Preparation of Campath 1 monoclonal antibodies prior to mixing with donor bone marrow obtained for transplant into a woman with acute lymphoblastic leukaemia. Risk factors in bone marrow transplants are unique, because they involve the transplant of the immune system itself. In other cases the major problem would be that the recipient might reject the donated tissue; here the risk is more that the transplant would reject the recipient. To help overcome this, the monoclonal antibodies are used to purge the donor marrow of most of its T-lymphocytes - white cells responsible for instigating the attack on non-histocompatible tissue.