Hematopoietic stem cell transplantation (HSCT) is currently a standard-of-care procedure for many disorders. Frequently, HSCT procedures are curative in situations where no other curative treatment options exist. Specifically, the key element in HSCT as a therapy is the replacement of the host (recipient) marrow function by another source of hematopoietic stem cells (HSC). These sources could include HSC collected from the patient (autologous) or from another individual (allogeneic) . Allogeneic sources include family-related or unrelated products, collected either directly from healthy donors or cryopreserved stem cell products, including umbilical cord blood. A few rare patients have a syngeneic (identical twin) donor. In the setting of allogeneic HSCT, products are preferentially matched at major histocompatibility complex (MHC) human leukocyte antigen (HLA) class I and II molecules located on chromosome 6, which guide immunologic recognition as self or nonself. Advances in immunogenetics and immunobiology, conditioning regimens , disease characterization and risk stratification, immune suppression, antimicrobials, and other types of supportive care have all contributed to improvements in disease control and overall survival. These outcomes have resulted in a marked increase in the number of procedures performed annually worldwide. However, it is critical to always recognize that HSCT requires substantial resources. Thus delivering this therapy requires large multidisciplinary teams of nursing, pharmacists, physicians, social workers, nurse practitioners, physician assistants, nutrition experts, and occupational and physical therapists, in addition to specialized facility and technical resources.

HSCT has been developed over the past 50–60 years since the first human clinical experimental transplants were performed in the 1950s. One of the earliest curative allogeneic bone marrow HSCT procedures transplant was performed in a young child with immune deficiency syndrome in 1968. By the early 1980s, bone marrow transplantation was no longer considered experimental but as the standard of care for a variety of disorders including acute and chronic leukemia , aplastic anemia, lymphoma, multiple myeloma, and a number of inherited disorders including severe combined immune deficiency, thalassemia, and other inborn errors of metabolism. With this recognition, the utilization of this procedure rapidly increased to the current state where over 50,000 procedures are performed worldwide each year as estimated by the Center for International Blood and Marrow Transplant Research (CIBMTR).