In transfusion medicine the scientific fundamentals of immunology have had a considerable clinical impact. Transfusion may suppress the immunity but some patients could suffer disadvantages including GvHD, alloimmunisation and possible cancer, where white cells (WBC) play pivotal roles in this phenomenon, presenting antigens and producing cytokines. A clinical application of this practice is LAK-cells targeted against cancer. MHC on the WBC may provide additional immunological modulations through series of secondary messengers. Thus reduction of WBC in the blood and bone marrow may be...