Collecting Peripheral Blood Stem Cells
Increasingly, peripheral blood stem cells (PBSCs) are being collected for use in all types of transplants instead of bone marrow. This practice is generally more common in autologous transplants. PBSCs are harvested through a relatively simple procedure called apheresis, which is like a blood transfusion. The donor’s blood, including circulating stem cells, is collected from a large vein in the arm or through a temporary central venous line, depending on the hospital’s procedures and the donor’s physical condition.
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The blood is then run through a machine called a blood cell separator, which distinguishes the small fraction of stem cells in the blood from all other blood cells. The stem cells are collected and the rest of the cells are returned to the donor. Depending on the type of transplant and the timing of donation, the stem cells may be taken directly to the recipient for infusion or they may be treated and frozen for later use in the same method as bone marrow. Apheresis takes longer than bone marrow harvesting because there are fewer stem cells circulating in the bloodstream than there are in bone marrow. The procedure may be done either as an inpatient, which requires admission to the hospital, or as an outpatient. It usually takes two to four hours and may be repeated on several days.
A number of strategies are being explored to help “mobilize” stem cells – to induce them to leave the bone marrow and enter the bloodstream – in order to make apheresis more efficient. One method that is being increasingly used is pre-treatment with growth factors, which stimulate the production of blood cells. Two of the most-studied growth factors, colony-stimulating factors and interleukins, have been shown to increase the volume of stem cells in the blood. Patients may want to ask the doctors at the hospital about their use of growth factors for donors if considering a PBSC transplant.
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