Risks and benefits of bone marrow transplantation in children

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Overview of Bone Marrow Transplantation

Bone marrow transplantation, or hematopoietic stem cell transplantation (HSCT), is a therapeutic procedure utilizing allogeneic (donor-derived) or autologous (patient-derived) stem cells to treat a wide variety of malignant and nonmalignant conditions.
The procedure involves a preparative conditioning regimen utilizing chemotherapy and/or irradiation to eliminate the host's hematopoietic system, suppress the immune system to prevent rejection, and significantly reduce tumor burden in cases of malignancy.
The infused graft contains mature blood cells, including T cells, natural killer (NK) cells, and dendritic cells, which repopulate the recipient’s lymphohematopoietic system and provide a critical graft-versus-leukemia (GVL) effect by eliminating residual malignant cells.

Benefits and Clinical Indications

Malignant Disorders

In acute lymphoblastic leukemia (ALL), allogeneic HSCT benefits pediatric patients in their first complete remission if they exhibit high-risk features, or in second or subsequent remissions, achieving a 3-year overall survival rate of 70–80%.
For acute myeloid leukemia (AML), HSCT serves as a robust postremission consolidation therapy for high-risk patients, yielding better event-free survival than chemotherapy alone, with a 3-year overall survival of 60–70%.
HSCT is a proven curative treatment for chronic myelogenous leukemia (CML), with leukemia-free survival reaching 45–80%, though its upfront use is now generally reserved for patients who fail or cannot tolerate tyrosine kinase inhibitor therapy.
In juvenile myelomonocytic leukemia (JMML), HSCT cures approximately 50–60% of patients, overcoming the otherwise aggressive and rapidly fatal natural history of the disease.
For relapsed or refractory Hodgkin and non-Hodgkin lymphomas, as well as high-risk solid tumors like neuroblastoma and brain tumors, autologous HSCT offers survival rates of 50–60% for patients with sensitive disease and minimal tumor burden.

Non-Malignant Disorders

The most favorable HSCT outcomes are often achieved in non-malignant congenital or acquired disorders, as the risk of disease recurrence is extremely low and transplantation-related mortality is substantially reduced compared to malignant conditions.
HSCT is the definitive and potentially curative treatment for severe combined immunodeficiency (SCID), achieving a 95% survival rate when performed optimally within the first 100 days of life.
Other primary immunodeficiencies successfully cured by HSCT include Wiskott-Aldrich syndrome (where survival approaches 100% with a matched sibling), hyper-IgM syndrome, leukocyte adhesion deficiency, and chronic granulomatous disease (CGD).
For acquired severe aplastic anemia, matched-sibling bone marrow transplantation provides a long-term survival probability exceeding 80%.
Inherited bone marrow failure syndromes, such as Fanconi anemia, are cured of their aplastic anemia and protected from subsequent clonal hematopoietic disorders via HSCT, with a 5-year overall survival greater than 90% if performed prior to leukemic transformation.
HSCT is currently the only curative treatment for hemoglobinopathies; in thalassemia major patients without significant liver damage who have received regular iron chelation, the probability of survival with complete transfusion independence exceeds 90%.
In sickle cell disease, HSCT offers an 80–90% probability of cure for patients experiencing severe vasoocclusive crises or strokes, effectively halting disease progression.
For inherited metabolic diseases like mucopolysaccharidosis type 1 (Hurler syndrome) and adrenoleukodystrophy, HSCT enables the engraftment of microglial cells that deliver necessary enzymes directly to the central nervous system, preventing irreversible neurologic damage.

Risks and Complications

Graft-Versus-Host Disease (GVHD)

Acute GVHD is a major cause of morbidity and mortality, occurring when alloreactive donor T cells recognize recipient tissues as foreign, leading to a massive inflammatory attack primarily targeting the skin, liver, and gastrointestinal tract.
Significant acute GVHD develops in approximately 30% of matched sibling recipients and up to 60% of unrelated donor recipients, typically manifesting within the first 2 to 8 weeks post-transplant.
Severe (Grade IV) acute GVHD is a life-threatening and often fatal condition characterized by generalized erythroderma, severe liver impairment, and gross gastrointestinal bleeding or ileus.
Chronic GVHD occurs months to years after transplantation and represents the leading cause of nonrelapse mortality and morbidity in long-term survivors.
Chronic GVHD functions as a systemic disorder of immune regulation, producing severe autoimmune-like symptoms such as scleroderma, sicca syndrome, progressive bronchiolitis obliterans, and cirrhosis, which profoundly impact the patient's quality of life.

Infectious Complications

HSCT recipients experience a transient but profound state of immune deficiency, making life-threatening infections a leading risk.
In the preengraftment phase (the first 30 days), severe neutropenia and conditioning-induced mucosal damage place patients at extreme risk for bacterial sepsis and invasive fungal diseases caused by Candida and Aspergillus species.
In the postengraftment phase, delayed T-cell and B-cell recovery predisposes patients to severe viral infections, notably cytomegalovirus (CMV), Epstein-Barr virus (EBV), adenovirus, and varicella-zoster virus.
CMV pneumonia carries a massive case fatality rate of 85% in the absence of early antiviral treatment, while EBV reactivation can lead to fatal posttransplant lymphoproliferative disease (PTLD).

Graft Failure and Rejection

Primary graft failure (the failure to achieve a neutrophil count of 0.5 × 10^9/L) or secondary graft failure (the loss of peripheral counts after initial transient engraftment) exposes patients to a high risk of fatal infection.
Graft rejection is typically mediated immunologically by residual host T-lymphocytes surviving the conditioning regimen, and the risk is highest in HLA-disparate transplants, T-cell–depleted grafts, or when utilizing reduced-intensity conditioning regimens.

Venoocclusive Disease (VOD)

Also known as sinusoidal obstruction syndrome, VOD results from conditioning-induced endothelial damage within the liver.
It typically presents within 30 days of transplantation with marked hepatomegaly, right upper quadrant tenderness, jaundice, fluid retention, and ascites.
The severe form of VOD can rapidly progress to multiorgan dysfunction and carries a mortality rate exceeding 80% if untreated.

Late Effects and Organ Toxicity

Endocrine complications include severe growth impairment (particularly due to total body irradiation affecting the hypothalamic-pituitary axis and cartilage plates), primary ovarian or testicular failure, delayed puberty, and a high risk of permanent infertility.
Patients are at elevated risk for metabolic syndrome, dyslipidemia, and cardiotoxicity, especially if exposed to pre-transplant anthracyclines or chest radiation.
The risk of developing secondary malignancies, such as myelodysplastic syndromes, secondary leukemias, thyroid carcinoma, and brain tumors, is significantly elevated compared to the general pediatric population.
Neurocognitive deficits and progressive leukoencephalopathy can occur, particularly in young children who receive total body irradiation or cranial radiation.
Other long-term complications include restrictive pulmonary disease, renal toxicity, cataracts, dental abnormalities, and significant psychological late effects including depression, anxiety, and posttraumatic stress.