Acute Myeloid Leukemia (AML) is a cancer originating in the bone marrow, characterized by the rapid growth of abnormal white blood cells. These cancerous cells interfere with the production of normal, healthy blood cells, leading to symptoms like fatigue and increased susceptibility to infection. A stem cell transplant (SCT), often called a bone marrow transplant, is an intensive therapeutic approach for AML. The goal of this complex, multi-stage procedure is to replace the diseased, cancer-containing bone marrow with healthy, blood-forming stem cells.
Determining the Need for a Transplant and Donor Selection
A stem cell transplant is reserved for patients with AML who are at a high risk of relapse after initial chemotherapy. This treatment is pursued after a patient achieves complete remission following induction therapy, or if the disease has returned. For individuals with intermediate or poor-risk genetic markers, an SCT offers the most potent anti-leukemic activity available. The decision to proceed involves weighing the curative potential of the transplant against the significant risks of the procedure itself.
The standard approach for AML is an allogeneic transplant, which uses stem cells collected from a healthy donor. This is primarily because the donor’s immune cells can recognize and attack any remaining leukemia cells, an effect known as graft-versus-leukemia. An autologous transplant, using the patient’s own cells, is rarely utilized for AML due to the risk of reintroducing cancer cells and the absence of this beneficial immune reaction. Allogeneic transplantation requires finding a suitable donor who can provide the cells.
Finding a suitable donor relies on matching Human Leukocyte Antigens (HLA), proteins found on the surface of most cells. The immune system uses these antigens to distinguish between “self” and “non-self,” making a close match essential to prevent the recipient’s body from rejecting the new cells. The best match is often a sibling, but many patients rely on national and international registries for a matched unrelated donor. Recent advancements allow the use of haploidentical donors, such as a parent or child who is only a half-match, significantly expanding the pool of potential donors.
The Three Stages of the Transplant Procedure
The transplant begins with the first stage, conditioning, a preparation phase designed to eliminate the existing diseased bone marrow. This phase typically involves administering high-dose chemotherapy, sometimes combined with total body irradiation (TBI). The purpose is to eradicate remaining leukemia cells and suppress the recipient’s immune system to prevent rejection of the donor cells. Regimens are tailored based on the patient’s health, categorized as either myeloablative (eliminating the bone marrow) or reduced-intensity (less toxic but still suppressive).
The second stage is the stem cell infusion, which is the actual “transplant day” and is similar to a simple blood transfusion. Healthy stem cells, collected from the donor’s bone marrow or peripheral blood, are administered intravenously. These cells circulate through the bloodstream until they find the bone marrow space. Once settled, they begin rebuilding the blood-forming system.
The third stage is engraftment, the period when the new donor stem cells take up residence and begin to mature. This process is confirmed when the patient’s blood counts start to rise, signaling successful production of white blood cells, red blood cells, and platelets. Engraftment usually occurs within two to three weeks after the infusion. During this time, the patient is monitored closely in the hospital to manage the profound drop in blood cell counts caused by conditioning.
Major Risks and Acute Complications
The procedure carries serious risks stemming from the intensity of the preparative regimen and the immediate introduction of a new immune system. The conditioning regimen can cause organ toxicity, affecting the liver, lungs, kidneys, and gastrointestinal tract. These effects are pronounced with myeloablative regimens. The loss of normal blood cells also leaves the patient with profound immunodeficiency, making them vulnerable to severe bacterial, viral, or fungal infections.
The primary complication of allogeneic SCT is Graft-versus-Host Disease (GVHD), which occurs when the donor immune cells (the graft) recognize the recipient’s body (the host) as foreign. These new immune cells then attack the patient’s healthy tissues. Acute GVHD typically develops within the first 100 days, often affecting the skin, liver, and gut, causing symptoms like a rash, jaundice, or severe diarrhea.
While mild GVHD can be beneficial due to its association with the graft-versus-leukemia effect, severe forms can be life-threatening. Prevention involves various immunosuppressive medications administered before and after the transplant. The goal is to balance immunosuppression: too much increases the risk of infection or relapse, while too little can lead to severe GVHD.
Long-Term Recovery and Survivorship
Following the acute phase, recovery transitions into a long-term process requiring continued monitoring for late effects. Chronic GVHD can develop months or years after the transplant, presenting as a condition similar to an autoimmune disorder that can affect almost any organ, including the eyes, mouth, skin, and lungs. Chronic GVHD significantly influences the quality of life and long-term outcomes for survivors.
Patients require long-term follow-up appointments to monitor for late effects, which are health issues that arise long after the transplant is complete. These effects can include:
- Cataracts.
- Avascular necrosis.
- Secondary cancers.
- Endocrine issues like diabetes.
For patients who are alive and disease-free two years post-transplant, the 10-year overall survival rate often exceeds 75%.
The risk of death in transplant survivors remains higher than in the general population, primarily due to chronic GVHD and the potential for late relapse of the AML. Long-term surveillance includes regular checks for minimal residual disease to detect the earliest signs of leukemia recurrence. Survivors often benefit from psychological and social support to improve their overall quality of life.