Bone marrow is the spongy tissue inside your bones where blood cells are made. The "parent cells" of all blood cells are called hematopoietic stem cells. Stem cells divide and form the different cells that make up your blood and your immune system. Stem cells make millions of blood cells every day.
The three main types of blood cells are:
Red blood cells: These cells form the "blood" we’re most familiar with. Red blood cells travel from the heart and lungs, carrying oxygen to the rest of your body. The oxygen is carried on molecules called hemoglobin. Most of your blood cells are red blood cells. A low number of red cells (or low hemoglobin) can make you tired or breathless.
White blood cells: White blood cells fight infection and, therefore, are an important part of the immune system. A low white blood cell count increases the risk of developing an infection. There are several kinds of white blood cells. Neutrophils are important white cells that help fight infections caused by bacteria and yeasts. Others, called lymphocytes, carry the immunologic memory to protect against viral and other infections, especially those for which people receive vaccinations.
Platelets: Platelets help your blood to clot when you have an injury. They are smaller than red and white blood cells. A low platelet count increases the risk of bleeding and bruising.
How BMT Works
To prepare for BMT, high doses of drugs (called chemotherapy) and sometimes radiation are given for two reasons: to destroy cancer or disease and to suppress the patient’s immune system, preventing rejection of the transplant. An intravenous infusion (transplant) of stem cells, previously donated by you or by a donor, should restore your ability to make blood cells. These stem cells plant themselves in your bone marrow, almost like seeds in the ground, and reproduce, making new bone marrow and new blood cells.
The term BMT is a bit confusing. It sounds like an operation, like an organ transplant, but it is not a surgical procedure. It’s more like a blood transfusion.You may wonder, too, what the difference is between bone marrow transplant, peripheral blood stem cell transplant, and umbilical cord blood transplant. The main difference is the source of the stem cells and how they are collected. Regardless of their source, stem cells are given to the patient in the same way: by intravenous (IV) infusion.
Transplant Cell Sources: Bone Marrow, Peripheral Blood, Umbilical Cord Blood
In a bone marrow transplant, hematopoietic stem cells are collected from your own bone marrow or from a donor’s. Bone marrow is aspirated from the pelvic bones using a special needle and syringe.
Stem cells can also be collected from blood. These stem cells are referred to as peripheral blood stem cells. They are collected, or "harvested," using a large intravenous (IV) needle or a special IV catheter called a central venous catheter. In a peripheral blood stem cell harvest, the blood circulates through a special centrifuge, which removes the white blood cells along with the stem cells and then returns the red blood cells to the body. This procedure is often referred to as apheresis or, more specifically, leukapheresis. It is done on an outpatient basis.
A third source of stem cells is blood from the umbilical cord and placenta of a newborn.This blood is a particularly rich source of stem cells, taken from what is normally discarded after a baby is delivered. Cord blood from a related or unrelated baby donor may be used for transplant. Some hospitals collect cord blood (with parental consent) for donation to cord blood banks.
The term BMT is used for any transplant involving stem cells, regardless of their source.
Transplant Types: Allogeneic and Autologous
In an allogeneic BMT (sometimes called allo transplant), stem cells come from a donor. The donor may be a relative, usually a brother or sister, or an unrelated donor. Unrelated donor transplants are sometimes referred to as URD or MUD (matched unrelated donor) transplants.
To find a suitable donor, you’ll have your blood tested and typed so that it can be compared to blood samples of potential donors. This typing, called HLA typing, is a way to find a donor who is a good match for you so that your body won’t reject the transplanted stem cells.
An autologous BMT (sometimes called auto transplant) uses stem cells taken from your own body. Drugs called growth factors, which encourage the growth of stem cells, are given prior to harvesting the stem cells. Stem cells are then collected from your blood or bone marrow and are processed, frozen, and stored. After your treatment with chemotherapy and/or radiation, the harvested cells are thawed and transfused back into your bloodstream through the central venous catheter.
