After scraping a knee or donating blood, the body replenishes the blood cells that are lost by drawing on a small number of semi-specialized hematopoietic (heem-AT-oh-poh-EH-tik) stem cells contained in the blood and bone marrow. For decades, scientists have been using this type of adult stem cell to treat patients
with diseases such as leukemia, sickle cell anemia, bone marrow damage, and some metabolic disorders and immunodeficiencies where the body has lost its ability to replenish its own set of healthy blood cells. Hematopoietic stem cells give rise to all the blood cell types, from infection-fighting white blood cells to blood-clotting platelets. Preliminary results have sug- gested that they may also be able to produce other cell types not found in blood, but this is not yet proven. In the past, the only way to use hematopoietic stem cells for therapies was through bone marrow trans- plants.
Extracting bone marrow is an uncomfortable and invasive procedure, and in order for a transplant to work, the donor and recipient must be genetically similar.
If they are too genetically different, the blood cells produced from the transplanted marrow may recognize the patient’s body as foreign and fight against the patient’s own cells and organs. Additionally, the patient’s immune system may reject the transplant, causing a dangerous “war” within the patient’s body.
More recently, scientists have developed ways to derive hematopoietic stem cells from the blood contained. in the umbilical cord and placenta at birth. The stem cells isolated from a person’s own umbili- cal cord blood and placenta, if used for therapies later in life, would be less likely to cause an “inter- nal war” within the recipient’s body. They are also more accessible than the stem cells in bone marrow because the extraction of this blood poses no risk to the mother or infant.
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