The body is able to differentiate ‘self ’ and ‘non -self’.  Which of the following is responsible for graft rejection ?

Tissue matching, blood group matching are essential before undertaking any graft/transplant and even after this the patient has to take immuno–suppresants all his/her life. The body is able to differentiate ‘self ’ and ‘nonself’ and the cell-mediated immune response is responsible for the graft rejection