BONE MARROW TRANSPLANTS
The most widely used and successful stem cell therapy is bone marrow transplants. Stem cell transplants can replace diseased bone marrow with hematopoietic stem cells that can later develop into healthy bone marrow. This treatment can help patients suffering from multiple kinds of cancer, including leukemia, multiple myeloma, and certain types of lymphoma. Chemotherapy uses radiation to destroy the cancerous cells, but then they must be replaced with transplanted stem cells. Blood marrow transplants can treat severe blood diseases as well, such as thalassemias and anemias (aplastic and sickle cell). These diseases all involve the loss or scarcity of different kinds of blood cells, so stem cell transplants are able to provide the cells that the patients need. Hematopoietic stem cells can differentiate into nearly any kind of blood cell, including white blood cells, red blood cells and leukocytes, so they can treat many types of blood diseases and cancers.
There are two main types of stem cell transplantation: autologous and allogenic. Autologous transplantation is when a patient's own stem cells are used to replace his/her damaged blood cells. It works best when the patient still has enough healthy blood stem cells. The collected cells are frozen and stored for later treatments. Allogenic transplantation is when a patient uses a donor's stem cells. The donor may be a relative or an unrelated person, but the bone marrow should match the patient's as closely as possible. Scientists use HLA (Human Leukocyte Antigen) tissue typing to identify the different combinations of protein present on the surface of blood cells. Near perfect HLA-matched bone marrow reduces the risk of rejection and graft-vs-host disease, where the newly transplanted cells attack the patient's foreign tissues.
The hematopoietic stem cells come from cord blood, peripheral or bone marrow stem cells. Umbilical cord blood contains many blood stem cells that are less prone to rejection. Peripheral stem cells are found in the bloodstream, which makes them easier than bone marrow stem cells, but they are sparse so it is difficult to collect enough for a successful transplant. Bone marrow stem cells must be extracted from the bone (usually the pelvis) with a hollow needle.
