Organ transplantation
Organ transplantation is a medical procedure in which an organ is removed from one body and placed in the body of a recipient, to replace a damaged or missing organ. The donor and recipient may be at the same location, or organs may be transported from a donor site to another location. Organs and tissues that are transplanted within the same person's body are called autografts. Transplants that are recently performed between two subjects of the same species are called allografts. Allografts can either be from a living or cadaveric source.
Organs that have been successfully transplanted include the heart, kidneys, liver, lungs, pancreas, intestine, thymus and uterus. Tissues include bones, tendons, corneae, skin, heart valves, nerves and veins. Worldwide, kidneys remain the most commonly transplanted organs, followed by liver and heart. Global analyses indicate that available transplants meet a minority of worldwide need, with the Transplant Observatory reporting substantial gaps between demand and supply and year-to-year increases in registered transplant activity in recent data releases. J. Hartwell Harrison performed the first organ removal for transplant in 1954 as part of the first kidney transplant. Corneae and musculoskeletal grafts are the most commonly transplanted tissues; these outnumber organ transplants by more than tenfold.
Organ donors may be living individuals, or deceased due to either brain death or circulatory death. Tissues can be recovered from donors who have died from circulatory or brain death within 24 hours after cardiac arrest. Unlike organs, most tissues can be preserved and stored—also known as "banked"—for up to five years. Transplantation raises a number of bioethical issues, including the definition of death, when and how consent should be given for an organ to be transplanted, and payment for organs for transplantation. Other ethical issues include transplantation tourism and more broadly the socio-economic context in which organ procurement or transplantation may occur. A particular problem is organ trafficking. There is also the ethical issue of not holding out false hope to patients.
Transplantation medicine is one of the most challenging and complex areas of modern medicine. Some of the key areas for medical management are the problems of transplant rejection, during which the body has an immune response to the transplanted organ, possibly leading to transplant failure and the need to immediately remove the organ from the recipient. When possible, transplant rejection can be reduced through serotyping to determine the most appropriate donor-recipient match and through the use of immunosuppressant drugs.
As of September 9, 2022, the United States reached one million cumulative transplants according to the Organ Procurement and Transplantation Network, with kidneys being the most common globally. Challenges include global shortages, with only 10-20% of needs met, and inequities in access. Recent advances include xenotransplantation, machine perfusion, and normothermic ex-vivo perfusion systems that have extended preservation intervals and improved graft assessment prior to transplant.
Types of transplant
Autograft
Autografts are the transplant of tissue to the same person to minimize rejection. Sometimes this is done with surplus tissue, tissue that can regenerate, or tissues more desperately needed elsewhere. Sometimes an autograft is done to remove the tissue and then treat it or the person before returning it. Autografts involve transplanting tissue within the same individual, such as skin for burns or veins for bypass surgery; rotationplasty relocates a foot/ankle to replace a knee in cancer cases. No immunosuppression needed due to genetic identity.Allograft and allotransplantation
An allograft is a transplant of an organ or tissue between two genetically non-identical members of the same species. Most human tissue and organ transplants are allografts. Due to the genetic difference between the organ and the recipient, the recipient's immune system will identify the organ as foreign and attempt to destroy it, causing transplant rejection. The risk of transplant rejection can be estimated by measuring the panel-reactive antibody level.Isograft
An isograft is a subset of allograft in which organs or tissues are transplanted from a donor to a genetically identical recipient. Isografts are differentiated from other types of transplants because while they are anatomically identical to allografts, they do not trigger an immune response.Xenograft and xenotransplantation
A xenograft is a transplant of organs or tissue from one species to another. An example is porcine heart valve transplant, which is quite common and successful. Another example is attempted piscine–primate transplant of pancreatic islets. The latter research study was intended to pave the way for potential human use if successful. However, xenotransplantation is often an extremely dangerous type of transplant because of the increased risk of non-functional compatibility, rejection, and disease carried in the tissue. In the opposite direction, attempts are being made to devise a way to transplant human fetal hearts and kidneys into animals for future transplantation into human patients to address the shortage of donor organs.Domino transplants
In people with cystic fibrosis, where both lungs need to be replaced, it is a technically easier operation with a higher rate of success to replace both the heart and lungs of the recipient with those of the donor. As the recipient's original heart is usually healthy, it can then be transplanted into a second recipient in need of a heart transplant, thus making the person with CF a living heart donor.In a 2016 case at Stanford Medical Center, a complex set of transplant surgeries involved two patients and three surgical teams. The first patient, a woman with cystic fibrosis, required a heart-lung transplant due to the disease causing one lung to expand and the other to shrink, displacing her heart. Her heart was subsequently donated to a second patient—a woman with right ventricular dysplasia, a condition that caused a dangerously abnormal heart rhythm. The dual procedures also involved a third team responsible for retrieving the heart and lungs from a recently deceased donor. Both recipients recovered well and had the opportunity to meet six weeks after their simultaneous surgeries.
Another example of this situation occurs with a special form of liver transplant in which the recipient has familial amyloid polyneuropathy, a disease where the liver slowly produces a protein that damages other organs. The recipient's liver can then be transplanted into an older person for whom the effects of the disease will not necessarily contribute significantly to mortality.
This term also refers to a series of living donor transplants in which one donor donates to the highest recipient on the waiting list and the transplant center utilizes that donation to facilitate multiple transplants. These other transplants are otherwise impossible due to blood type or antibody barriers to transplantation. The "Good Samaritan" kidney is transplanted into one of the other recipients, whose donor in turn donates his or her kidney to an unrelated recipient. This method allows all organ recipients to get a transplant even if their living donor is not a match for them. This further benefits people below any of these recipients on waiting lists, as they move closer to the top of the list for a deceased-donor organ. Johns Hopkins Hospital in Baltimore and Northwestern University's Northwestern Memorial Hospital have received significant attention for pioneering transplants of this kind. In February 2012, the last link in a record 60-person domino chain of 30 kidney transplants was completed.
In May 2023, New York Presbyterian Morgan Stanley Children's Hospital performed the first domino heart transplantation in a baby, eventually saving two baby girls.
ABO-incompatible transplants
Because very young children do not have a well-developed immune system, it is possible for them to receive organs from otherwise incompatible donors. This is known as ABO-incompatible transplantation. Graft survival and people's mortality are approximately the same between ABOi and ABO-compatible recipients. While focus has been on infant heart transplants, the principles generally apply to other forms of solid organ transplantation.The most important factors are that the recipient not have produced isohemagglutinins, and that they have low levels of T cell-independent antigens. United Network for Organ Sharing regulations allow for ABOi transplantation in children under two years of age if isohemagglutinin titers are 1:4 or below, and if there is no matching ABOc recipient. Studies have shown that the period under which a recipient may undergo ABOi transplantation may be prolonged by exposure to nonself A and B antigens. Furthermore, should the recipient require eventual retransplantation, the recipient may receive a new organ of either blood type.
Limited success has been achieved in ABO-incompatible heart transplants in adults, though this requires that the adult recipients have low levels of anti-A or anti-B antibodies. Renal transplantation is more successful, with similar long-term graft survival rates to ABOc transplants.