Hematopoietic stem cell transplantation (HSCT) is the transplantation of multipotent hematopoietic stem cells, usually derived from bone marrow, peripheral blood, or umbilical cord blood. It may be autologous (the patient's own stem cells are used) or allogeneic (the stem cells come from a donor). It is a medical procedure in the field of hematology, most often performed for patients with certain cancers of the blood or bone marrow, and hematologically-based autoimmune disorders. In these cases, the recipient's immune system is either completely eliminated (Myeloablative) or partially eliminated (Non-myeloablative) with chemotherapy before the transplantation. Graft-versus-host disease are major complications of allogeneic HSCT. Infection is a major complication for both allogeneic and autologous HSCT.
The chemotherapy given immediately prior to a transplant is regimen, the purpose of which is to help eradicate the patient's disease prior to the infusion of HSC and to suppress immune reactions. The bone marrow can be ablated (destroyed) with dose-levels that cause minimal injury to other tissues. In allogeneic transplants a combination of cyclophosphamide with total body irradiation is conventionally employed. This treatment also has an immunosuppressive effect that prevents rejection of the HSC by the recipient's immune system. The post-transplant prognosis often includes acute and chronic graft-versus-host disease that may be life- threatening. However, in certain leukemias this can coincide with protection against cancer relapse owing to the graft versus tumor effect. Autologous transplants may also use similar conditioning regimens, but many other chemotherapy combinations can be used depending on the type of disease.
Non-myeloablative HSCT, also termed reduced-intensity conditioning (RIC), uses doses of chemotherapy too low to eradicate all the bone marrow cells of the recipient. Instead, non-myeloablative transplants run lower risks of serious infections and transplant-related mortality. Also significantly, while requiring high doses of immunosuppressive agents in the early stages of treatment, these doses are less than for conventional transplants.
Because of their gentler conditioning regimens, these transplants are associated with a lower risk of transplant-related mortality. The optimal procedural strategy for each disease and recipient is highly individualized.