Three consecutive related bone marrow transplants for juvenile myelomonocytic leukaemia

Juvenile myelomonocytic leukemia

Juvenile myelomonocytic leukemia (JMML), a rare myeloid malignancy that occurs in young children, is considered a clonal disease originating in pluripotent stem cells of the hematopoietic system. The pathogenesis of JMML involves disruption of signal transduction through the RAS pathway, with resultant selective hypersensitivity of JMML cells to granulocyte-macrophage colony-stimulating factor. Progress has been made in understanding aspects of the molecular basis of JMML. How these molecular mechanisms may lead to targeted therapeutics and improved outcomes remains to be elucidated. Allogeneic hematopoietic stem cell transplant is the only curative option for children with JMML, and it is fraught with frequent relapse and significant toxicity.

Juvenile myelomonocytic leukemia: molecular pathogenesis informs current approaches to therapy and hematopoietic cell transplantation

Juvenile myelomonocytic leukemia (JMML) is a rare childhood leukemia that has historically been very difficult to confidently diagnose and treat. The majority of patients ultimately require allogeneic hematopoietic cell transplantation (HCT) for cure. Recent advances in the understanding of the pathogenesis of the disease now permit over 90% of patients to be molecularly characterized. Pre-HCT management of patients with JMML is currently symptom-driven. However, evaluation of potential high-risk clinical and molecular features will determine which patients could benefit from pre-HCT chemotherapy and/or local control of splenic disease. Furthermore, new techniques to quantify minimal residual disease burden will determine whether pre-HCT response to chemotherapy is beneficial for long-term disease-free survival. The optimal approach to HCT for JMML is unclear, with high relapse rates regardless of conditioning intensity. An ongoing clinical trial in the Children's Oncology Group will test if less toxic approaches can be equally effective, thereby shifting the focus to post-HCT immunomanipulation strategies to achieve long-term disease control. Finally, our unraveling of the molecular basis of JMML is beginning to identify possible targets for selective therapeutic interventions, either pre- or post-HCT, an approach which may ultimately provide the best opportunity to improve outcomes for this aggressive disease.

Successful unmanipulated peripheral blood progenitor cell transplantation from an HLA haploidentical 2-locus-mismatched mother in a thalassemic patient with primary graft failure after transplantation of bone marrow and cord blood from unrelated donors

We report on a boy with beta-thalassemia major who developed early graft failure after double-unit unrelated cord blood transplantation, who subsequently received a myeloablative preconditioning regimen using non-T-cell-depleted PBSCT from his HLA-haploidentical 2-loci-mismatched mother. Neutrophil recovery with full donor chimerism was observed at post-transplantation day +11. Furthermore, GVHD was easy to control. The patient was transfusion-independent with complete donor chimerism eight months post-transplant. The result indicated that fetomaternal microchimerism may be an important attribute of a successful transplant. We suggested that a third allo-HSCT may be taken into consideration for patients with transfusion-dependent thalassemia who experience graft failure, even after two previous transplants.

Myelodysplastic and myeloproliferative disorders in children

PURPOSE OF REVIEW

Myelodysplastic and myeloproliferative disorders are clonal myeloid malignancies characterized by the triad of a growth advantage of clonal cells, disturbed differentiation and increased apoptosis. The rarity of these disorders in children and the lack of a widely accepted classification have contributed to the paucity of reports on these malignancies in the pediatric literature. A number of significant advances have been achieved in recent years. The present review will focus on diagnostics and therapy.

RECENT FINDINGS

International consensus has been achieved on classifying these disorders into three main groups; myelodysplastic syndrome (MDS), myeloid leukemia of Down syndrome (ML-DS) and juvenile myelomonocytic leukemia (JMML). In the last few years we have witnessed important advances, especially regarding the therapy of these disorders, and we have gained insights into the molecular pathogenesis of ML-DS and JMML.

SUMMARY

Classification of myelodysplastic and myeloproliferative disorders has been facilitated. Chemotherapy regimens for ML-DS have been reduced, resulting in fewer toxic deaths and improved survival. The results of stem-cell transplantation for MDS and JMML have improved. Insight into the molecular mechanisms involved may open new therapeutic avenues.