Damage and scarring of a transplanted kidney has become the most common cause of loss of the transplanted kidney. This kidney damage is a complex process caused by many factors including injury during obtaining and transplanting the kidney, injury from the immune system, injury from infections, and injury from drugs used to stop rejection. This injury leads to scars that decrease the kidney's ability to function properly, and over time the kidney is lost. Prograf® (tacrolimus) has been one of the main drugs used to prevent rejection. However, when used over time it has been shown to cause chronic damage and scarring in the transplanted kidney.