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Myeloproliferation, myeloaccumulation (decreased apoptosis), inflammation, bone marrow fibrosis and angiogenesis are cardinal features of the Philadelphia-negative chronic myeloproliferative neoplasms: essential thrombocythemia (ET), polycythemia vera (PV) and primary myelofibrosis (PMF). Histone deacetylases (HDACs) have a critical role in modulating gene expression and, accordingly, in the control of cell pathobiology and cancer development. HDAC inhibition has been shown to inhibit tumor growth (impaired myeloproliferation), to modulate the balance between pro- and antiapoptotic proteins in favor of apoptosis (enhanced apoptosis) and also to inhibit angiogenesis. Recently, enhanced HDAC enzyme activity has been found in CD34+cells from patients with PMF, enzyme activity levels highly exceeding those recorded in other chronic myeloproliferative neoplasms (CMPNs). The raised levels correlated to the degree of splenomegaly, suggesting that HDAC might be recruited as ET or PV progresses into myelofibrosis or PMF progresses into a more advanced stage. Accordingly, HDAC inhibition is an obvious novel therapeutic approach in these neoplasms. Using global gene expression profiling of whole blood from patients with CMPNs, we have found a pronounced deregulation of HDAC genes, involving significant up-regulation of the HDAC genes 9 and 11, with the highest expression levels being found in patients with ET (HDAC9 and 11), PMF (HDAC9) and CMPNs (both HDAC9 and HDAC11). Furthermore, we have identified that the HDAC6 gene is progressively expressed in patients with ET, PV and PMF, reflecting a steady accumulation of abnormally expressed HDAC6 during disease evolution. Our results lend further support to HDACs as important epigenetic targets in the future treatment of patients with CMPNs. Since the highest expression levels of HDAC genes were recorded in ET, in PMF and in the entire CMPN group, their down-regulation by HDAC inhibitors might be associated with decreased disease activity, including reduction of splenomegaly.

Gene expression profiling studies have unraveled deregulation of several genes that might be of pathogenetic importance for the development and phenotype of the Philadelphia-negative chronic myeloproliferative neoplasms. In the context of interferon-alpha2 as a promising therapeutic agent, we focused upon the transcriptional profiling of interferon-associated genes in patients with essential thrombocythemia (ET) (n = 19), polycythemia vera (PV) (n = 41), and primary myelofibrosis (PMF) (n = 9). Using whole-blood transcriptional profiling and accordingly obtaining an integrated signature of genes expressed in several immune cells (granulocytes, monocytes, B cells, T cells, platelets), we have identified a number of interferon-associated genes to be significantly deregulated but with a highly significant deregulation of interferon-inducible gene 27 (IFI27) (ET, PV, and PMF, fold change 8, 16, and 30, respectively). The striking deregulation of IFI genes may reflect a hyperstimulated but insufficient immune system being most enhanced in patients with advanced myelofibrosis, in whom the IFI27 gene displayed an exceedingly high expression. The interferon signature may reflect primary myelofibrosis as the burn-out phase of chronic inflammation which ultimately elicits clonal evolution and expansion owing to an exaggerated but incompetent antitumor immune response. Finally, IFI27 may be a novel biomarker of disease activity and tumor burden in patients with CMPNs., (© 2011 John Wiley & Sons A/S.)

The Philadelphia-negative chronic myeloproliferative neoplasms encompass essential thrombocythemia (ET), polycythemia vera (PV) and primary myelofibrosis (PMF). A major break-through in the understanding of the pathogenesis of these neoplasms occurred in 2005 by the discovery of the JAK2 V617F mutation in the large majority of patients with PV and in half of those with ET and PMF. A number of studies have shown that the "tumor burden" may be monitored at the molecular level in JAK2-positive patients using highly sensitive real-time quantitative PCR. During the last 25 years several studies have shown that interferon-alpha (IFN-alpha) induces complete haematological remissions in a large proportion of the patients. However, its use in clinical practice has unfortunately been limited due to side effects with high drop-out rates in most studies. Recently, IFN-alpha2 has been shown to induce deep molecular remissions and also normalization of the bone marrow in PV, which may be sustained even after discontinuation of IFN-alpha2 therapy. Accordingly, in the coming years we are most likely facing a new era of increasing interest for using IFN-alpha2 in the treatment of patients with PV, ET and the hyperproliferative phase of PMF. This paper reviews the history of IFN - in principle IFN-alpha2 - and its present status in the treatment of PV and related diseases. The role of IFN-alpha2 as immune therapy in the future treatment of CMPNs is highlighted and the rationale for the concept of minimal residual disease and potentially cure after long-term immune therapy with IFN-alpha2 is discussed and foreseen as an achievable goal in the future.

Chromosomal aberrations in polycythemia vera (PV) are heterogenous and nonrandom. A prognostic predictive value of these aberrations has not been established. The V617F mutation in the JAK2 gene on chromosome 9p24.1 was identified recently in peripheral blood leukocytes in the majority of patients with PV and in approximately half of patients with essential thrombocythemia and idiopathic myelofibrosis. Within the JAK2 V617F-positive PV patients, however, clinical presentation and degree of myeloproliferation varies to a great extent. Here we report four cases of chronic myeloproliferative disorders [two with PV, one with PV in transformation to idiopathic myelofibrosis (IMF) and one IMF patient], with the distinct karyotypic abberations der(18) t(9;18) (p13;p11) and der(9;18)(p10;q10). Two patients had hyperproliferative PV and two had "transitional PV" and IMF, respectively. All four patients harbored the JAK2 V617F mutation. Our data, together with previously published data, clearly indicate an association of these chromosomal abnormalities with a highly proliferative PV phenotype with a propensity to transform into postpolycythemic myelofibrosis. Cytogenetic analysis seems to identify a subgroup of patients with a distinct prognostic profile, and should be performed in conjunction with a JAK2 mutation analysis in patients suspected of a chronic myeloproliferative disease.

The identification of an acquired mutation of JAK2 in patients with myeloproliferative disorders has raised questions about the relationship between mutation-positive and mutation-negative subtypes, timing of the JAK2 mutation, and molecular mechanisms of disease progression. Here we demonstrate that patients with V617F(-) essential thrombocythemia do not commonly progress to become V617F(+). Consistent with the concept of distinct pathogenetic mechanisms, we show that patients with and without the JAK2 mutation have different patterns of cytogenetic abnormality, with virtually all patients carrying the 20q deletion or trisomy 9 being V617F(+). We also investigated the existence of a "pre-JAK2" phase by comparing the proportion of clonally derived granulocytes, estimated from X-chromosome inactivation patterns (XCIPs), with the proportion of V617F(+) granulocytes. Our results demonstrate that inherent XCIP variability between granulocytes and T cells produces a systematically biased pattern of results that may be misinterpreted as evidence for an excess of clonally derived granulocytes, an observation that limits the utility of XCIP analysis in this context. Lastly, we studied 4 patients with V617F(+) myeloproliferative disorders who subsequently developed acute myeloid leukemia. In 3 patients the leukemic cells were V617F(-), suggesting that in these patients the leukemia arose in a V617F(-) cell.

PRV-1 is a new molecular marker within the Ph-negative chronic myeloproliferative disorders. PRV-1 is a useful, highly sensitive and specific marker in the differentiation between polycythaemia vera (PV) and secondary erythrocytosis (ET), and seems to identify those PV patients presenting in the early phase of the disease with dominating thrombocytosis and thus a clinical phenotype of ET. These PRV-1 positive ET patients can be regarded as having "masked" PV or, more accurately, as having early PV. Moreover, PRV-1 positivity may be associated with a particular risk of thromboembolic complications. The biological role of PRV-1 and the significance of alterations in PRV-1 gene expression levels during treatment remain to be clarified.

The Philadelphia-negative chronic myeloproliferative disorders feature autonomous myeloid hyperproliferation and hypersensitivity to a number of growth factors, which most recently have been shown to be explained by a guanine-to-thymidine mutation in the Janus tyrosine kinase (JAK2) gene, implicating that phenylalanine is substituted with valine in position 617 (V617F mutation). JAK2 is of particular importance to haematopoiesis, since JAK2 proteins are activated mainly by the haematopoietic growth factors. The JAK2 mutation is present in most patients with polycythaemia vera and about 50% of patients with essential thrombocytosis and idiopathic myelofibrosis. The identification of the JAK2 mutation is a major molecular breakthrough in the understanding of the pathobiology of these disorders, and it is a new molecular marker to be used in the future classification of the diseases as well as a simple and rapid diagnostic test. The mutated JAK2 tyrosine kinase is an obvious potential target for a small-molecule inhibitor of tyrosine kinase activity.