Bone marrow produces more than 20 billion new blood cells every day throughout a persons life. The driving force behind this process is the hematopoietic stem cell. Hematopoietic stem cells are immature cells found in both the bloodstream and bone marrow. These specialized cells have the ability to create more blood-forming cells or to mature into one of the three different cell types that make up our blood. These include red blood cells (cells that carry oxygen to all parts of the body), white blood cells (cells that help the body fight infections and diseases), and platelets (cells that help blood clot and control bleeding). Signals passing from the body to the bone marrow tell the stem cells which cell types are needed the most.
Types of stem cell transplantation
There are two main types of stem cell transplantation:
Autologous transplantation (AUTO). A patient undergoing an AUTO transplant receives his or her own stem cells. During the AUTO transplant process, the patients stem cells are collected and then stored in a special freezer that can preserve them for decades. Usually the patient is treated the following week with powerful doses of chemotherapy and/or radiation therapy, after which the frozen stem cells are thawed and infused into the patients vein. The stem cells typically remain in the bloodstream for about 24 hours until they find their way to the marrow space, where they grow and multiply, beginning the healing process.
Allogeneic transplantation (ALLO). A patient undergoing an ALLO transplant receives stem cells donated by another person. As a result, the first step for an ALLO transplant is to find a donor match. Specific proteins, called human leukocyte antigens (HLA), are found on the surface of white blood cells and throughout the body. The combination of these proteins makes each persons tissue unique. HLA typing is a special blood test that identifies these proteins. A successful bone marrow transplant requires the donation of near-perfect HLA-matched bone marrow. HLA-matched blood stem cells given to a person during transplantation are less likely to result in graft-versus-host disease (GVHD, a complication in which the immune cells in the transplanted bone marrow recognize the recipients body as foreign and attack it). Siblings (brothers or sisters) usually have the best chance of being a complete match. Occasionally, other family members can be a match. In some cases, an unrelated volunteer donor may be the best match. Learn more about donating bone marrow.
Once a donor has been identified, stem cell donation is coordinated so it occurs as close to the end of the patients initial chemotherapy and/or radiation therapy as possible. On the day of the transplant, the patient receives the unfrozen donated stem cells through an IV that delivers them into his or her vein.