Transplantation: general information

Transplantation can be performed using the patient's own tissues (autotransplantation, for example, bone, skin graft), genetically identical (syngeneic) donor tissues (isotransplantation), genetically different donor tissues (allo- or homotransplantation) and sometimes using transplants from other species animals (xeno- or heterotransplantation). Transplants can be represented by individual cells [such as hematopoietic stem cells (HSC), lymphocytes, pancreatic islet cells], parts or segments of the organs (liver or lung fractions, skin grafts) or whole organs (heart).

Structures can be transplanted to their usual anatomical site (orthotopic transplantation, for example, heart transplantation) or an unusual site (heterotopic transplantation, for example, kidney transplantation into the iliac region). Transplantation is almost always done to improve survival. However, some procedures (transplantation of the tissues of the hand, larynx, tongue, face) provide an improvement in the quality of life, but reduce its duration, and therefore their need is highly controversial.

With the exception of rare cases, allografts of living relatives or unrelated donors, corpse donors are used in clinical transplantology. In living donors, the kidney, GSK, segments of the liver, pancreas, and lung are most often taken. The use of organs from donor corpses (with or without the donor's heart) helps to reduce the discrepancy between the need for organs and their availability; however, the requirements still far exceed resources, and the number of patients waiting for transplantation continues to grow.

Distribution of organs

The distribution of organs depends on the severity of the lesion of certain organs (liver, heart) and the severity of the disease, the time spent on the waiting list, or both of these factors (kidneys, lungs, intestines). In the United States and Puerto Rico, the authorities are firstly distributed across 12 geographical regions, then to local organ procurement organizations. If there are no suitable recipients in one region, the organs are redistributed to recipients in other regions.

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The main principles of transplantation

All recipients of allografts have a risk of rejection; the immune system of the recipient recognizes the transplant as an alien structure and tries to destroy it. In recipients with grafts containing immune cells, there is a risk of developing a "graft versus host" disease. The risk of these complications is minimized through pre-transplantation and immunosuppressive therapy during and after transplantation.

Pre-transplantation screening

Pre-transplantation screening includes the examination of recipients and donors on HLA- (human leukocyte antigen, human leukocyte antigens) and ABO antigens, and recipients also determine sensitivity to donor antigens. HLA-tissue typing is most important in kidney transplantation and the most common diseases in which GSK transplantation is required. Transplantation of the heart, liver, pancreas and lung is usually carried out quickly, often before the HLA-tissue typing is completed, so the importance of pre-transplantation screening for these organs is not so well established.

To select the organ for the most important known determinants of the histocompatibility of the donor and recipient, HLA-tissue typing of peripheral blood lymphocytes and lymph nodes is used. More than 1250 alleles are determined by 6 HLA antigens (HLA-A, -B, -C, -DP, -DQ, -DR), so organ selection is a difficult task; Thus, in the United States only 2 out of 6 antigens coincide on average with the donor and the recipient for kidney transplantation. Selecting an organ with as many matching HLA antigens significantly improves the functional survival of a kidney transplant from a living relative and donor GSK; the successful selection of a transplant for HLA antigens from an unrelated donor also improves its survival, but to a lesser extent because of multiple undetectable differences in histocompatibility. Improvement of immunosuppressive therapy significantly improved the results of transplantation; non-compliance with HLA antigens no longer deprives patients of the possibility of transplantation.

The coincidence of HLA- and ABO-antigens is important for the survival of the graft. A mismatch in ABO antigens can cause acute rejection of well-blood-supplying grafts (kidneys, heart) that have ABO antigens on the cell surface. Previous sensitization to HLA and ABO antigens is a consequence of previous blood transfusion, transplantation, or pregnancies and can be detected by serological tests or more often by lymphocytotoxic tests using the recipient's serum and donor lymphocytes in the presence of components of the complement system. A positive cross-compatibility test indicates that the recipient's serum contains antibodies directed against donor ABO antigens or class I HLA antigens; this is an absolute contraindication for transplantation, with the exception of infants (up to the age of 14 months) who do not yet have isogemagglutinins. Intravenous administration of high doses of immunoglobulin is used to inhibit antigens and promotes transplantation, but long-term results are not yet known. A negative result when checking for cross-compatibility does not guarantee security; when ABO antigens are comparable, but not identical (for example, donor 0 group and recipient A, B or AB group), then due to the production of antibodies to transplanted donor lymphocytes, hemolysis may develop.

Typing for HLA and ABO antigens improves graft survival, but patients with dark skin color are at a disadvantage because they are different from donors with white skin color HLA polymorphism, a higher frequency of pre-sensitization to HLA antigens and blood groups (0 and AT). To reduce the risk of infection before starting the transplantation, it is necessary to exclude possible contact with infectious pathogens and an active infectious process. For this purpose, anamnesis is collected, serological tests for cytomegalovirus, Epstein-Barr virus, herpes simplex virus, varicella and tinea viruses, hepatitis B and C viruses, HIV, tuberculin skin tests are performed. Positive results require post-transplant antiviral therapy (for example, with cytomegalovirus infection or hepatitis B) or rejection of transplantation (for example, if HIV is detected).