A Bone Marrow Transplant (BMT) is the lay term for a complex medical procedure. The goal of this life-saving treatment is to replace a patient’s damaged or diseased blood-forming system with healthy stem cells. These specialized cells reside within the bone marrow and produce all types of mature blood cells, including red cells, white cells, and platelets. The procedure is reserved for serious conditions where a patient’s own bone marrow is defective or has been intentionally destroyed to eliminate a disease.
Conditions Treated by BMT
The procedure is employed to treat disorders falling into two main categories: malignant and non-malignant diseases. Malignant conditions often involve cancers of the blood and lymph system, such as certain leukemias, lymphomas, and multiple myeloma. For these cancers, the transplant serves to rescue the patient’s blood-forming system after high-dose chemotherapy or radiation is used to eliminate cancer cells.
Non-malignant disorders that necessitate a transplant include severe bone marrow failure syndromes, like aplastic anemia, or inherited blood disorders. Genetic conditions such as sickle cell disease and thalassemia are treated by replacing the patient’s defective blood-forming cells with healthy donor cells. Certain congenital immune deficiencies are also indications for this therapy, allowing for the reconstitution of a functional immune system.
Understanding Donor Types
Transplants are categorized by the source of the stem cells: autologous and allogeneic. An autologous transplant uses the patient’s own stem cells, which are collected before the high-dose treatment regimen and then returned to the body. This approach is chosen when the patient’s stem cells are healthy and the primary goal is to allow for the use of intensive therapy to eradicate a cancer like lymphoma or multiple myeloma.
An allogeneic transplant involves using stem cells from a donor, who may be a matched family member, an unrelated volunteer, or umbilical cord blood. This donor-based approach is required when the patient’s own cells are defective, such as in cases of genetic disease. It is also used when the patient needs the donor’s immune cells to fight residual cancer cells, a process called the graft-versus-tumor effect. The stem cells can be collected from three primary sources: the bone marrow directly, circulating peripheral blood, or umbilical cord blood.
Overview of the Transplantation Process
The transplantation process begins with the conditioning phase. This involves administering high-dose chemotherapy, with or without total body radiation, to the patient. The purpose of conditioning is threefold: to destroy any remaining cancer cells, to eliminate the patient’s existing, defective bone marrow, and to suppress the immune system to prevent rejection of the new cells in allogeneic transplants.
Following the conditioning phase, the new stem cells are delivered to the patient during the infusion phase. The stem cells are given intravenously, much like a standard blood transfusion, and they circulate in the bloodstream. The entire infusion process is quick, often lasting less than an hour.
The final stage is engraftment, where the infused stem cells travel through the bloodstream, settle in the bone marrow cavity, and begin to grow and multiply. Successful engraftment is confirmed when the absolute neutrophil count rises to a safe level, typically within two to four weeks post-infusion. During this period, the patient is highly vulnerable, as their own blood cell production has been intentionally suppressed, and the new cells are not yet fully functional.
Key Post-Transplant Complications
The heightened risk of infection is a serious concern after a transplant. During the pre-engraftment period, the patient experiences a severe lack of white blood cells, known as neutropenia, which leaves the body defenseless against bacteria, viruses, and fungi. This vulnerability persists until the new stem cells begin producing a sufficient number of immune cells.
A complication unique to allogeneic transplants is Graft-versus-Host Disease (GVHD). This occurs when the donor’s immune cells recognize the recipient’s body as foreign and launch an attack. The donor T-cells target tissues such as the skin, liver, and gastrointestinal tract, leading to symptoms ranging from mild rash to life-threatening organ damage. GVHD can appear acutely or as a chronic condition that persists for years.