Stem cell transplantation is a generic term covering several different techniques (see fig 1). Allogeneic transplants are haemopoietic stem cells from the bone marrow, peripheral blood, or umbilical cord blood of a healthy donor matched for HLA type, who may be a family member or an unrelated volunteer. Autologous transplants are stem cells from the patient's own bone marrow or peripheral blood.

Allogeneic transplantation was first used to treat congenital immune deficiencies, bone marrow failure, and haematological malignancies and is now used routinely for some non-malignant conditions such as thalassaemia. Autologous transplantation was introduced to rescue the bone marrow of patients due to undergo high dose chemotherapy, and it is now increasingly written into protocols for the primary treatment of solid tumours such as breast cancer and neuroblastoma. Autologous transplantation is also used experimentally to treat difficult autoimmune conditions such as systemic sclerosis and as a vehicle for gene therapy. Knowledge of stem cell transplantation techniques and their clinical application is therefore becoming essential for increasing numbers of medical specialists.