What is bone marrow transplantation ( BMT )
BMT means transplanting one’s own diseased bone marrow with healthy bone marrow. Your bone marrow is destroyed using radiation or/ and cytotoxic drugs first, then healthy bone marrow/ umbilical cord blood is transfused. This procedure results in regeneration of healthy marrow, which cures the disease.
Since bone marrow is responsible for the production of all white cells, red cells and platelets, BMT is used for treating leukemia (blood cancer) and some forms of anemia.
Benefits and limitations of BMT
To understand this, it is necessary to know some basic hematology. The bone marrow is the only tissue in the adults which produces all cellular components. In the adult humans it is distributed in several parts of the body viz. skull, sternum and pelvic girdle (iliac crest). This tissue continuously produces the red cells and white cells which are lost regularly, for the entire life of the individual. This is possible due to the presence of a small number of “Stem cells “. The stem cells are located in the “ niches, present only in the bone marrow, which have the unique property of “ self renewal “, which makes it possible to maintain their population, while contributing cells for differentiation to blood cells all through the life of the individual. During the transplantation process the stem cells travel through the blood stream and by a very complicated process reach the bone marrow stem cell niche, where they establish themselves and start dividing. One of the two daughter cells remain as stem cells and the other undergoes division and differentiation to give rise to mature functional blood cells.
Leukemias are caused due to mutations in the stem cell population and therefore, the only effective way to treat blood cancers is by bone marrow transplantation. Similarly, some anemias like fanconi’s and thalasseamias are due to stem cell defects and the only effective way to treat these diseases is by transplanting with normal donor bone marrow.
Though BMT is a very effective, it has some limitations. The most important being HLA(Human leukocyte antigen) compatibility. All the cells in the body display these markers on the cell surface which determines “Self and Non self”. No two individuals except identical twins have the same HLA markers. In the general population, it is like finding a needle in the hay stack. When a mismatched graft is transplanted into a host, rejection takes place and results in “ Graft versus Host disease”, a severe life threatening reaction.
The number of bone marrow cells transplanted is always very high because the process of stem cell homing into the host marrow niches is random. Most of the cells are lost in the lung and liver never reaching the bone marrow. This puts a severe restriction on the size of the donor sample.
The process of transplantation involves destruction of the marrow cells by radiation and chemotherapy which results in severe neutropenia and immuno suppression which may lead to life threatening complications. These patients need to be kept in sterile living conditions, which results in huge expenses.
Can Umbilical cord blood stem cells substitute for donor marrow
Umbilical cord blood is the residual blood present in cord after the baby is delivered. This has been known to contain stem cells similar to the marrow.
These stem cells are superior to the bone marrow derived by virtue of their multipotence and reduced expression of HLA markers, making them less prone to rejection in spite of HLA mismatch. Several national and international studies have shown that successful regeneration of marrow takes place when umbilical cord blood is used for transplantation.
Another major advantage is that, the cord blood can be collected at the time of birth and cryo preserved in bank. The stem cells can be HLA characterized and a registry can be made. Whenever a stem cell is needed for transplantation, appropriate sample can be thawed out and used for transplantation. This greatly improves the chances of finding an appropriate stem sample for transplantation. These are the public cord blood banks. However, unfortunately, another form of banking cord blood has become more prevalent especially, in India viz. the autologus cord banking also known as private cord blood banks. These banks cryopreserve umbilical cord blood of your child for your own child’s use, at any time in the future, for a fee. Though, this type of banking has limited use as a source of stem cells since it cannot be used for transplantation in case your child develops any of the stem cell derived diseases.
Autologus bone marrow transplantation
Autologous bone marrow transplant means using the bone marrow of the same person for transplantation. This is possible when the person’s bone marrow is healthy. This procedure is used in the treatment of solid tumors which do not affect the bone marrow. This is actually a rescue procedure. One of the major limitations of chemotherapy is that it kills normal cells along with the cancer cells. The given dose is so adjusted that the cytotoxic drug does not kill the normal cells. One of main tissue which is affected is bone marrow, resulting in anemia and nutropenia, which may become life threatening. Therefore, it has to be protected, if the dose of the cytotoxic drug has to be increased, which is often needed since cancer cells can become resistant to the drugs. One of the ways by which this is done is by mobilizing the stem cells from the marrow by injecting the patient with a growth factor called Granulocyte colony stimulating factor(GCSF) and collecting into a sterile bag which will be cryopreserved. After the increased dose of drug is given the stem cells are re-infused.
What is Stem cell transplantation
The bone marrow contains stem cells which give rise to blood cells normally; but can also result in other tissue cells. This property makes them useful in regenerative medicine.
Another type of stem cell which is found in bone marrow, is the Mesenchymal stem cells. These cells have been shown to be important in regenerative medicine.