Harvesting blood stem cells for transplantation
Blood stem cells used to be taken mainly from bone marrow, where they develop. Nowadays it is also possible to filter stem cells directly out of the bloodstream. The first method is called a bone marrow transplant, and the second method is called a peripheral blood stem cell transplant.
The donor’s body replaces the donated bone marrow or blood stem cells on its own within a few days. Some people feel tired during this time. It is very rare for donors to experience serious complications after donating stem cells, but temporary minor side effects are possible.
Taking stem cells from bone marrow
In order to take stem cells from bone marrow, between 0.5 and 1.5 liters of bone marrow are removed from the back of the pelvic bone (the iliac crest) using a special needle. The exact amount is determined by the concentration of stem cells in the bone marrow that is taken. To do this, the needle usually has to be inserted at different points on the bone. The stem cells are then removed from the bone marrow in a laboratory and prepared for transplantation.
Removing bone marrow is a complex procedure. The donor is given a general anesthetic, and usually spends one to two days in the hospital. In the first few weeks following the procedure, there may be bruising and pain where the needle was inserted. Some people mainly have temporary back pain. Having an anesthetic is always associated with certain risks too. And there is a risk of infection from the surgical procedure. For these reasons, stem cells are generally taken from blood nowadays.
Removing stem cells from blood
Using peripheral stem cells has the advantage that no anesthetic is needed and you do not have to stay in the hospital. The blood usually only contains very few stem cells, so four to five days before the procedure is carried out a drug is injected under the skin (subcutaneously) once or twice. This drug is a growth factor known as GCSF (granulocyte colony-stimulating factor). It stimulates the movement of more blood stem cells from the bone marrow into the bloodstream.
After a few days, when there are enough stem cells in the blood, the blood is taken from a vein in one arm and passed along a tube into a special centrifuge called an apheresis machine. Here the stem cells are separated from the blood (a process known as apheresis). The blood is then returned to the body through another tube that goes into a vein in the other arm. Apheresis takes about two to three hours. The procedure of removing blood stem cells is usually carried out in an outpatient setting. In order to obtain enough blood stem cells, though, it often needs to be repeated once or twice in the days following the initial procedure.
The advantage of harvesting the stem cells from blood instead of from bone marrow is that it doesn’t require the use of a general anesthetic.
But there may still be side effects. The growth factor drug may cause temporary problems such as joint pain, headaches or bone pain.
Umbilical cord blood
Another possible source of stem cells is umbilical cord blood and blood taken from the child’s part of the placenta. With the parents’ consent, this blood can be donated anonymously to a public umbilical cord blood bank. There are also private umbilical cord blood banks that can be paid to store a child’s umbilical cord blood for the child’s own use. Based on current scientific knowledge, however, it is highly unlikely that the newborn child will benefit from the blood later in life. The most common cancers that affect children and teenagers, such as leukemia, can’t be treated using their own stem cells. This is because the stem cells that were taken at birth may already have included cancer cells, which would then be transferred back into the body.
Stem cells harvested from umbilical cord blood are currently only transplanted to other people.
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