A leading member of a number of international associations, and with more than 60 of his articles and papers published internationally, Yeditepe University Hospital’s Specialist in Hematology Prof. Dr. Hasan Atilla Özkan explains why the popular term ‘bone marrow transplantation’ can be misleading.
What is Bone Marrow?
Bone marrow is the spongy tissue in the interior of bones responsible for the production of blood cells. Cells within the bone marrow are unformed blood cells that can be transformed into red blood cells (erythrocytes), white blood cells (leukocytes) and platelets; red blood cells carry oxygen round the body, white blood cells are responsible for battling infections, while platelets control bleeding and coagulation.
Life depends on healthy bone marrow and blood cells, which certain diseases damage. In such cases, the most effective treatment is transplantation of the bone marrow, peripheral blood or cord blood, technically known as ‘Hematopoietic Stem Cell Transplantation’ (HSCT).
HSCT involves the exchange of unhealthy blood producing cells with healthy ones. The transplanted cells then begin to generate healthy erythrocytes, leukocytes and platelets.
Suitable HSCT candidates include patients with leukemia, myelodysplastic syndromes, Hodgkin’s lymphoma, non-Hodgkin’s lymphoma, multiple myeloma, some blood diseases and certain solid organ tumor cases.
Timing is crucial in HSCT procedures; early intervention renders better results. Transplant candidates will need to undergo tests for prognostic indicators and a special blood test for human leukocyte antigen (HLA). In HSCT procedures using stem cells obtained from the patient him/herself, the patient needs to avoid the use of chemotherapeutic agents that might damage stem cells.
HSCT is popularly known as a ‘bone marrow transplant’. This is actually an outdated and misleading expression.
Where Are The Stem Cells Sourced?
Hematopoietic stem cells can be sourced from the bone marrow, peripheral blood and umbilical cord blood. Except in certain cases, peripheral blood is used as a stem cell source. Growth factors are administered to patients (in autologous procedures), or donors, to direct the stem cells within the bone marrow to the peripheral blood. Then, a specialized device is used to collect the stem cells in a procedure called stem cell apheresis. Most of the collected stem cells are processed, frozen for storage under suitable conditions, and then thawed for transplantation on the day of the procedure.
In some cases, the collected stem cells are transplanted without processing and freezing. In both cases, the stem cells are intravenously transplanted from the peripheral blood. The transplanted cells begin to generate healthy erythrocytes, leucocytes and platelets.
Patients undergo a preliminary treatment known as a ‘preparative regimen’, which includes chemotherapy and/or radiotherapy. This serves to open up space in the bone marrow, to clear up remaining diseased cells, to ensure successful placement of the stem cells, and to reduce the risk of graft versus host disease (GVHD).
Recent advances have led to more frequent use of reduced dosage and reduced toxicity preparative regimens.
The selection of regimen must be patient-based and determined according to certain criteria relating to the nature of the transplant and the patient’s condition.
All three types of transplantation are carried out at Yeditepe University Hospital facilities:
Allogeneic transplantations (from a donor; known as Syngeneic when the donor is an identical twin) are typically used to treat bone marrow disorders such as leukemia, aplastic anemia and myelodysplastic syndromes, entailing high dosage chemotherapy and/or radiotherapy preparative regimens to eradicate the diseased bone marrow. Beneficially, the new immune system eliminates tumor cells -the ‘graft versus tumor effect’ (GvT). The main drawback is possible damage to the recipient’s normal tissue-GVDH. In syngeneic cases, both GvT and GVDH are eliminated.
Autologous transplantation (from the patient’s own stem cells) remains the preferred method in cases of lymphoma and multiple myeloma. A key advantage is a mortality rate of less than 3%. However, as well as the lack of any GvT, the possibility of post transplantation recurrence is higher, as diseased stem cells are present among those collected from the patient.
Donor selection, the determination of the correct preparative regimen, and post-transplantation care all require exceptionally high degrees of advanced technology, expertise and experience, which Yeditepe University Hospital has built up over many years to become a true reference center for the region.