What is a Stem Cell Transplant?
A stem cell is the cell from which all blood cells develop. Blood cells are essential to life. The different types of blood cells are red blood cells, white blood cells and platelets.
- Red blood cells carry oxygen from the lungs to all the organs and pick up carbon dioxide which is carried to the lungs and expelled from the body when you exhale.
- White blood cells are infection fighters. There are several types of white blood cells including granulocytes (also called neutrophils, polys, segs, bands, basophils and eosinophils), monocytes and lymphocytes. They work to prevent infection, and they are necessary to fight infection if it develops.
- Platelets help the blood to clot and prevent serious bleeding when you are injured, as well as perform normal repair work in your blood vessels.
Originally, it was thought that stem cells were only found in the bone marrow. However, as scientists became more skilled at identifying different types of cells circulating in the blood, it was discovered that stem cells are also found in the blood stream or peripheral blood.
Prior to the transplant, you will receive very high-dose chemotherapy to treat your cancer. The chemotherapy will destroy cancer cells, but unfortunately the chemotherapy cannot tell the difference between cancer and healthy cells. The chemotherapy destroys many types of cells that divide and reproduce rapidly, including healthy cells that produce red blood cells, white blood cells, and platelets. Without these blood cells the risk of infections, bleeding problems, and lower amounts of oxygen in the blood (anemia) is present.
Your own stem cells or a donor's stem cells can be collected and stored before the high-dose chemotherapy is given. The stored stem cells can then be returned to you intravenously after the high-dose chemotherapy to replace the stem cells that were destroyed. This is a stem cell transplant. These stem cells may come from either the peripheral blood or bone marrow.
Sometimes the terms bone marrow transplant and peripheral stem cell transplant are interchanged. A peripheral blood stem cell transplant is done to replace the same type of cell (the stem cell) that is replaced in a bone marrow transplant. The main difference between the two terms is the method in which the stem cells are collected.
There are some reasons that the transplant physician will chose one collection method over the other that will be discussed with you.
Here are some commonly asked questions:
What are Stem Cells?
Stem cells are distinguished from other cell types by two characteristics. First, they are unspecialized cells capable of renewing themselves through cell division, sometimes after long periods of inactivity. Second, under certain physiologic or experimental conditions, they can become tissue- or organspecific cells with special functions. Blood stem cells are produced and reside primarily in marrow, the spongy interior of bones. These stem cells can divide to become more stem cells. People are constantly making stem cells from their bone marrow, and this continuous production helps to naturally replace the blood cells as they complete their life cycle.
How do Stem Cells Benefit Cancer Patients ?
In patients with blood cancers, the chemotherapy and radiation that kill malignant cells also destroys healthy marrow and its blood stem cells. Whether the cancer begins in the marrow itself or in lymphoid or other organs, cancer treatment can diminish much of the body’s reserve of blood-forming stem cells. Even patients with noncancerous blood diseases can develop a shortage of blood stem cells, as occurs in lifethreatening anemias or immune disorders. In all these cases, a blood stem cell transplant can restore normal hematopoiesis, or the development of blood cells.
What is the difference between Stem Cell and Bone Marrow Transplants?
Stem cell transplantation usually refers to cases in which the stem cells are collected from the peripheral blood by a procedure called apheresis. During apheresis, blood is removed from the person’s body and goes into the apheresis machine where it is separated into its various components, which includes stem cells. These cells are collected, and the rest of the components are returned back into the body. Bone marrow transplant refers to a transplant in which stem cells are collected from the bone marrow by procedure called bone marrow harvesting. Stem cells are collected by inserting a needle into the soft center of the bone, the marrow. Most sites used for bone marrow harvesting are located in the hip bones and the sternum. The procedure takes place in the operating room. The donor will be anesthetized during the harvest and will not feel the needle. In recovery, the donor may experience some pain or discomfort in area the where the needle was inserted.
How do I know if I am an ideal candidate for Stem Cell Transplant?
Your doctor will consider your overall health and your age. People who are good candidates usually are younger than 70, do not have other diseases such as heart disease or diabetes, and have a normal kidney and liver. Your doctor will also consider how much your disease has grown, how aggressive your cancer is, and how well it has responded to previous treatment. People with aggressive cancer that has spread to many areas of the body are not usually thought to be good candidates.
Are there different types of Stem Cell Transplants?
Yes, there are three different types of stem cell transplants: autologous transplants, allogeneic transplants and matched unrelated donors (MUD).
Autologous transplants use your own stem cells. It is safer for patients to use their own stem cells in a transplant rather than someone else’s because their body will not reject its own stem cells. But it also means that these patients are more likely to have a relapse because their own marrow or blood may still contain some of the cancer cells they are trying to get rid of. Cells from another donor may work better at attacking any leftover cancer cells still in their body.
Allogeneic transplants use related donors stem cells from a matched sibling. Many factors determine how the immune system knows the difference between ”self” and “non-self”, but the most important for transplants is the human leukocyte antigen (HLA) system. Human leukocyte antigens are proteins found on the surface of most cells. They determine a person’s tissue type. (This is different from a person’s blood type.)
How well the donor’s and recipient’s HLA tissue types match plays a large part in determining whether the transplant will be successful.The best matches are where all of the HLA antigens are the same. Because HLA antigens are inherited, the search for a donor usually starts with the patient’s brothers and sisters, if possible. The chance that any sibling would be a perfect match (that is, that you both received the same set of HLA antigens from each of your parents) is 1 out of 4.
Matched Unrelated Donors (MUD) use stem cells matched from an unrelated donor. If a good match is not found in a sibling, the search may then move on to a donor search pool of 10 million registered donors or to other relatives.