Bone marrow is a soft, fatty and spongy tissue inside the bones. The bone marrow contains hemato-poetic stem cells, which means they have the ability to mature and differentiate into specific types of blood cells like, RBC, WBC and platelets. Bone marrow of the hip bone, breast bone, ribs, and skull are responsible for producing blood cells in our body.
Bone marrow transplant is a procedure to replace the unhealthy or damaged bone marrow cells of the patient with the healthy ones. This is called as stem cell transplant because the transplanted stem cells from bone marrow develop into blood cells when transferred in the host body.
The transplant is done in case the normal marrow cells in the body of recipient are not functioning properly. This may be because of a chronic infection, cancer, some disorders like sickle cell anaemia, thalassemia and certain diseases which affect bone marrow like sickle-cell anaemia, aplastic anaemia, and congenital neutropenia (birth defect).
The process of transplanting bone marrow cells usually take place in three basic steps-
1. Autologous transplant: In this, the healthy bone marrow stem cell are taken from the recipient only and are infused in the body after chemo or radiation treatment which kill unhealthy cells.
2. Allogeneic transplant: In this type of transplant, healthy bone marrow cells are extracted who a donor with compatibility and transferred into the recipient. The new transplanted cells then make healthy blood cells in the body.
3. Umbilical cord transplant: Here the donated stem cells come from the new born baby’s umbilical cord which is preserved at the time birth. But these stem cells are the perfect match and at a very immature stage, therefore it takes more time for them to develop into healthy blood cells.
Harvesting the healthy stem cells from bone marrow
The hemato-poetic stem cells can be extracted from different sources depending on the kind of bone marrow transplant. Apheresis (Leukapheresis) is the procedure in which the blood of the person is drawn suing a needle and passed through a machine which detects stem cells and sends back rest of the blood back into the person. This can be done in case of autologous, where the blood of the recipient only is used and preserved by freezing and for allogeneic as well where the donor blood can be used and storage may not be required. Another way is to extract the cells directly from bone marrow in the hip bone through a needle, and the amount depends on recipient’s weight. The donor is put under a local anaesthesia during the process and may need to stay in the hospital for 24 hours. These are pain free procedures. In case of allogeneic transplant, HLA (Human Leukocyte Antigen) testing has to be done to match the donor. The chance of better engraftment increases with the number of antigens matched. Another source is umbilical cord which is donated by the mother at the time of her baby’s birth.
Chemotherapy and conditioning of body before the transfer
The patient has to undergo chemotherapy with or without the radiation to kill the unhealthy bone marrow or cancerous cells. The healthy bone marrow cells also gets killed in the process. The new transplanted cells replace these cells and perform normal function in their place.
Transplanting healthy bone marrow stem cells into the recipient
After the chemotherapy, which takes a few days, the patient is ready for the transplant which is a simple procedure. An IV tube is put into the recipient and stem cells are transferred through thin tubes called catheters. It takes only few hours to transplant the stem cells and is a painless procedure. It takes some time for blood cell levels to climb up and reach the optimum. Generally, the procedure is safe and some symptoms may arise when the preserved cells are transferred. Also, there is a risk of rejection in case of donor cells.
Minor side effects can happen, especially in case of preserved cells, which include:
Weird taste in the mouth