In this section we will provide answers to some of the commonly asked questions about blood and marrow transplants, including:
- What is a blood stem cell/bone marrow transplant?
- What is bone marrow? What are stem cells?
- How are stem cells and bone marrow collected for transplant?
- How are stem cells used for transplant?
- What evidence is there of transplantation success?
What is a blood stem cell/bone marrow transplant?
The object of blood stem cell or bone marrow transplantation is to rid the body of cancerous cells and replace them with healthy blood cells. There are many different types of transplant procedures, each of which has different complications and risks and is more appropriate for specific diseases. The choice of type of transplant can be complicated and needs to be discussed in detail with your doctor.
The cells that are ultimately transplanted are known as "hematopoietic stem cells." This means that these cells are capable of producing all of the cells that circulate in the blood (red cells that carry oxygen, white cells that fight infection, platelets that help control bleeding), along with all the cells of the immune system.
Hematopoietic stem cells can be obtained from yourself (autologous transplantation) or someone else (allogeneic transplantation). If obtained from someone else, they can be a relative (matched related allogeneic transplantation) or a volunteer donor from the national marrow donor program (matched unrelated donor allogeneic transplantation) or from a donated umbilical cord blood (unrelated cord blood transplantation). Often we obtain hematopoietic stem cells from the bone marrow (bone marrow is the spongy tissue found in the core of bones. Its main purpose is to produce stem cells - the primary cells in the marrow), in which case the procedure is termed bone marrow transplantation. More frequently, we now obtain hematopoietic stem cells from the blood, in which case the procedure is known as mobilized peripheral blood stem cell transplantation, or stem cell transplant for short.
The risks, benefits and underlying theories for each of these transplants varies from one disease to the next and should be discussed in detail with the transplant specialist involved in your case.
What is bone marrow? What are stem cells?
Bone marrow is a spongy tissue found inside bones. Its main purpose is to produce stem cells, which are the most primitive cells in the marrow.
Stem cells make the body's three main types of blood cells: white blood cells (WBCs), red blood cells (RBCs) and platelets:
- White blood cells fight infection by killing bacteria and viruses. When there are too few white blood cells in the body, the patient has a harder time fighting infection.
- Red blood cells carry oxygen from the lungs to the body's cells. The body needs oxygen in its cells to process nutrients in food and remove waste products. Patients who have too few red blood cells become anemic.
- Platelets clot the blood and help stop bleeding. A low number of platelets may cause patients to bruise and bleed too easily.
How are stem cells and bone marrow collected for transplant?
Stem cells and bone marrow can be taken from the patient or from a donor. Harvesting of cells always takes place before high-dose chemotherapy and/or radiation is given. Cells may be collected in three ways:
1. Bone Marrow Harvesting
- Bone marrow is taken, usually from the pelvis bone, using a large needle or special syringe. Blood and bone fragments are removed from the marrow that is collected. Aspiration requires anesthesia and is usually done in the operating room. The procedure can be performed on an inpatient or outpatient basis. Patients may experience tenderness, mild stiffness and soreness, which can be relieved by pain medication and exercize
- There are fewer stem cells circulating in the blood than in the bone marrow. To increase the number of stem cells that can be harvested from the blood, doctors use growth factors. These substances stimulate the growth of stem cells. A catheter is inserted into a large vein, blood is drawn into a machine that removes stem cells. The rest of the blood is then returned to the patient. This process is known as apheresis or leukaphersis. The process takes approximately 5 hours and does not usually require a hospital stay.
How are stem cells used for transplant?
Stem cells may be used in different ways, depending on the type of transplant. They may be saved and frozen for later replacement in the patient's system, or they may be given to the patient almost immediately.
After cells are collected, the patient undergoes chemotherapy and/or radiation to rid the body of cancer cells. This also creates space in the bone marrow for the new cells. Chemotherapy and radiation reduce the risk of the patient rejecting cells that come from a donor.
The harvested bone marrow or blood stem cells are given to the patient using a flexible tube inserted into a vein. These cells proliferate and result in the production of normal blood cells.
What evidence is there of transplantation success?
Stem cell/bone marrow transplants are becoming more common as the procedure is continually refined. Transplantation is an effective way to combat many types of cancers. The commonest cancers for which transplantation is recommended include: multiple myeloma, leukemia, non-Hodgkins lymphoma, Hodgkin's lymphoma and testicular cancer.
Further transplant research is being conducted on the use of blood stem cell/bone marrow transplants in other conditions including amyloidosis, thalassemia and sickle cell disease.