Hematopoietic Stem Cell Transplantation
Stem cells are immature cells of body that act as "master cells" from which other vital cells originate. Stem cells can make identical copies of themselves. This keeps a constant supply of cells ready to mature into several distinct layers-internal-external medium or tissue in response to the needs of body. Stem cells mature within these layers, replacing damaged or aging cells in their respective tissues of body. Once stem cells mature, they lose the ability to duplicate themselves. Hematopoietic stem cells (stem cells of the blood) reside primarily in the bone marrow, the spongy inner portion of our bones. These master cells replenish 3 types of blood cells namely red cells also known as red blood cells, platelets, known as blood clotting cells and white blood cells or leukocytes of the immune system. When our body needs to replace damaged red blood cells, platelets for blood clotting, or immune cells, stem cells located in the bone marrow mature in a process known as hematopoiesis. Though hematopoiesis or development of blood cells continues to occur constantly in our body, but certain conditions require an increased activity of this constant development. For example, when a person tries to recover from serious bleeding or moves to a place of high altitude, increased number of stem cells should be mobilized in the bone marrow to release into the bloodstream.
On the other hand, white blood cells or immune cells leave the bone marrow when they are still immature and migrate through the bloodstream on their way to thymus gland and other lymphoid organs. During this journey, these cells get mature and become specialized B or T cells of the immune system, which are capable of killing parasites, bacteria, viral infection, and also some tumor cells. Other components of blood like RBCs or red blood cells then fully mature in the bone marrow before being released into the bloodstream.
At any given time, there is a hematopoietic stem cell circulating in the blood system of a person for every 100 present in the bone marrow. Although, it is not understood precisely how our body makes more signs asking that hematopoietic stem cells be mobilized out of the bone marrow, stem cell scientists are studying some factors that appear to increase the rate of their release.
Patients suffering from blood cancers such as leukemia, lymphoma, or myeloma undergo radiation therapy and chemotherapy, which not only destroys cancer cells but also destroys healthy bone marrow and healthy hematopoietic stem cells. Whether the cancer begins from the bone marrow itself or in the lymphoid organs, the above treatments reduce most of the body reserve of blood-forming stem cells. Even patients who do not have noncancerous diseases of blood and have other life-threatening immune disorders or anemia can develop an extreme shortage of hematopoietic stem cells. In all these types of critical conditions, hematopoietic stem cell transplantations can restore normal hematopoiesis.
Moreover, hematopoietic stem cell transplantation or blood stem cell transplants are also known as transplants of peripheral blood stem cells or bone marrow transplants depending on the location of collection site of stem cells.