| Definition |
This is a technique that was developed to restore the marrow of patients who had lethal injury to that site. Such injury can occur because of primary marrow failure, destruction of marrow by disease, orintensive chemical or radiation exposure. As first designed, the source of the transplant was the marrow cells of a healthy donor who had the same tissue (HLA)type as the patient. Usually, the source was a brother or sister. Donor programs have been established to identify unrelated donors who have a matching tissuetype. This approach requires screening tens of thousands of unrelated individuals of similar ethnicity. The transplant product is a very small fraction of the marrow cells called “stem cells.” These stem cells not only reside in the marrow but also circulate in the blood. They can be harvested from the blood of a donor by treating the donor with an agent or agents that cause are lease of larger numbers of stem cells into the blood and collecting them by hemapheresis. The stem cells circulate in large numbers infetal blood also, and can be recovered from the placental and umbilical cordblood after childbirth. The harvesting, freezing and storing of “cord blood” hasprovided another source of stem cells for transplantation. Since blood as wellas marrow is a very good source of cells for transplantation, the term “stem cell transplantation” has replaced “bone marrowtransplantation” as the general term for these procedures. If the donoris an identical twin, the transplant is called “syngeneic,” the medical term for genetically identical. Ifthe donor is a non-identical sibling, the transplant is called “allogeneic,” indicating it is from the same species and inpractice nearly always matching in tissue type. The term “matched-unrelated” is applied to the donor recruited from large volume screening programs searching for the rare individual who is very similar in tissue type to the patient. The important technique of harvesting a patient´s marrow, freezing it and returning it to them after they have received intensive chemotherapy and or radiotherapy for their underlying disease has been referred to as autologous (self) or auto-transplantation. This term is a well-entrenched misnomer since transplantation implies transferring tissue from one individual to another. This technique would better be referred to as autologous marrow infusion.
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