Xenotransplantation

Xenotransplantation (xenos- from the Greek meaning "foreign" or strange), or heterologous transplant, is the transplantation of living cells, tissues or organs from one species to another. Such cells, tissues or organs are called xenografts or xenotransplants. It is contrasted with allotransplantation (from other individual of same species), syngeneic transplantation or isotransplantation (grafts transplanted between two genetically identical individuals of the same species), and autotransplantation (from one part of the body to another in the same person).^{[citation needed]} Xenotransplantation is an artificial method of creating an animal-human chimera, that is, a human with a subset of animal cells. In contrast, an individual where each cell contains genetic material from a human and an animal is called a human–animal hybrid.

Patient derived xenografts are created by xenotransplantation of human tumor cells into immunocompromised mice, and is a research technique frequently used in pre-clinical oncology research.

Human xenotransplantation offers a potential treatment for end-stage organ failure, a significant health problem in parts of the industrialized world. It also raises many novel medical, legal and ethical issues. A continuing concern is that many animals, such as pigs, have a shorter lifespan than humans, meaning that their tissues age at a quicker rate. (Pigs have a maximum life span of about 27 years.) Disease transmission (xenozoonosis) and permanent alteration to the genetic code of animals are also causes for concern. Similarly to objections to animal testing, animal rights activists have also objected to xenotransplantation on ethical grounds. A few temporarily successful cases of xenotransplantation are published.

Bioprosthetic artificial heart valves are generally pig or bovine-derived, but the cells are killed by glutaraldehyde treatment before insertion, therefore technically not fulfilling the WHO definition of xenotransplantation of being live cells.

The first serious attempts at xenotransplantation (then called heterotransplantation) appeared in the scientific literature in 1905, when slices of rabbit kidney were transplanted into a child with chronic kidney disease. In the first two decades of the 20th century, several subsequent efforts to use organs from lambs, pigs, and primates were published.

Scientific interest in xenotransplantation declined when the immunological basis of the organ rejection process was described. The next waves of studies on the topic came with the discovery of immunosuppressive drugs. Even more studies followed Joseph Murray's first successful renal transplantation in 1954 and scientists, facing the ethical questions of organ donation for the first time, accelerated their effort in looking for alternatives to human organs.

On February 16, 1963, the first transplant of a non-human animal's organ into a human being took place in Minneapolis when surgeons led by Dr. Claude R. Hitchcock and R. Joseph Kiser "tried grafting a baboon kidney" into "a woman in whom previously implanted human kidney (from a corpse) was doing poorly", and the kidney "immediately began functioning normally and cleared her blood of wastes". Her body rejected the kidney five days afterward and she died in March, three weeks later.

Starting in October 1963, doctors at Tulane University attempted renal transplantations from non-human primates in six people who were near death. The first person, a 32 year old woman with a chronic kidney disease received the kidneys of a rhesus monkey and the kidneys "functioned well for seven days, then failed," and the patient died later from her illness. The first successful attempt (one in which the patient was able to leave the hospital and return home) with a chimpanzee was performed on November 5 at Charity Hospital in New Orleans by a 12-man team of Tulane physicians, led by Dr. Keith Reemtsma, and the patient, a 44-year-old dock worker named Jefferson Davis, left the hospital on December 17 after a six-week recuperation.; after this and several subsequent unsuccessful attempts to use primates as organ donors and the development of a working cadaver organ procuring program, interest in xenotransplantation for kidney failure dissipated. Out of 13 such transplants performed by Keith Reemtsma, one kidney recipient lived for nine months.