An organ transplant is the transplantation of an organ (or part of one) from one body to another, for the purpose of replacing the recipient's damaged or failing organ with a working one from the donor. Organ donors can be living, or cadaveric (dead). Immunosuppressive drug are variety of substances used to prevent production of antibodies. They are clinically used to prevent rejection by a recipient's body of an organ (e.g. bone marrow, heart, kidney, liver) transplanted from a donor. A transplant is rejected when the recipient's immune system acts against it.