Organ transplantation is surgery in which a diseased or damaged organ is removed from a patient and replaced with a healthy organ from an organ donor. All major organs, including the heart, lungs, liver, and kidneys, can be transplanted, and the success rate ranges from 90% to 50%, depending upon the organ transplanted. In the United States alone, greater than 20,000 organ transplantations are performed annually, and approximately 2,300 of these are heart transplants. Normally, organ transplantation is a last resort. It is performed only on patients who are in the last stages of organ failure and for whom other treatments have not been successful. Although rejection of the transplanted organ by the immune system of the recipient (immunologic rejection) is a major problem in the field of organ transplantation, an even bigger challenge is the shortage of donor organs. In 1999 in the United States, more than 55,000 individuals were awaiting...