Allogeneic Bone Marrow Transplantation
What is Allogeneic BMT?
‘Allogeneic’ BMT means transplantation of blood or bone marrow cells from "another individual’’. The bone marrow and the immune system of the patient is suppressed or destroyed by the use of high dose chemo-radiotherapy and replaced by the blood stem cells from another person. This is a more complex process compared to Autologous BMT involving correct selection of the donor, prevention of rejection of the blood stem cells or marrow of the donor (Graft Rejection) and prevention of attack from donor cells on the patient’s body (Graft-versus-host-disease, GVHD). At the same time the donor cells also attack the cancer cells producing a Graft-versus-Tumour Effect (GVT).
Who needs an Allogeneic BMT?
- Patients whose disease primarily involves the bone marrow: such as patients suffering from leukemia, myeloma, Thalassemia & Sickle Cell Anemia, Aplastic Anemia and Primary Immunodeficiency.
- Patients whose disease does not involve the bone marrow, but the disease is susceptible to a GVT effect: such as Lymphoma & some Metastatic Solid tumours.
- Patients whose disease does not involve the bone marrow, but is due to inherited deficiency of certain key enzymes which are produced by certain bone marrow derived cells: such as Hurler’s Disease, Gaucher’s Disease, Adrenoleukodystrophy etc.
What is the difference between Autologous and Allogeneic BMT
- Autologous BMT is a way of administering high doses of chemoradiotherapy to the patient which would otherwise irreversibly damage the bone marrow and subsequently rescuing the bone marrow function by infusing previously collected blood stem cells from the same patient. Whereas the main aim of Allogeneic BMT is to introduce a healthy marrow to replace the diseased marrow (as in Thalassemia, Aplastic anemia and leukemia) and introduce a new immune system which has the capability to fight infections (as in Primary immunodeficiency) and/ or fight the cancer cells remaining in the body after ‘ÇONDITIONING’ treatment with chemoradiotherapy.
- In Autologous BMT, the graft is rarely rejected as it belongs to the patient himself/herself, whereas in Allogeneic BMT, there is always a risk of graft rejection. Thus immunosuppressive drugs are given before and after allogeneic BMT which are not needed for Autologous BMT.
- GVHD is an accepted complication after Allogeneic BMT and not a part of Autologous BMT.
- Because of the above reasons, cure rate is much higher with Allogeneic BMT compared to Autologous BMT at the cost of a higher risk of complications or mortality.
- Due to the same reasons, the cost for Allogeneic BMT is higher than Autologous BMT.
How is a Donor selected for Allogeneic BMT
Donors for Allogeneic BMT are selected based on matching of HLA antigens
between the donor and the recipient.
The HLA antigens
are inherited as a set of 5 antigens from each parent called a ‘Haplotype
’. If both the haplotypes are matched between the donor and the recipient (patient), the donor is called a ‘Fully matched Donor
’. The chance of finding such a donor within the family is 20-30% and the chance of two unrelated persons matching with each other in both haplotypes is one in a million.
If one haplotype is matched between the patient and the donor, they are called HAPLOIDENTICAL
. Such a donor can only be selected from within the family. BMT from such a donor requires special expertise and infrastructure.
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