Organ transplants are viable treatment options for persons with terminal disease of certain organs such as the heart, kidneys, and liver. Except for the surgery, the major problem encountered is that the patient’s lymphoid system recognizes the transplanted organ as foreign and launches an attack against it. The problem is reduced by carefully determining compatibility of the tissues of both donor and recipient. This is usually done by comparing the antigens on the surfaces of leukocytes, called the human leukocyte antigens (HLAs) group A, of donor and recipient. A match does not have to be 100% to make a transplant, but the closer to 100%, the better chance of avoiding rejection.
To overcome the normal immune response and organ rejection, immunosuppressive therapy is administered following transplant surgery. The lymphoid system must be suppressed sufficiently to prevent rejection of the organ but not enough to eliminate immunity against pathogens. Achieving this delicate balance has been aided by the use of cyclosporine, a selective immunosuppressive drug derived from fungi. Cyclosporine inhibits T cell functions but has minimal effects on B cells. Because T cells are primarily responsible for organ rejection, rejection is minimized, and B cells are able to provide antibody-mediated immunity against pathogens. In spite of advances in immunosuppressive therapy, bacterial and viral infections are the primary causes of death among organ transplant recipients. Immunosuppression also increases the risk of cancer.