Organ transplantation is a medical process 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/or tissues that are transplanted within the same person’s body are called autografts.
Transplants between two individuals 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.
Tissue transplants include bones, tendons (musculoskeletal grafts), corneae, skin, heart valves, nerves and veins.
Worldwide, the kidneys are the most commonly transplanted organs, followed by the liver and then the heart.
Corneae and musculoskeletal grafts are the most commonly transplanted tissues; these outnumber organ transplants by more than tenfold.
Organ donors may be living, brain dead, or dead via circulatory death.
Tissue may be recovered from donors who die of circulatory death, as well as of brain death for up to 24 hours past the cessation of heartbeat.
Most tissues, with the exception of corneas, and unlike organs, can be preserved and stored for up to five years: banked.
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.
Autografts are the transplant of tissue to the same person: this is done with surplus tissue, tissue that can regenerate, or tissues more desperately needed elsewhere (examples include skin grafts, vein extraction for CABG.
In a rotationplasty, a distal joint is used to replace a more proximal one; typically a foot or ankle joint is used to replace a knee joint.
The person’s foot is severed and reversed, the knee removed, and the tibia joined with the femur.
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.
Because of 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.
An isograft is a subset of allograft in which organs or tissues are transplanted from a donor to a genetically identical recipient (identical twin).
Isografts do not trigger an immune response.
A xenograft is a transplant of organs or tissue from one species to another: An example is porcine heart valve transplant, piscine–primate (fish to non-human primate) transplant of pancreatic islets.
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.
Domino transplant: In people with cystic fibrosis (CF), 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.
The recipient’s original heart is usually healthy, and can then be transplanted into a second recipient in need of a heart transplant, thus making the person with CF a living heart donor.
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.
This method allows all organ recipients to get a transplant even if their living donor is not a match for them.
Very young children (generally under 12 months, but often as old as 24 months do not have a well-developed immune system, and it is possible for them to receive organs from otherwise incompatible donors: this is known as ABO-incompatible (ABOi) transplantation.
Graft survival and people’s mortality are approximately the same between ABOi and ABO-compatible (ABOc) recipients.
At this age recipients have not have produced isohemagglutinins, and that they have low levels of T cell-independent antigens.
People with obesity are no longer considered inappropriate candidate donors or recipients for renal transplantation.
Human herpesvirus 6 (HHV-6) reactivation is a notable concern in pediatric liver transplantation, potentially influencing both graft and recipient health.
HHV-6, prevalent in a substantial portion of the population, can manifest in liver transplant recipients with inherited chromosomally integrated HHV-6 (iciHHV-6), predisposing them to heightened risks of complications such as graft-versus-host disease and allograft rejections.
Kidney transplantation is becoming increasingly common and is the preferred treatment for end-stage renal failure.
Liver transplantation is the only curative therapy for end-stage liver disease, and the liver is the second most frequently transplanted solid organ.
Pancreatic transplantation is a complex surgical procedure performed in patients with severe chronic diabetes, often in association with renal transplantation.
Heart transplantation is increasingly performed in patients with end-stage heart failure, most often related to ischemic and non-ischemic cardiomyopathies.
The main complications of transplantation are procedural complications, infection, acute rejection, cardiac allograft vasculopathy and malignancy.
Non-vascular and vascular complications can occur in the initial post-transplant phase and at later stages.
Overall postoperative complications after kidney transplantation occur in approximately 12% to 25% of kidney transplant patients.
Organ donors may be living or may have died of brain death or circulatory death.
Most deceased donors are those who have been pronounced brain dead.
Brain dead is the cessation of brain function, typically after receiving an injury to the brain, or otherwise cutting off blood circulation to the brain.
Breathing is maintained via artificial sources, which, in turn, maintains heartbeat.
Once brain death has been declared, the person can be considered for organ donation.
Fewer than 3% of all deaths in the US are the result of brain death, meaning the overwhelming majority of deaths are ineligible for organ donation, resulting in severe shortages.
Patients that have been pronounced brain dead are one of the most common and ideal donors, since often these donors are often young and healthy, thus leading to high quality organs.
Organ donation is possible after cardiac death in some situations, primarily when the person is severely brain-injured and not expected to survive without artificial breathing and mechanical support.
Independent of any decision to donate, a person’s next-of-kin may decide to end artificial support.
If the person is expected to expire within a short period of time after support is withdrawn, arrangements can be made to withdraw that support in an operating room to allow quick recovery of the organs after circulatory death has occurred.
Tissues may be recovered from donors who die of either brain or circulatory death.
In general, tissues may be recovered from donors up to 24 hours past the cessation of heartbeat.
In contrast to organs, most tissues, except corneas, can be preserved and stored for up to five years.
More than 60 grafts may be obtained from a single tissue donor.
Due to the ability to recover from a non-heart-beating donor, the ability to bank tissue, and the number of grafts available from each donor – tissue transplants are much more common than organ transplants.
More than one million tissue transplants take place in the United States each year.
In living donors, the donor remains alive and donates a renewable tissue, cell, or fluid-blood, skin), or donates an organ or part of an organ in which the remaining organ can regenerate or take on the workload of the rest of the organ- single kidney donation, partial donation of liver, lung lobe, small bowel.
Deceased donors are people who have been declared brain-dead and whose organs are kept viable by ventilators or other mechanical mechanisms until they can be excised for transplantation.
Apart from brainstem-dead donors, who have formed the majority of deceased donors for the last 20 years, there is increasing use of after-circulatory-death donors to increase the potential pool of donors as demand for transplants continues to grow.
Prior to the legal recognition of brain death, all deceased organ donors had died of circulatory death.
These organs have inferior outcomes to organs from a brain-dead donor.
Patients who underwent liver transplantation using donation-after-circulatory-death allografts have been shown to have significantly lower graft survival than those from donation-after-brain-death allografts due to biliary complications and primary nonfunction in liver transplantation.
Rare.y, a directed or targeted donation, in which the family of a deceased donor requests an organ be given to a specific person, subverting the allocation system.
A paired-exchange is a technique of matching willing living donors to compatible recipients using serotyping:may more efficiently allocate organs and lead to more transplants.
Good Samaritan, altruistic donation, is giving a donation to someone that has no prior affiliation with the donor.
The idea of altruistic donation is to give with no interest of personal gain, it is out of pure selflessness.
In compensated donation, donors get money or other compensation in exchange for their organs.
In the United States, The National Organ Transplant Act of 1984 made organ sales illegal.
The World Medical Association: prisoners and other individuals in custody are not in a position to give consent freely, and therefore their organs must not be used for transplantation.
Muslims believe body desecration in life or death to be forbidden, and thus many reject organ transplant.
With regard to organ transplantation in Israel, there is a severe organ shortage due to religious objections by some rabbis who oppose all organ donations and others who advocate that a rabbi participate in all decision making regarding a particular donor.
One-third of all heart transplants performed on Israelis are done in China; others are done in Europe.
By September 2022, the US had reached one million organ transplants overall.
The rising success rate of transplants and modern immunosuppression make transplants more common, the need for more organs has become critical.
Researchers have been looking into means of reducing the general burden of immunosuppression: Approaches in reducing burden include avoidance of steroids, reduced exposure to calcineurin inhibitors, and other means of weaning drugs based on patient outcome and function.
Reduced immunosuppression increases the risk of rejection and decreases the risk of infection.
In the United States, tissue transplants are regulated by the US Food and Drug Administration (FDA) which sets strict regulations on the safety of the transplants, primarily aimed at the prevention of the spread of communicable disease.
Regulations include criteria for donor screening and testing as well as strict regulations on the processing and distribution of tissue grafts.
Organ transplants are not regulated by the FDA.
It is essential that the HLA complexes of both the donor and recipient be as closely matched as possible to prevent graft rejection.
Hypothermic perfusion is in clinical use for transplantation of kidneys and liver, while normothermic perfusion has been used effectively in the heart, lung, liver and, less so, in the kidney.