Cytogenetic and molecular genetic aspects of idiopathic myelofibrosis

Molecular Pathogenesis and Treatment Perspectives for Hypereosinophilia and Hypereosinophilic Syndromes

Hypereosinophilia (HE) is a heterogeneous condition with a persistent elevated eosinophil count of >350/mm³, which is reported in various (inflammatory, allergic, infectious, or neoplastic) diseases with distinct pathophysiological pathways. HE may be associated with tissue or organ damage and, in this case, the disorder is classified as hypereosinophilic syndrome (HES). Different studies have allowed for the discovery of two major pathogenetic variants known as myeloid or lymphocytic HES. With the advent of molecular genetic analyses, such as T-cell receptor gene rearrangement assays and Next Generation Sequencing, it is possible to better characterize these syndromes and establish which patients will benefit from pharmacological targeted therapy. In this review, we highlight the molecular alterations that are involved in the pathogenesis of eosinophil disorders and revise possible therapeutic approaches, either implemented in clinical practice or currently under investigation in clinical trials.

Effect of concentration of platelet-derived growth factor on proliferative activity of human fibroblasts

Serum concentration of platelet-derived growth factor was measured in patients with trophic ulcers and proliferative activity of human fibroblasts was measured in wells with different content of added serum platelet-derived growth factor. In parallel, morphofunctional analysis of platelets from the whole blood of these patients was performed. A close correlation was found between morphofunctional parameters of blood platelets and serum concentration of platelet-derived growth factor. Platelet-derived growth factor in concentrations below 150 pg per well stimulated fibroblast proliferation and preserved their viability. Platelet-derived growth factor in concentrations >200 pg per well suppressed fibroblast proliferation and impaired their viability.

Evaluation of 13q14 status in multiple myeloma by digital single nucleotide polymorphism technology

Chromosome 13q deletions are common in multiple myeloma and other cancers, demonstrating the importance of this region in tumorigenesis. We used a novel single nucleotide polymorphism (SNP)-based technique, digital SNP (dSNP), to identify loss of heterozygosity (LOH) at chromosome 13q in paraffin-embedded bone marrow biopsies from 22 patients with multiple myeloma. We analyzed heterozygous SNPs at 13q for the presence of allelic imbalances and examined the results by sequential probability ratio analysis. Where possible, dSNP results were confirmed by fluorescence in situ hybridization. Using dSNP, we identified 13q LOH in 16/18 (89%) (95% Confidence Interval; 65%, 99%) patients without the need for neoplastic cell enrichment. In 8/16 (50%) cases, either partial or interstitial patterns of LOH were observed. Both fluorescence in situ hybridization and dSNP data proved concordant in just 3/9 cases. Five of the six discrepancies showed LOH by dSNP occurring beyond the boundaries of the fluorescence in situ hybridization probes. Our findings show that dSNP represents a useful technique for the analysis of LOH in archival tissue with minimal infiltration of neoplastic cells. The high-resolution screening afforded by the dSNP technology allowed for the identification of complex chromosomal rearrangements, resulting in either partial or interstitial LOH. Digital SNP represents an attractive approach for the investigation of tumors not suitable for genomic-array analysis.

Epigenetic alterations complement mutation of JAK2 tyrosine kinase in patients with BCR/ABL-negative myeloproliferative disorders

An acquired autoactivating mutation with a V617F amino-acid substitution in the JAK2 tyrosine kinase is frequently found in BCR/ABL-negative myeloproliferative disorders (MPD). Hypermethylation of CpG islands within gene promoter regions is associated with transcriptional inactivation and represents an important mechanism of gene silencing in the pathogenesis of hematopoietic malignancies. In this study, we determined the DNA methylation status of 13 cancer-related genes in the context of JAK2 mutations in 39 patients with MPD. Genes analyzed for hypermethylation were SOCS-1, SHP-1, E-cadherin, MGMT, TIMP-2, TIMP-3, p15, p16, p73, DAPK1, RASSF1A, RARbeta2 and hMLH1. We found at least one hypermethylated gene in 15/39 MPD patient specimens, and in 6/39 samples aberrant methylation of the negative cytokine regulator SOCS-1 was present. The JAK2V617F mutation was found in 21/39 patients as determined by allele-specific polymerase chain reaction. Hypermethylation of SOCS-1 was observed in 3/21 patients with an autoactivating JAK2 mutation and in 3/18 patients with wild-type JAK2. Our results suggest that epigenetic inactivation of SOCS-1 may be a complementary mechanism to the JAK2V617F mutation in the pathogenesis of MPD that leads to dysregulation of JAK-STAT signal transduction and thus contributes to growth factor hypersensitivity.

Advances in the therapy of chronic idiopathic myelofibrosis

The molecular basis of chronic idiopathic myelofibrosis (CIMF) has remained elusive, thus hampering the development of effective targeted therapies. However, significant progress regarding the molecular mechanisms involved in the pathogenes is of this disease has been made in recent years that will likely provide ample opportunity for the investigation of novel therapeutic approaches. At the fore front of these advances is the discovery that 35%-55% of patients with CIMF harbor mutations in the Janus kinase 2 tyrosine kinase gene. Until very recently, the management of patients with CIMF involved the use of supportive measures, including growth factors, transfusions, or interferon, and the administration of cyto-reductive agents, such as hydroxyurea and anagrelide. However, several trials have demonstrated the efficacy of antiangiogenic agents alone or in combination with corticosteroids. In addition, the use of reduced-intensity conditioning allogeneic stem cell transplantation has resulted in prolonged survival and lower transplant-related mortality.

Trisomy 8 in prefibrotic early stages of chronic idiopathic myelofibrosis: a fluorescence in situ study of bone marrow biopsies

Repeatedly performed bone marrow biopsies were studied in 30 patients with chronic idiopathic myelofibrosis (CIMF) by fluorescence in situ hybridization to detect and quantify trisomy 8 anomaly during the evolution of disease. For the establishment of threshold values we used negative and positive control specimens. At least 500 cells were evaluated in each specimen and only nuclei with three distinctive signals were regarded as positive. According to the controls, 27 patients revealed false-positive signals ranging from 0 to 1.2% (0.88 +/- 1.12). On the other hand, 3 patients showed an incidence of more than 6.5% (up to 10.1%) in the initial prefibrotic as well as advanced fibro-osteosclerotic stages of CIMF. In conclusion, trisomy 8 has been demonstrated already in the prodromal stages of CIMF and therefore is not limited to classical fibro-osteosclerotic manifestations.

Abnormalities of GATA-1 in megakaryocytes from patients with idiopathic myelofibrosis

The abnormal megakaryocytopoiesis associated with idiopathic myelofibrosis (IM) plays a role in its pathogenesis. Because mice with defective expression of transcription factor GATA-1 (GATA-1(low) mutants) eventually develop myelofibrosis, we investigated the occurrence of GATA-1 abnormalities in IM patients. CD 34(+) cells were purified from 12 IM patients and 8 controls; erythroblasts and megakaryocytes were then obtained from unilineage cultures of CD 34(+) cells. Purified CD 61(+), GPA(+), and CD 34(+) cells from IM patients contained levels of GATA-1, GATA-2, and FOG-1 mRNA, as well as of GATA-2 protein, that were similar to controls. In contrast, CD 61(+) cells from IM patients contained significantly reduced GATA-1 protein. Furthermore, 45% of megakaryocytes in biopsies from IM patients did not stain with anti-GATA-1 antibody, as compared to controls (2%), essential thrombocythemia (4%), or polycythemia vera (11%) patients. Abnormalities in immunoreactivity for FOG-1 were not found, and no mutations in GATA-1 coding sequences were found. The presence of GATA-1(neg) megakaryocytes in bone marrow biopsies was independent of the Val 617 Phe JAK 2 mutation, making it unlikely that a downstream functional relationship exists. We conclude that megakaryocytes from IM patients have reduced GATA-1 content, possibly contributing to disease pathogenesis as in the GATA-1(low) mice and also representing a novel IM-associated marker.

Idiopathic myelofibrosis with generalized periostitis in a 4-year-old girl

Idiopathic myelofibrosis, a chronic myeloproliferative disorder of unknown origin, is characterized by splenomegaly, extramedullary hematopoiesis, leukoerythroblastosis, teardrop erythrocytes, and myelofibrosis. It is a rare disorder in childhood. The authors describe a 4-year-old girl with features consistent with idiopathic myelofibrosis, who also had generalized solid laminated periosteal reaction involving all long bones. The presence of thrombocytopenia at the onset and lack of leukocytosis were in contrast to the reported features seen in children. Recent case reports describe a relatively indolent course in children. Spontaneous remissions have also been described in pediatric cases. The fulminant course of this patient without any features of malignant transformation was noteworthy in this regard.

Long-term follow-up of a patient with idiopathic myelofibrosis associated with chromosome 11 and 13 abnormalities

A case of a leukemic transformation following a 27-year history of idiopathic myelofibrosis (IMF) is presented. The patient had two chromosomal abnormalities: a deletion of chromosome 13, del 13(q12q14), and a deletion of chromosome 11, del 11(q14q23). This patient's final diagnosis was acute micromegakaryocytic leukemia, and she died 1 month after leukemic transformation with an additional chromosomal abnormality, trisomy 8. IMF with myeloid metaplasia associated with deletion of the long arms of chromosomes 11 and 13 has not been previously reported. We speculate that the leukemic transformation in this patient was associated with chromosomal abnormalities del 11 and trisomy 8.

Impaired GATA-1 expression and myelofibrosis in an animal model

The genetic lesion(s) underlying chronic idiopathic myelofibrosis, as well as the mechanisms leading to the typical fibro-osteosclerotic changes of the bone marrow microenvironment, are still undefined. Recently, animal models of the disease have been described. We will briefly review the characteristics of these models, the thrombopoietin-overexpressing mice and the GATA-1(low) mice (mice deficient for GATA-1 expression in megakaryocytes), and illustrate how they provided insights into pathogenetic mechanisms of myelofibrosis, with special regard to the role of abnormal megakaryocyte proliferation and maturation.

TGF-beta1 induces bone marrow reticulin fibrosis in hairy cell leukemia

The mechanisms that lead to reticulin fibrosis of bone marrow (BM) in hairy cell leukemia (HCL) are not fully understood. We therefore investigated the involvement of TGF-beta1, a potent fibrogenic cytokine, in this process. Immunoassays revealed that TGF-beta1 is present at higher concentrations in BM, serum, and plasma of HCL patients in comparison with healthy donors (P < 0.001). RT-PCR and immunofluorescence studies showed that TGF-beta1 is overexpressed at the mRNA and protein levels in peripheral blood, spleen, and BM mononuclear cells and that hairy cells (HCs) are the main source of TGF-beta1. Active TGF-beta1 correlated significantly with grades of BM fibrosis, infiltration with HCs, and serum procollagen type III aminoterminal propeptide (PIIINP). Ex vivo studies demonstrated that TGF-beta1 significantly enhances the production and deposition of reticulin and collagen fibers by BM fibroblasts. In addition, BM plasma of HCL patients increased the synthesis of type I and type III procollagens, the main components of reticulin fibers, at the mRNA and protein levels. This fibrogenic activity of BM plasma was abolished by neutralizing anti-TGF-beta1 antibodies. These results show, for the first time to our knowledge, that TGF-beta1 is highly expressed in HCs and is directly involved in the pathogenesis of BM reticulin fibrosis in HCL.

Transplant strategies for idiopathic myelofibrosis

Idiopathic myelofibrosis (IMF) is a clonal stem cell disorder and is one of the four major myeloproliferative disorders, which include essential thrombocythemia (ET), polycythemia vera (PV), and chronic myelogenous leukemia (CML). Patients may be asymptomatic at the early stages, but later progress to marrow fibrosis, splenomegaly with pancytopenia leading to anemia, and other constitutional symptoms. Most of the care available is supportive and only palliates the constitutional symptoms. Prognosis for these patients is dependent on karyotype, hemoglobin count, and age. Stem cell transplantation is the only curative therapy, which results in eradication of the stem cell clone, with the cessation of extramedullary hematopoiesis and resolution of marrow fibrosis and its sequelae. Stem cell replacement therapy using either autologous or allogeneic stem cells has been attempted in small populations of patients with variable benefit. A nonmyeloablative approach has shown promise in a very small number of patients, but additional investigation is required for the ideal management of these patients.

Dysregulation and overexpression ofHMGA2in myelofibrosis with myeloid metaplasia

Among cytogenetic studies of patients affected with myelofibrosis with myeloid metaplasia (MMM), a rare chronic myeloproliferative disorder, we found several reports of structural abnormalities of the long arm of chromosome 12. Two MMM patients had a balanced translocation involving 12q: t(4;12)(q32;q15) and t(5;12)(p14;q15), respectively. FISH (fluorescence in situ hybridization) analysis showed that BAC (bacterial artificial chromosome) RP11-366L20 overlaps the breakpoint in both cases. A gene, HMGA2, most of which is included in that BAC, thus was identified as a potential candidate. Using reserves transcriptase-polymerase chain reaction (RT-PCR), we looked for expression of HMGA2 in blood mononuclear cells from these 2 patients and demonstrated a transcript in both. Moreover, we found the gene expressed in the hematopoietic cells of 10 of 10 additional patients bearing no 12q anomalies. HMGA2, not expressed in normal subjects, is implicated in benign solid tumors such as lipomas, leiomyomas, and other rare tumors of mesenchymal origin. We postulate that its dysregulation and overexpression in myeloid progenitors contribute also to the pathogenesis of MMM.

Myelofibrosis with myeloid metaplasia

MMM is a chronic myeloproliferative disorder characterized by bone marrow fibrosis and neoangiogenesis, constitutive release ofa high number of CD34+ stem cells from the bone marrow, and extramedullary hematopoiesis. It presents with heterogeneous clinical features in which anemia and progression to symptomatic splenomegaly dominate. The pathogenesis is undefined, but the dual action of deregulation of the bFGF pathway may influence myeloproliferation, myelofibrosis, and neoangiogenesis. Animal models suggest that chronic exposure to high doses of thrombopoietin or impairment of the capacity of megakaryocytes to differentiate into platelets, as occurs in the GATA-1(low) mice, is a necessary event for myelofibrosis. Allogeneic stem cell transplantation offers a chance of cure, and low conditioning regimens may extend the age of transplantable patients with lower mortality. Autologus stem cell transplantation and splenectomy are risky procedures that may be considered in patients with advanced disease when conventional therapies for correcting anemia (danazol, recombinant human erythropoietin, or cyclosporine) or chemotherapy for splenomegaly and myeloproliferation (hydroxyurea or interferon alfa) have failed. Thalidomide has been tested in numerous series, and its capacity to improve anemia and thrombocytopenia while reducing splenomegaly has been documented.