A prospective study of 338 patients with polycythemia vera: the impact of JAK2 (V617F) allele burden and leukocytosis on fibrotic or leukemic disease transformation and vascular complications.

We studied the relationship between JAK2 (V617F) mutant allele burden and clinical phenotype, disease progression and survival in patients with polycythemia vera (PV). The percentage of granulocyte mutant alleles was evaluated using a quantitative real-time polymerase chain reaction-based allelic discrimination assay. Of the 338 patients enrolled in this prospective study, 320 (94.7%) carried the JAK2 (V617F) mutation. Direct relationships were found between mutant allele burden and hemoglobin concentration (P=0.001), white blood cell count (P=0.001), spleen size (P=0.001) and age-adjusted bone marrow cellularity (P=0.002), while an inverse relationship was found with platelet count (P<0.001). During the study period, eight patients progressed to post-PV myelofibrosis (MF) (all carrying >50% mutant alleles), while 10 patients developed acute myeloid leukemia (AML). The mutant allele burden was significantly related to the risk of developing myelofibrosis (P=0.029) and retained its significant effect also in multivariable analysis (P=0.03). By contrast, the risk of developing AML as well as that of thrombosis was not significantly related to mutant allele burden. Leukocytosis did not affect thrombosis, MF, leukemia or survival. In conclusion, a JAK2 (V617F) allele burden >50% represents a risk factor for progression to MF in PV.

Immunophenotypic, cytogenetic and functional characterization of circulating endothelial cells in myelodysplastic syndromes.

Circulating endothelial cells (CECs) are associated with neoangiogenesis in various malignant disorders. Using flow cytometry, we studied CECs in 128 patients with myelodysplastic syndrome (MDS). MDS patients had higher CEC levels than controls (P<0.001), and an inverse relationship was found between CECs and international prognostic scoring system risk (r=-0.55, P<0.001). There was a positive correlation between marrow microvessel density and CECs, low-risk patients showing the strongest association (r=0.62, P<0.001). We calculated a progenitor-to-mature CEC ratio, which was higher in MDS patients than in healthy subjects (P<0.001), the highest values were found at diagnosis. CECs assessed by flow cytometry positively correlated with the ability to produce endothelial colony-forming cells in vitro (ECFCs; r=0.57, P=0.021), which was significantly higher in MDS patients than in controls (P=0.011). Fluorescence in situ hybridization analysis showed that a variable proportion of CECs (from 40 to 84%) carried the same chromosomal aberration as the neoplastic clone, while endothelial cells isolated from in vitro assays were negative. This study suggests that CECs reflect the abnormal angiogenesis found in MDS, especially in the early stages of the disease. The increased number of functional endothelial progenitor cells in MDS strengthens the rationale for therapeutic interventions aimed at restoring a normal interaction between hematopoietic progenitors and marrow microenvironment.

Flow cytometry evaluation of erythroid dysplasia in patients with myelodysplastic syndrome.

Erythroid dysplasia is the pathologic hallmark of myelodysplastic syndromes (MDS). To develop a quantitative flow-cytometry approach to its evaluation, we analyzed the expression of CD71, CD105, cytosolic H-ferritin (HF), cytosolic L-ferritin (LF) and mitochondrial ferritin (MtF) in erythroblasts from 104 MDS patients, 69 pathologic control patients and 19 healthy subjects. Six-parameter, 4-color flow cytometry was employed, and data were expressed as mean fluorescence intensity. Compared with pathologic and healthy controls, MDS patients had higher expression of HF (P < 0.001) and CD105 (P < 0.001), and lower expression of CD71 (P < 0.001). MtF was specifically detected in MDS with ringed sideroblasts, and there was a close relationship between its expression and Prussian blue staining (r = 0.89, P < 0.001). In vitro cultures of myelodysplastic hematopoietic progenitors showed that both HF and MtF were expressed at a very early stage of erythroid differentiation, and that MtF expression is specifically related to mitochondrial iron loading. A classification function based on expression levels of HF, CD71 and CD105 allowed us to correctly classify > 95% of MDS patients. This flow-cytometry approach provides an accurate quantitative evaluation of erythroid dysplasia and allows a reliable diagnosis of sideroblastic anemia, and may therefore be a useful tool in the work-up of patients with MDS.