a whole new set of problems to consider. If these organisms can breach our natural defenses, what havoc might they wreak when unknowingly introduced, perhaps even inserting into our genome?

Donor animals that might be closest to us genetically, the primates, have been historically considered for donor organs. What isn't stated but is implicit is that the donor animal is sacrificed, leading more and more to question the ethics of using a life form so similar to our own. Using pigs seems to cause less ethical discomfort. Advances in genetic engineering have led to promising discoveries such as pigs which are lacking in the substances that provoke certain stages of the immune response.

Today xenotransplantation remains an experimental, end-of-life stop-gap measure, the future of which is anything but clear.

Learn more about this author, Tracy Blankenship.
Click here to send this author comments or questions.