A transplant is an organ, tissue, or a group of cells removed from one person (the donor) and surgically transplanted into another person (the recipient or host) or moved from one site to another site in the same person. Transplantation is a complex area of medicine because when organs or tissues are transplanted from one person to another, the recipient’s immune system can reject and destroy the donor organ or tissue, and medication is needed to suppress this immune response. The treatments used vary depending on the tissue or organ being transplanted, the level of compatibility between the donor and the recipient, and other factors.