Bone marrow failure syndromes and refractory cytopenia of childhood

__Abstract__ Hematopoiesis, or blood cell production, is sustained through hematopoietic stem cells, which are self-renewing cells that reside in the bone marrow, and that are capable of producing daughter cells that proliferate and mature to provide all adult blood effector cells, including erythrocytes or red blood cells, leukocytes or white blood cells, and thrombocytes or platelets. Erythrocytes are the most numerous cell types in the blood, and have as main task to transport oxygen through the lungs to peripheral tissues; leukocytes are responsible for elimination of bacteria and viruses, and thrombocytes for blood clotting. Hematopoiesis can be subdivided into myelopoiesis and lymphopoiesis. Myelopoiesis comprises the generation of granulocytes, monocytes, mast cells, mega- karyocytes (the precursors of thrombocytes), and erythrocytes. Lymphopoiesis encompasses the generation of B cells, T cells, and NK cells; collectively referred to as lymphocytes. Although recent insights suggest that cell fate determination during hematopoiesis is more plastic than previously thought, the classic, hierarchical model of determination of hematopoietic cell lineages is depicted in Figure 1 (adapted from Orkin and Zon

Bone marrow immunophenotyping by flow cytometry in refractory cytopenia of childhood

Refractory cytopenia of childhood is the most common type of childhood myelodysplastic syndrome. Because the majority of children with refractory cytopenia have a normal karyotype and a hypocellular bone marrow, differentiating refractory cytopenia from the immune-mediated bone marrow failure syndrome (very) severe aplastic anemia can be challenging. Flow cytometric immunophenotyping of bone marrow has been shown to be a valuable diagnostic tool in differentiating myelodysplastic syndrome from non-clonal cytopenias in adults. Here, we performed the first comprehensive flow cytometric analysis of immature myeloid, lymphoid cells and erythroid cells, and granulocytes, monocytes, and lymphoid cells in bone marrow obtained from a large prospective cohort of 81 children with refractory cytopenia. Children with refractory cyotopenia had a strongly reduced myeloid compartment, but not as severe as children with aplastic anemia. Furthermore, the number of flow cytometric abnormalities was significantly higher in children with refractory cytopenia than in healthy controls and in children with aplastic anemia, but lower than in advanced myelodysplastic syndrome. We conclude that flow cytometric immunophenotyping could be a relevant addition to histopathology in the diagnosis of refractory cytopenia of childhood. (The multi-center studies EWOG-MDS RC06 and EWOG-MDS 2006 are registered at clinicaltrials.gov identifiers 00499070 and00662090, respectively)

T-cell receptor Vβ skewing frequently occurs in refractory cytopenia of childhood and is associated with an expansion of effector cytotoxic T cells: A prospective study by EWOG-MDS

Immunosuppressive therapy (IST), consisting of antithymocyte globulin and cyclosporine A, is effective in refractory cytopenia of childhood (RCC), suggesting that, similar to low-grade myelodysplastic syndromes in adult patients, T lymphocytes are involved in suppressing hematopoiesis in a subset of RCC patients. However, the potential role of a T-cell-mediated pathophysiology in RCC remains poorly explored. In a cohort of 92 RCC patients, we prospectively assessed the frequency of T-cell receptor (TCR) b-chain variable (Vβ) domain skewing in bone marrow and peripheral blood by heteroduplex PCR, and analyzed T-cell subsets in peripheral blood by flow cytometry. TCRVβ skewing was present in 40% of RCC patients. TCRVβ skewing did not correlate with bone marrow cellularity, karyotype, transfusion history, HLA-DR15 or the presence of a PNH clone. In 28 patients treated with IST, TCRVβ skewing was not clearly related with treatment response. However, TCRVβ skewing did correlate with a disturbed CD4+/CD8+ T-cell ratio, a reduction in naive CD8+ T cells, an expansion of effector CD8 + T cells and an increase in activated CD8+ T cells (defined as HLA-DR+, CD57+ or CD56+). These data suggest that T lymphocytes contribute to RCC pathogenesis in a proportion of patients, and provide a rationale for treatment with IST in selected patients with RCC