Three methods exist for stem cell harvesting, including harvesting stem cells from bone marrow, blood, and embryos. The peripheral blood stem cell harvesting method is preferred because it is deemed safer and requires no anesthesia for the donor or patient. Embryonic stem cell harvesting, which destroys an embryo to extract stem cells, is rife with controversy on moral and ethical grounds. Bone marrow stem cell harvesting represents an older method still used when insufficient stem cells are available via blood.
Peripheral blood harvesting might be autologous, meaning from the patient, or allogenic, from an outside donor. Two intravenous devices are placed in each arm, with one drawing blood from the body and the other returning it. A machine separates stem cells from the blood before it is returned to the donor.
Before this method of stem cell harvesting begins, the donor receives a drug that promotes white cell formation in bone marrow. Normally, there are very few stem cells available for harvesting in the blood. These drugs force bone marrow to produce massive numbers of white blood cells. The bone marrow cannot hold all these cells, so they are released into the blood, where they can be harvested. Stem cell transplants require millions of these cells to work effectively.
Timing is important in this type of harvesting to capture cells at the moment they mature into white blood cells. Drugs used in the procedure cause cells to mature rapidly into other forms unsuitable for harvesting. Donors are typically tested frequently to gauge the best time for harvesting.
A human embryo grows until hundreds of stem cells form. When these stem cells are harvested, the embryo dies. Research using animals discovered ways to remove one cell from an eight-cell embryo, which was manipulated by contact with other embryonic stem cells and grew its own stem cells. The remaining seven-cell embryo was implanted in a rat’s womb and produced normal offspring. Scientists hope to address the controversy in this area of stem cell extraction by preserving the original embryo.
When stem cell harvesting is allogenic, the patient is typically receiving chemotherapy to treat cancer. These chemicals force his or her bone marrow to react by producing white blood cells to fight foreign substances. Drugs were developed to cause the same reaction in healthy donors who are not receiving chemotherapy, and these drugs are typically given to cancer patients to enhance the production of stem cells in their bone marrow.
Bone marrow harvesting requires anesthesia before cells are extracted. Large bones typically provide the best source of stem cells, with the pelvic bone a preferred site for some doctors. This method of stem cell harvesting represents a more complex operation and usually results in more pain. It is used when sufficient stem cells cannot be extracted through the blood.
Peripheral blood stem cell harvesting can be repeated until enough cells become available. The patient might experience bone pain as the marrow works to produce more blood and white blood cells. Typically, over-the-counter pain medication controls discomfort from the procedure. Recovery is commonly quick, with no lasting side effects.