Bone Marrow

Bone marrow transplants treat a variety of blood and bone marrow diseases (see Medical Transplantation). In a conventional transplant, a donor and recipient are matched as closely as possible for blood type. The red marrow from the donor is suctioned from the pelvic bone with a long needle attached to a syringe. The marrow sample is treated to remove the donor’s white blood cells, which otherwise would attack the recipient’s tissues. The treated marrow is then given to the recipient through an intravenous infusion, which introduces immature, but healthy, cells into the bloodstream. These cells migrate to the marrow, where they mature and eventually divide, populating the circulatory system with healthy cells. The transplanted stem cells serve as a continual source of healthy cells. While bone marrow transplants are helpful, they cannot always cure a blood or bone marrow disease because the match between donor and recipient is seldom perfect. The immune system of the recipient may attack some of the donor’s cells, which interferes with the benefits of the transplant.

Increasingly, only the stem cells from a bone marrow are used in a bone marrow transplant. Called a stem cell transplant, this procedure is often used for cancer patients who will be undergoing extensive radiation and chemotherapy treatments that will likely irreparably damage the bone marrow. Prior to undergoing radiation or chemotherapy, some of the patient’s own marrow is removed and screened to eliminate cancer cells in a technique called a stem cell wash. The population of healthy stem cells is kept alive in the laboratory. After the chemotherapy and radiation treatments, the patient’s stem cells are returned to the bloodstream. They travel to the marrow and begin the process of blood cell production. The advantage of this type of stem cell transplant—in which the patient is both donor and recipient—is that the immune system will not be activated to destroy the transplanted cells. The disadvantage is that it takes longer for functioning cells to get into the blood stream, since only stem cells, and not cells in all stages of development, are transferred.

A newer stem cell transplant technique involves injecting a patient with high doses of the growth factors that stimulate white blood cell production. This causes stem cells to be released into the blood stream. The blood is then drawn and the stem cells are harvested. This technique has the advantage of being less invasive than retrieving stem cells from bone marrow.

Other types of stem cell transplants, which require both a donor and a recipient, are used to correct genetic disorders such as sickle-cell anemia, in which red blood cells are distorted and unable to transport oxygen properly. Sometimes the source of stem cells for these transplants is blood from the umbilical cord or placenta of a newborn infant. New techniques that match the blood cell producing genes of donors and recipients rather than the blood types may offer more success in these transplants.