Correlation of Novel Molecular Markers in Patients with Myeloproliferative Neoplasms.

Abstract 4968

Elucidation of the molecular aberrations underlying the development of myeloproliferative neoplasms (MPNs) has progressed rapidly during the previous years. In addition to the JAK2^V617F mutation, which is found in over 90% of patients with polycythemia vera (PV) and in around 50% of patients with essential thrombocythemia (ET) and primary myelofibrosis (PMF), several novel markers have recently been described. These include mutations in the Ten-Eleven-Translocation-2 (TET-2) gene, as well as overexpression of the hematopoietic transcription factor nuclear factor erythroid-2 (NF-E2). While the individual frequency of these abnormalities is well known, so far, studies that evaluate the relationship between these markers and their correlation with hematological parameters have not been conducted. The International Myeloproliferative Research Consortium (MPD-RC) has instituted a Tissue Bank (MPD-RC Trial 106) allowing the collection of MPN patient samples from member institutions in the US and Europe. Using this resource, we have investigated the relationship among the following molecular markers and hematological parameters in a series of 66 MPN patients: TET-2 mRNA expression, JAK2^V617F allele burden, NF-E2 mRNA expression, granulocyte clonality (female patients) as well as hematocrit, hemoglobin concentration, platelet numbers and leukocyte counts. Our crossectional cohort included 37 PV patients, 14 ET, 4 PMF and one post PV MF patient. Sixtyeight percent of the patients were treated, medication including hydroxyurea, anagrelide, ASA, interferon and one patient treated with imatinib mesylate. We acknowledge that treatment may affect the molecular markers being investigated. In addition, the desired effect of treatment on hematological parameters may not be paralleled by a similar effect on molecular markers. Therefore, investigation of treated patients may not reveal biological relationships present in untreated diseases states. We thus tested the effect of cytoreductive treatment on the expression of molecular markers by comparing treated and untreated patients in our cohort. The JAK2^V617F allele burden was significantly lower in treated patients than in untreated patients (p = 0.008). The same difference was noted when PV patients were analyzed alone (p = 0.006) In contrast, neither TET-2 nor NF-E2 mRNA expression were affected by treatment.

In the 66 MPN patients evaluated, a significant inverse Spearman correlation of -0.25 was noted between NF-E2 mRNA expression and hemoglobin concentration (p = 0.05). This relationship was more pronounced when PV patients were analyzed alone (Spearman's r = -0.41, p = 0.01). In addition, a correlation of 0.51 between JAK2^V617F allele burden and NF-E2 mRNA expression was noted (p = 0.0007). Occurrence of the recently discovered TET-2 gene mutations, which are present in around 15% of MPN patients, was measured indirectly by determining TET-2 mRNA expression. None of the other markers and parameters assessed was significantly correlated with the amount of TET-2 mRNA expressed.

We report a previously unrecognized inverse relationship between NF-E2 mRNA expression and hemoglobin concentration. These data complement several recent findings in MPN patients. While NF-E2 is overexpressed in granulocytes of all three MPN subtypes, PV, ET and PMF, its overexpression in CD34⁺ hematopoietic stem cells has so far only been observed in PMF. We have recently shown that ex vivo overexpression of NF-E2 in CD34⁺ hematopoietic stem cells drastically reduces erythroid colony formation. It was previously noted that mean JAK2^V617F allele burdens in PMF patients are higher than in PV or ET. Here, we confirm the previously noted positive correlation between JAK2^V617F allele burden and NF-E2 mRNA expression. Our data therefore suggest that high levels of JAK2^V617F in PMF patients directly or indirectly augment NF-E2 overexpression, which may contribute to the anemia of Primary Myelofibrosis.