Animal Organs in Humans! The Past, Present, and Future of Xenotransplantation


Xenotransplantation is the transplantation of living cells, tissues or organs from one species to another. Such cells, tissues or organs are called xenografts or xenotransplants. This technique is being used around the world in research and is not a sci-fi constructed myth. Mostly this practice is done in lab mice for various research purposes.

The need for such a practice arises from the need to provide organs to patients in need at the right time. Organ shortage causes many deaths the world over. Due to this, the idea of xenotransplantation came about. How great would it be if our organs, rather than sourced from other humans, can be grown in lab animals and then provided to a human recipient when in need? It all sounds tremendous, a scientific breakthrough, a convenient option but here’s the complication; this kind of practice gives rise to many ethical questions.

Brief History

In 2003, mouse embryos were created with human cells in them. Pig embryos injected with human stem cells have been tried by scientists. In the 1920s, monkey testicles and later on goat testicles were transplanted into human men. Chimpanzee kidneys have been transplanted into humans in the 1960s. In the 1980s, attempts at making chimeras resulted in a “geep”, goat and sheep embryos combined to make a half goat half sheep.


Chimeras are organisms that result from putting two different organisms together. In more detail, an animal chimera is a single organism that is composed of two or more different populations of genetically distinct cells that originated from different zygotes involved in sexual reproduction.  The 1990s brought with it a monkey heart and later a baboon liver being transplanted into humans and the successful cloning of Dolly the sheep.

There are many such examples in history where scientists, researchers, and doctors have tried their hand at xenotransplantation. Attempts at this technique date back to as early as 1905 when slices of rabbit kidney were transplanted into a child with renal issues. All of the above attempts have either failed, not resulted in the desired effects, caused the death of the human and almost always condemned on the basis of ethics.

That said, this procedure may in itself be condemnable and raise questions but it could be the stepping stone for developing procedures that are successful and do not give rise to any ethical debates such as growing human organs in the lab.

Implications of Xenotransplantation

Despite many organ donation drives worldwide, shortage of transplantable organs causes 20-35% deaths of patients who are in dire need of a donor’s organ but cannot receive one on time. Xenotransplantation sans the ethical issues can save millions of patients’ lives.

A xenotransplant could be done readily and would not involve any waiting lists or endanger patients’ lives because of a lack of available organs. The procedure theoretically involves acquiring organs from animals and genetically altering them with human genes. This is important in order for our immune system to accept the organ as a part of the human body rather than a foreign object. Many transplants result in organ rejection by the body, even if the organ is donated by another human being. Thus, xenotransplantation theoretically seems to be the answer to the problem of organ shortage.

Hurdles in the Way of Successful Xenotransplantation

Ethical Issues in Xenotransplantation
Many ethical issues are raised when it comes to Xenotransplantation.

In theory, the path to the success of xenotransplants seems hunky dory but in reality, there are many problems involved in this procedure. Some of them are mentioned below:

  • Xenotransplants require suitable animal donors compatible with humans. The first choice that comes to mind is non-human Primates. Since humans are primates too, it seems to be the animal of choice for a procedure involving humans. Their organs are almost the same size as humans and their blood chemistry is compatible too. Gorillas, chimpanzees, orangutans, lemurs, baboons, apes are some examples of primates. Among these examples, chimpanzees were originally considered as the best option but as they were declared endangered, they were taken off the list of potential donors. All other primates either have small size organs or have blood type compatibility issues.
  • Numerous diseases can be transferred from animals to humans during this procedure. Many viruses and diseases affecting animals do not affect humans because of many barriers present between animal and human bodies. When this barrier no longer exists, which happens in the case of transplantation, animal diseases can easily be transferred via the donated organ to the human recipient. This occurrence is called xenozoonosis. It is the transfer of an infectious disease from animal to human by transplantation of an animal tissue or organ into the human body.
  • The difference in time and speed of aging of animal and human cells is another problem in the way of successful xenotransplantation. The average life span of humans and animals is different and some scientists believe this could affect the functionality of the donated organs. They may not function after they are over their lifespan.
  • Immune system rejection of donated organs is a problem even when human organs are transplanted into patients. Such a transplantation where organs are transplanted from donors of the same species is called allotransplantation. Xenotransplants, in contrast, can not only result in immune system rejection, the reaction of the body to such transplants is often more adverse and severe as compared to allotransplants. The patient can even die immediately from this transplant. Such is the intensity of xenotransplantation complexities in humans.
  • Transplantable organs need to be of the same size as human organs, they should function exactly the same way as human organs, the hormones and protein production inside donor animals needs to be the same as humans, and most importantly, the body temperature of the donor animal needs to be similar to humans. These physiological factors play a vital role in rejection or acceptance of the donor organ. Although Pigs are considered the best donors for xenotransplantation at the moment, their body temperature is 2 degrees Celsius above that of humans. Even a small difference in body temperature affects how organs function. When we have a fever, our organs cannot function how they normally do. Although substantial research has not been done on this aspect, in theory, such a difference can be hazardous to the health of the recipient.
  • The animals which are supposed to be used for such experiments either become disfigured or die during lab tests. This has very often given rise to trouble from animal-rights groups. This procedure is considered synonymous to animal cruelty.
  • Perhaps the biggest hurdle in the way of research of this procedure is the ethical side of the matter. The instance of mouse embryos created with human cells inside, though a success, raised questions regarding reproduction of such mice. What if such mice mate? What will be the resulting progeny like? What if absurd chimeras are born with human features in lab rats! Ethical issues have shut down the majority of such controversial research and for good measure.