Bone marrow transplantation (BMT) is a special procedure for patients with certain cancers or other life-threatening diseases. BMT involves taking stem cells that are usually found in the bone marrow, filtering these cells, and giving them back to either the patient they were taken from or to any other person. The objective of BMT is to infuse healthy bone marrow cells into an individual after his/her own unhealthy bone marrow has been removed.
What is Bone Marrow?
Bone marrow is the soft, spongy tissue that is rich in stem cells found within the bones. The most primitive of these stem cells are the pluripotent stem cells (master cells), which are different from the other cells in the following aspects:
- They produce cells identical to themselves
- They have the capacity to produce one or more subsets of mature cells
These stem cells are of prime importance in Bone Marrow Transplantations.
Other sources of stem cells have gained popularity in the last decade, as their harvesting is better tolerated by patients while delivering almost identical success rates when compared to bone marrow transplants. These include peripheral blood stem cells and cord blood stem cells.
What conditions require BMT?
The conditions which necessitate a BMT can be broadly classified into 2 groups:
- Acute Myeloid and Lymphoblastic Leukemia
- Chronic Myeloid and Lymphoblastic Leukemia
- Hodgkin’s and Non-Hodgkin’s Lymphoma
- Myelodysplastic Syndrome
- Myeloproliferative Neoplasms, Primary Myelofibrosis, etc.
- Multiple Myeloma
- Aplastic Anaemia
- Haemoglobinopathies like Thalassemia and Sickle Cell Anaemia
- Immuno-deficiency disorders
- Congenital errors of metabolism
- Congenital storage disorders
What are the stages of a BMT?
Undergoing a Bone Marrow Transplant is a five-stage process.
- Physical examination – to assess the recipient’s health status
- Harvesting: the process of procuring stem cells to be used in the transplant
- Conditioning – preparing the body for transplant
- Transplanting the stem cells
- Recovery period
- Physical Examination
Routine diagnostic tests such as complete Haemogram, X-ray, and urinalysis are performed. In addition, HLA (Human Leukocyte Antigen) typing and blood grouping are done to evaluate recipient/donor compatibility. This compatibility evaluation is most vital to reduce the risk of transplant rejection.
- Harvesting the Cells from the Donor
- Autologous Bone Marrow Transplant: The donor is the patient himself. Stem cells are procured from the patient by either bone marrow harvest or apheresis (a process to collect peripheral blood stem cells), frozen, and later given back to the patient after a thorough treatment.
- Allogeneic Bone Marrow Transplant: The donor shares the same HLA type as the patient. Stem cells are procured by either bone marrow harvest or by apheresis from a genetically matched donor, generally a sister or brother.
Other donors for allogeneic bone marrow transplantations may include:
- A parent/relative: A haplo-identical match is when the donor is a parent and the genetic match is at least half identical to the recipient
- Unrelated bone marrow transplants. The stem cells or marrow are from an unrelated donor. For unrelated donors, national bone marrow registries are surfed.
- Peripheral Blood Stem Cell Transplant: This is routinely performed compared to the bone marrow harvest method as this procedure is easy to perform and less invasive. Some research studies even suggest that the stem cell yield by this method is higher when compared to bone marrow harvest. The process takes 4-6 hours after administering the necessary medication for 4 days.
Donors are injected with Granulocyte Colony Stimulating Factor (GCSF) for a duration of 4 days to stimulate stem cell proliferation.
The stem cells from the donor are collected using a process called apheresis and administered intravenously to the patient. The stem cells of the donor have the property of stem cell homing whereby they migrate to the bone marrow of the patient and override his/her defective stem cells. This restores the ability of bone marrow of the patient to produce normal blood elements.
- Umbilical Cord Blood Transplant: Umbilical cord blood is a very rich stem cell source. After delivery or birth of the infant, cord blood can be collected from the umbilical cord (which is a waste by-product of child birth) and preserved for later use. Cord blood has a higher concentration of stem cells compared to adult blood. About 80 to 100 ml cord blood is collected and such stem cells are perfectly suitable for transplants in children. The cord blood stem cells are typed, counted as well as tested before storage and preservation. Cord blood cells are frozen until required for transplant.
- Conditioning of the Patient
The conditioning procedure involves radiation (sometimes) and high doses of chemotherapy. It is carried out for three reasons:
- Destroying the existing bone marrow cells in order to make room for the transplanted stem cells
- Destruction of any existing cancer cells
- Suppression of activity of the immune system to decrease chances of rejection of donor stem cells
- Transplanting the Stem Cells
The Bone Marrow Transplant process does not involve the insertion of the marrow stem cells physically into the marrow of the recipient but is more of a delicate and intricate blood transfusion method. The stem cells that are harvested are administered through a central venous catheter into the bloodstream. From there these harvested stem cells find their way to the marrow by a property of stem cells known as stem cell homing.
- Recovery: The patient is monitored continuously to ascertain the success of the transplant. But, the procedure involves a few risks including:
- Graft versus host disease (GvHD): In this disease, the transplanted stem cells (“graft”) attack the recipient’s cells (‘host’) as they are considered alien to the body.
There are two types of GvHD:
- Acute GvHD – This occurs during the first three months after the transplant.
- Chronic GvHD – Develops from acute GvHD and can cause symptoms for many years.
- Infections as a consequence of chemotherapy and bone marrow suppression, the body is transiently unable to produce cells to combat infections.
As with any surgery/procedure like Bone Marrow Transplantation (BMT), prognosis and long-term survival may vary significantly from patient to patient. The number of transplantations being performed for an increasing number of diseases and ongoing medical developments has improved and the outcome for BMT in adults and children too. Constant follow-up care is necessary for the patient after a BMT. New procedures and methods to improve treatment therapies and reduce complications and side effects of transplantation are constantly being discovered.