Answer: Rejection by transplant recipient's immune system of the transplanted organ is one of the major cause of transplant failure.
Explanation: Our body's immune system act as a defense system to defend our body from any disease or infection. Immune system kills the foreign body that enters into our body to make us sick. When an organ transplantation occurs sometimes the body's immune system considers the newly transplanted organ as a foreign body and started eating it, thus causing the transplant to fail.