Engraftment is a term used when discussing stem cell transplantation. It refers to a state in which the body of the stem cell transplant recipient accepts the donated or stored stem cells.
During stem cell transplantation, the bone marrow of the recipient is damaged by chemotherapy with or without radiation therapy to the point where it can no longer function. It is rendered unable to produce healthy red blood cells, platelets or white blood cells. In fact, the damage is so severe that the patient will die unless their marrow function is restored by an infusion of stem cells, either from a donor, or the patient's own cells that were previously collected and stored.
Once the donated stem cells are infused into the recipient, they find their way into the marrow space in the bones. When they are in place and begin to reproduce, engraftment occurs. The stem cells will create a new hematopoietic and immune system for the recipient.
A slow and steady increase in blood cell counts indicates that engraftment is occurring. Early on in the process, complete blood cell count will show a rise in white blood cells and a shift from predominantly lymphocytes to neutrophils.
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Cutler, C. “Bone Marrow Transplantation” in Stern, T., Sekeres, M. eds (2204) Facing Cancer. McGraw-Hill: New York.