Flow cytometric analysis of the expression of Fas/Fasl in bone marrow CD34+ cells in myelodysplastic syndromes: relation to disease progression.

The role of apoptosis in the pathobiology of myelodysplastic syndromes (MDS) remains controversial. We studied the expression of CD95 and CD95L in CD34+ cells of patients with newly diagnosed MDS by flow cytometry, and examined the relation between this expression and FAB and WHO types, total number of CD34+ bone marrow (BM) cells and the degree of peripheral cytopenias. The patients with refractory anemia (RA) and sideroblastic anemia showed CD34+ cells in numbers comparable to normal donors, but had a higher percentage of CD95/CD34 and CD95L/CD34 positive cells. An inverse correlation was found between these cells and the total CD34+ cells. This was also observed when only patients with RA were analyzed. In RAEB, however, CD95/CD95L expression correlated with CD34+ cells but not with the percentage of BM blasts. After classification by the WHO proposal, the patients with refractory cytopenias with multilineage dysplasia showed features intermediary between RA and RAEB. No significant correlation was seen between the expression of CD95/CD95L and the peripheral blood counts. These results are in keeping with the hypothesis that, as the number of MDS precursors increases during disease progression they become less succeptible to apoptosis.