Also known as a BMT, stem cell transplant, or hematopoietic stem cell transplant
Bone marrow is found in the center of bones and is where blood cells are made. It is found in the spongy part of the bones, especially the hips, ribs, breastbone, and spine. Bone marrow contains the youngest type of blood cells known as hematopoietic stem cells. As a hematopoietic stemcell ages, it becomes a white cell, red cell, or platelet. Hematopoietic stem cells are found in bone marrow, peripheral blood (bloodstream), and umbilical cord blood.
A bone marrow transplant (BMT) replaces diseased or damaged cells with non-cancerous stem cells that can grow healthy, new cells. BMT is usually used when cancer treatments have destroyed normal stem cells in the bone marrow. The stem cells can be replaced through BMT. A BMT is also performed when the chances for cure with chemotherapy alone are low.
Types of Bone Marrow Transplant (BMT)
There are two major types of BMT, and the type that your child will receive depends upon the diagnosis.
- Allogeneic: An allogeneic transplant is performed when bone marrow or blood cells are received from a donor other than the patient. These can come from a related donor, unrelated donor, or cord blood. This type of transplant is used for patients with leukemias and some lymphomas.
- Autologous: An autologous transplant is performed when the patient’s own bone marrow or blood cells are used. The marrow or cells are collected and frozen, and then thawed when needed for reinfusion. This type of transplant is used for patients with solid tumors such as neuroblastoma, Hodgkin disease, and brain tumors.
Obtaining Bone Marrow Cells
The first step is to locate a donor whose blood cells closely match the patient’s. This is done by tissue typing prospective donors. Tissue typing is done by a blood sample and is called HLA typing, which stands for Human Lymphocyte Antigens. These antigens are found on the surface of white blood cells. A patient’s full siblings each have a 25% chance of being a tissue type match. Less commonly, a parent may match the patient. Occasionally, a less- than-perfectly matched related donor is used.
If a related donor is not available, then a search for a compatible, unrelated donor is performed through the National Marrow Donor Program. Unrelated donor cells can come from a living donor or frozen cord blood. Your physician will decide what the best source for donor cells is for your child. This is based upon urgency of the transplant, weight of your child, and the best tissue type match. An unrelated donor search may take several months; cord blood can be obtained within a few weeks.
Peripheral stem cells are usually collected for autologous transplant, but stem cells from the bone marrow also can be used. These are collected either before the patient has chemotherapy or following a course of chemotherapy. To collect peripheral stem cells, the patient receives medications (such as G-CSF and/or GM-CSF) to increase the number of peripheral blood stem cells available.
Cells are collected through a process called apheresis. An apheresis machine has a circuit that will collect blood, separate, and remove white blood cells containing stem cells, and then return red blood cells to the patient. This process takes about 4 hours and may need to be repeated for 2 or 3 days in a row. For certain diseases, the peripheral blood stem cells may be treated with anticancer medications to prevent tumor cells from being placed into back into the patient’s body.