Types of transplant
Autografts are the transplant of tissue to the same person. Sometimes this is done with surplus tissue, tissue that can regenerate, or tissues more desperately needed elsewhere (examples include skin grafts,
vein extraction for CABG, etc.). Sometimes an autograft is done to remove the tissue and then treat it or the person before returning it (examples include stem cell autograft and storing blood in advance of surgery). In a rotationplasty, a 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.
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.
A subset of allografts in which organs or tissues are transplanted from a donor to a genetically identical recipient (such as an identical twin). 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 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 (fish to non-human primate) transplant of islet (i.e. pancreatic or insular tissue) tissue. The latter research study was intended to pave the way for potential human use if successful. However, xenotransplantion is often an extremely dangerous type of transplant because of the increased risk of non-compatibility, rejection, and disease carried in the tissue. In an opposite twist, Ganogen Research Institute CEO Eugene Gu is studying how to transplant human fetal hearts and kidneys into animals for future transplantation into human patients to address the shortage of donor organs.
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. 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 woman who was needing a heart-lung transplant had cystic fibrosis which had led to one lung expanding and the other shrinking thereby displacing her heart. The second patient who in turn received her heart was a woman with right ventricular dysplasia which had led to a dangerously abnormal rhythm. The dual operations actually required three surgical teams including one to remove the heart and lungs from a recently deceased initial donor. The two living recipients did well and in fact had an opportunity to meet six weeks after their simultaneous operations.
Another example of this situation occurs with a special form of liver transplant in which the recipient suffers from familial amyloidotic 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. Depending on the person on the waiting list, this has sometimes been repeated for up to six pairs, with the final donor donating to the person at the top of the list. This method allows all organ recipients to get a transplant even if their living donor is not a match to 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 Medical Center 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.
Because very young children (generally under 12 months, but often as old as 24 months,) 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 (ABOi) transplantation. Graft survival and people's mortality is approximately the same between ABOi and ABO-compatible (ABOc) 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 (UNOS) 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 (for example, type B-positive with a type AB-positive graft) 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.
Transplantation in obese individuals
Until recently, people labeled as obese were not considered appropriate candidates for renal transplantation. In 2009, the physicians at the University of Illinois Medical Center performed the first robotic renal transplantation in an obese recipient and have continued to transplant people with Body Mass Index (BMI)’s over 35 using robotic surgery. As of January 2014, over 100 people that would otherwise be turned down because of their weight have successfully been transplanted.