The main failure of transplantation is rejection of a grafted organ or tissue because of genetic differences between a recipient and a transplant. The transplant becomes “foreign” to recipient’s organism. It is believed that transplant contains antigens, which causes a rejection reaction in recipient’s organism.
Failures of autogenous or isogenous transplantations are determined not only by immune but also by other factors: surgery technique, bloodstream disorders, infections. Successful homogeneous transplantation is more frequent between blood relatives: parents, brothers, sisters, cousins. Without special treatment with drugs and other measures results of heterogeneous transplantations are rarely positive. An exception is for nonvascular (without blood vessels) transplants when there is little relation with transplant antigens (e.g. transplantation of porcine heart valves to a human).
The reaction of grafted organ rejection may be of two directions:
- Recipient’s organism recognises the transplant as a foreign body and tries to destroy it;
- Cells of the transplant immune system recognise recipient’s organism as a foreign body and disturb accretion of an organ.
Immune response is decreased by prescribing different medicaments (immunsuppresant drugs, corticosteroids, cytostatics), which block reactions of transplant rejection.