Haematopoietic stem cell transplantation (HSCT) involves a patient receiving stem cells to help the bone marrow produce healthy blood cells. Stem cells are unspecialised cells that can develop to become different types of specialised cells. HSCT is used to treat serious diseases of the blood and immune system. A stem cell transplant in which the patient receives cells from a matched donor is called an allogeneic transplant. Before receiving the transplant, treatment is given to clear cells from the patient’s own bone marrow. The patient then receives the donor cells, which multiply and develop into healthy specialised blood and immune cells.