immunology allergic disorders
Overview of Transplantation
Introduction
Transplants may be The patient’s own tissue (autografts; eg, bone, bone marrow, and skin grafts) Genetically identical (syngeneic [between monozygotic twins]) donor tissue (isografts) Genetically dissimilar donor tissue (allografts, or homografts) Rarely, grafts from a different species (xenografts, or heterografts) Transplanted tissue may be Cells (as for Hematopoietic Stem Cell Transplantation [HSC] transplants, lymphocyte transplants, and Parts or segments of an organ (as for Liver Transplantation or pulmonary lobar transplants and Entire organs (as for Heart Transplantation , Tissue Transplantation (eg, composite tissue grafts, Tissues may be grafted to an anatomically normal site (orthotopic; eg, heart transplants) or abnormal site (heterotopic; eg, a kidney transplanted into the iliac fossa). Almost always, transplantation is done to replace or restore the function of an end-stage diseased organ, thereby restoring an essential function and improving patient survival. However, some procedures (eg, hand, larynx, tongue, uterus, facial transplantation) enhance the quality of life but do not improve survival and have significant risks related to surgery and immunosuppression. Some of these procedures are highly specialized and done infrequently but are no longer considered experimental. Clinical transplantation uses allografts from donors who are Living and related to the patient Living and unrelated to the patient Deceased Living donors are often used for kidney and hematopoietic stem cell transplants, less frequently for segmental liver transplants, and rarely for pancreas and lung transplants. Use of deceased-donor organs (from heart-beating or non–heart-beating donors) has helped reduce the disparity between organ demand and supply; however, demand still far exceeds supply, and the number of patients waiting for organ transplants continues to grow. Some research is ongoing in transplantation of non-human organs, such as heart, kidney and liver transplantation. Despite progress in the field, clinical implementation is still delayed, mainly due to insurmountable rejection, but also due to critical functional differences between xenografts and human tissue. 