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Bone marrow is the soft, spongy tissue located inside the bones which produce the blood cells: red and white blood cells and platelets. The marrow also contains unspecialized Hematopoietic Stem Cells. These cells can turn into many other types of cells such as bone marrow cells or any type of blood cell. Some cancers can prevent these stem cells from developing normally.
Bone Marrow Transplantation (BMT) is one of the complex medical procedures that are performed to treat both the benign and malignant disorders of the blood when the marrow is incapable of functioning properly. This can be due to chronic infections or cancer treatments like chemotherapy. Cancers are broadly divided into liquid cancers which affect the blood, and solid tumours. Liquid cancers are again categorized into leukaemia and lymphomas. Bone Marrow Transplantation is used to treat some common blood cancers such as acute marrow leukaemia, Lymphomas which have relapsed, and Multiple Myelomas.
Historically, the stem cells used in this process were collected from the bone marrow. But, now they are collected from the peripheral blood. So, BMT is more aptly referred to as Hematopoietic Stem Cell Transplantation. Contrary to popular perception, there is no painful surgery involved. Basically, the doctors collect the stem cells from a donor and after conditioning chemotherapy, where the diseased bone marrow cells are destroyed, they are transfused back into the recipient. The stem cells are mainly collected in two ways. One way is by collecting the peripherally mobilized stem cells after administering the growth factor, which brings the stem cells from the bone marrow to the periphery. These are then collected using an apheresis machine. By and large, this is a safe procedure the donor experiences little or no pain during the collection process and there are no short-term or long-term side effects resulting from it. In some disorders like bone marrow failures such as primary immunodeficiency disorders and aplastic anaemia, it is preferable to collect the stem cells from the bone marrow. In such cases, the donor is taken to an Operation Theatre and the stem cells are collected from the marrow after administering general anaesthesia.
There are mainly two types of BMT:
- Autologous Bone Marrow Transplant: The source of the stem cells is the patient themselves. The stem cells are harvested, or removed before the patient receives high-dose chemotherapy or radiation treatment which will destroy the bone marrow. After the treatment, the cells are returned to the body to make normal blood cells. The advantage of this method is that there are no adverse effects on immunity since the person’s own cells are returned and there are no foreign agents involved. However, this method can be used only if the person has healthy bone marrow.
- Allogeneic Bone Marrow Transplant: In this case, the stem cells are collected from another person called the donor. The donor must be a close genetic match. This is further divided into Matched Sibling Donor Stem Cell Transplantation wherein the patient’s own sibling gives the stem cells. Another way is Unrelated Stem Cell Transplantation, where a donor is an unrelated person. Since our country does not have a robust donor registry, sometimes a Half-Match or Haploidentical transplant is also carried out where the HLA is not identical but half-matched.
Some basic questions and answers about BMT are as follows:
- What happens after the stem cells have been transplanted into the patient?
BMT is a very complicated and intensive treatment. The doctor briefs the patient and the caregivers thoroughly regarding this procedure. The patient is given treatment to control the disease which may be refractory or relapsed as much as possible. This is called Salvage Therapy in Lymphomas. After this, the patient is taken to a highly sterile ward where they will be given conditioning chemotherapy to destroy the abnormalities in the bone marrow. The stem cells are then collected from a health-related or unrelated donor and are infused back into the patient. It may take about 3-4 weeks for those stem cells to go into the bone marrow and start making blood cells. During this period, the patient is kept under strict surveillance for any infections or complications. Once the patient is stable, walking around, and orally consuming food, he/she is discharged from the ward. The doctor maintains a close watch on the patient for about 60-90 days after the patient is discharged. This is because the first hundred days after the transplant are very critical.
- What are the possible side effects of BMT?
BMT toxicities can be classified into short-term and long-term toxicities. Short-term toxicities can be a result of the chemotherapy and include nausea, vomiting, ulcers in the mouth, severe pain, inability to taste food, loss of appetite, weight loss, diarrhoea, and other fungal and viral infections. But then, there are adequate medications to take the patients safely through the critical period.
In the long-term, in allogeneic transplantation, the stem cells can mount an immune attack in some cases. This is called Graft-versus-host disease (GVHD). In rare cases, it may affect their lungs, heart, etc. But with each passing year, Transplant-Related Mortality (TRM) has decreased from 30%-40% historically to 10%-20% in recent years.
- What diseases are treated most often using BMT?
Globally, the most common diseases treated using Bone Marrow Transplantation are Multiple Myeloma which is a common indicator for autologous transplantation, Acute leukaemia, which is a common indication for allogeneic transplantation, Aplastic Anaemia and Relapsed and Refractory Lymphomas. In Asia, Thalassemia accounts for a large number of transplants. There are certain rare immune disorders such as primary immunodeficiency disorders which can be cured using BMT.
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