Bone marrow transplantation involves the transfer of bone marrow, and therefore stem cells, to restore regular hematopoiesis. Bone marrow transplantation is generally indicated when the hematopoietic cell system has been severely compromised as a result of tumor disease or previous therapy (especially high-dose chemotherapy).
What is bone marrow transplantation?
Bone marrow transplantation involves the transfer of bone marrow, and therefore stem cells, to restore regular blood formation. Bone marrow transplantation (or BMT for short) is the replacement of damaged hematopoietic bone marrow (medulla ossium) with healthy bone marrow cells, which can generally be necessary after malignant tumor diseases and/or high-dose chemotherapy or radiation therapy. In general, a distinction is made between autologous bone marrow transplantation, in which the transplanted bone marrow material originates from the patient to be transplanted (autologous donation), and allogeneic bone marrow transplantation, which is used in most cases and in which the donor and recipient are not the same person (unrelated donation). Ideally, a so-called isologent bone marrow transplant can be performed, which is characterized by the fact that the cells to be transplanted come from a twin of the affected person.
Function, effect, and goals
In general, bone marrow transplantation is always necessary when the bone marrow, in which all blood cells are formed, is so damaged by disease or certain therapies that it can no longer perform this function. A significant impairment of bone marrow function can result primarily from malignant tumors such as lymphoma (cancer of the lymph glands) or leukemia (cancer of the blood) as well as solid tumor diseases. Likewise, pronounced autoimmune diseases, which lead to destruction of the body’s own structures as a result of a dysregulated immune system, may necessitate bone marrow transplantation. In addition, high-dose chemotherapy or radiotherapy measures have an increased risk of damaging the bone marrow. Prior to bone marrow transplantation, blood and urine levels are usually analyzed, the chest (thorax) is x-rayed, the abdomen and heart are examined sonographically, and an ECG (electrocardiogram) and EEG (electroencephalography) are performed to measure brain waves. In addition, a pulmonary function test and, in some circumstances, a computed tomography scan are common. On the basis of a bone marrow puncture, a tissue sample is taken in many cases and checked for matches of certain tissue characteristics such as human leukocyte antigens (HLA). Before substitution of the damaged bone marrow, it should be completely destroyed, especially in the case of malignant tumors, in order to avoid recurrences. This is usually achieved by high-dose chemotherapy with cytostatic drugs or by a combination of chemotherapy and radiotherapy. This pre-treatment, known as conditioning and lasting on average four to ten days, is followed by bone marrow transplantation. In allogeneic bone marrow transplantation, bone marrow material is harvested from the bone marrow or bone marrow stem cells are harvested from the donor’s blood (peripheral stem cell collection) and then infused into the recipient’s blood system via a vein. The infused healthy bone marrow cells enter the bone marrow via the blood system, settle and divide. If the therapy is successful, the newly settled bone marrow cells begin to synthesize blood cells on their own after a few weeks. An autologous bone marrow transplant (autologous marrow donation) is generally used when no suitable donor can be found. For this purpose, the patient’s own bone marrow is removed, processed and then frozen during a remission phase in which no new tumor cells are being formed. Following chemotherapy and radiotherapy pretreatment, the autologous bone marrow is returned to the affected person.
Risks, side effects, and hazards
Bone marrow transplantation is a highly stressful and severe surgical procedure that can result in life-threatening complications.Accordingly, bone marrow transplantation is usually performed only when all treatment alternatives have been exhausted and in the presence of a life-threatening underlying disease with good prospects of cure by surgery. A variety of complications can occur during the surgical procedure. For example, in rare cases, the transplanted bone marrow cells do not settle in the bone marrow of the recipient. In some cases, the transplanted cells mark tissue structures of the recipient as foreign and attack them. The skin, liver and/or intestine of the recipient are particularly affected. However, the reaction can be controlled by immunosuppressive drugs and, if necessary, counteracted in the event of overreactions. In addition, the risk of infectious diseases is greatly increased during the first three months after surgery, when the blood and immune systems are being rebuilt, and even a simple cold can be life-threatening for the patient. As a result of the chemotherapeutic pretreatment, the immunological knowledge of the defense system is destroyed, so that it must be reacquired. Protective vaccinations against tetanus, diphtheria or polio must be repeated accordingly. In addition, there is only a slight risk to the donor in bone marrow transplantation, which is derived from the usual hazards associated with anesthesia.
