Bone Marrow Transplantation
What is Bone Marrow Transplantation?
Bone marrow transplantation (BMT) is a medical procedure in which some or all of a patient's own bone marrow is destroyed, and new bone marrow is infused into the patient's blood stream. In a successful transplant, the new bone marrow moves into the cavities of the large bones, engrafts and begins producing normal blood cells.
- Standard BMT and its Limitations
Standard bone marrow transplants (BMTs) have been performed for over 55 years for treatment of anemia and leukemia. Due to various medical advancements, BMTs can now be used to treat other diseases and are safer than ever before.
Unfortunately, there are still some very serious limitations to using BMT's; the two most severe are GVHD and failure to engraft. Both are potentially life-threatening. Another problem with standard BMTs is that patients have to have a donor that is a perfect "match"; this makes donors very hard to find. Statistically, there is only a 25% chance that even a brother or sister will be an adequate match as a donor. Due to these limitations, standard BMTs have significant morbidity and mortality, and only the sickest patients now undergo a standard BMT.
- The Institute's Approach to BMTs
The Institute's approach to BMT is based on a marrow processing technology, which removes the "bad" cells (which cause GVHD) but keeps the "good" cells (that help the new bone marrow engraft and produce healthy blood cells and a strong immune system). This breakthrough means that BMT can now be available for many patients who do not have a genetically matched donor needed for standard BMT.
- Partial Conditioning and Mixed Chimerism
It is sometimes necessary to completely destroy a patient's own bone marrow. This is the case, for example, with leukemia and other cancers involving the bone marrow itself. This is called "full ablation" and is done by giving the patient high doses of chemotherapy, radiation therapy, or both. Until the new donated bone marrow produces enough healthy cells, patients may become quite sick from the treatment itself and may develop infections or bleeding problems.
If a patient's immune system is only partially destroyed by the conditioning, this is called "partial conditioning". This means that the patient has both the donated bone marrow trying to produce immune cells to protect the body and, his or her own bone marrow doing the same thing. If both bone marrows survive and both produce the needed immune cells, this is called "chimerism" or "mixed chimerism". When both bone marrows produce immune cells that mature in one body, the two immune systems learn to recognize each other as part of the same body and do not attack each other. This is the goal of the Institute's partial conditioning approach to diseases that can be treated successfully with BMT if the complications and toxicity of standard BMT could be avoided.
The advantage of partial conditioning and chimerism is that it may be safer and less toxic than standard BMT. Patients do not usually become sick from the conditioning or the BMT, and their own bone marrow stays in place to protect them from infections and bleeding. This makes it possible to study the use of BMT to treat many new diseases, like sickle cell disease, multiple sclerosis, and non-malignant disorders.
Mixed chimerism may also be of benefit to persons who receive solid organ and islet cell transplants. When a person is given the bone marrow as well as the organ of another person, the recipient's body will recognize the organ as part of itself and the chances of rejection may be decreased.