Befo­re a stem cell trans­plan­ta­ti­on, the patient’s bone mar­row is des­troy­ed with che­mo­the­ra­py, often in com­bi­na­ti­on with irra­dia­ti­on. The pur­po­se is on the one hand to eli­mi­na­te as many of the mali­gnant cells in the patient’s body as pos­si­ble, and on the other hand to ensu­re that the cells trans­fer­red from the donor can grow and are not outn­um­be­red by the patient’s cells and the­re­fo­re rejected.