The correct option is A rejection of graft by body’s immune system
Graft is any tissue or organ that is surgically transferred from donor to recipient. Patients suffering from permanent kidney failure can receive a kidney from a suitable donor. But individuals whose kidney matches with that of recipients can only donate a kidney. If the donor kidney does not match then the recipient’s immune system considers the graft as foreign and attacks it. This process is called graft rejection.
Hence, graft rejection is rejection of graft by the body's immune system.