Does primary myelofibrosis involve a defective stem cell niche? From concept to evidence.

Primary myelofibrosis (PMF) is the rarest and the most severe Philadelphia-negative chronic myeloproliferative syndrome. By associating a clonal proliferation and a mobilization of hematopoietic stem cells from bone marrow to spleen with profound alterations of the stroma, PMF is a remarkable model in which deregulation of the stem cell niche is of utmost importance for the disease development. This paper reviews key data suggesting that an imbalance between endosteal and vascular niches participates in the development of clonal stem cell proliferation.

Cellular and molecular mechanisms underlying bone marrow and liver fibrosis: a review.

Chronic fibroproliferative diseases are an important cause of morbidity and mortality in the world. Fibrotic diseases occur in a large variety of vital organs, and the process of fibrosis seems common to all tissues. In all of fibrotic reactions, the underlying cellular and molecular mechanisms involve leukocyte infiltration, the persistence of inflammation in the tissue, and the proliferation of cells with a myofibroblast phenotype.

Stem cell dysregulation in myelofibrosis with myeloid metaplasia: current data on growth factor and transcription factor involvement.

Myelofibrosis with myeloid metaplasia (MMM), the rarest Philadelphia chromosome-negative chronic myeloproliferative disorder (MPD), is characterized by extramedullary hematopoiesis and myelofibrosis. The primary molecular defect leading to the clonal amplification of the hematopoietic progenitors is still unknown. In this review, we will focus on current data in favor of a pivotal role for hematopoietic and fibrogenic growth factors and of transcription factors in the dysregulation of the hematopoietic compartment.

Altered transcription of the stem cell leukemia gene in myelofibrosis with myeloid metaplasia.

An increased number of circulating CD34+ hematopoietic progenitors with a prominent proliferation of the megakaryocytic (MK) population are the hallmarks of the myeloproliferation in myelofibrosis with myeloid metaplasia (MMM). Analyzing the potential contribution of the stem cell leukemia (SCL) gene in MMM myeloproliferation was doubly interesting for SCL is expressed both in primitive-uncommitted progenitor cells and erythroid/MK cells, its transcription differentially initiating from promoter 1b and 1a, respectively. Our results show that: (i) the expression of SCL transcript is increased in peripheral blood mononuclear cells (PBMCs) from patients; (ii) SCL gene transcription is altered in MMM CD34+ progenitor cells sorted into CD34+CD41+ and CD34+CD41- subpopulations.

Critical review of pathogenetic mechanisms in myelofibrosis with myeloid metaplasia.

Myelofibrosis with myeloid metaplasia is an uncommon chronic myeloproliferative disorder characterized by extramedullary hematopoiesis associated with varying degrees of bone marrow fibrosis (hematopoiesis is clonal and fibrosis is a polyclonal reactive process). The primary defect in a pluripotent stem cell is still unknown. However, advances have been made during the past few years in the knowledge of the pathogenetic mechanisms in this disorder.

Involvement of the fibrogenic cytokines, TGF-beta and bFGF, in the pathogenesis of idiopathic myelofibrosis.

Idiopathic Myelofibrosis (IMF), is a chronic myeloproliferative disorder characterized by the association of myeloproliferation and myelofibrosis. The pathophysiological mechanisms resulting in this disease remain still unclear. The myeloproliferation appeared to result from the clonal amplification of hematopoietic progenitors.

Lack of interferon-alpha-induced tyrosine phosphorylation of Vav proto-oncogene in patients with myelofibrosis with myeloid metaplasia.

Myelofibrosis with myeloid metaplasia (MMM) is an uncommon chronic myeloproliferative disorder characterized by clonal stem cell proliferation and reactive non-clonal proliferation of bone marrow fibroblasts with fibrosis. In the absence of curative therapy, the current management for the majority of patients is directed towards alleviation of symptoms and improvement in quality of life. A number of experimental therapies have been investigated, among which is the use of type I interferon (IFN)-alpha, whose overall results are disappointing.

p95(vav) associates with the type I interferon (IFN) receptor and contributes to the antiproliferative effect of IFN-alpha in megakaryocytic cell lines.

The vav proto-oncogene product is a 95 kDa protein predominantly expressed in hematopoietic cells. Vav presents a wide range of functional domains, including structural domains known to be involved in signal transduction. Triggering of various cytokine receptors among which type I interferon receptor induces a rapid and transient tyrosine phosphorylation of p95(vav).

Dual implication of fibrogenic cytokines in the pathogenesis of fibrosis and myeloproliferation in myeloid metaplasia with myelofibrosis.

Though the diagnostic criteria of myeloid metaplasia with myelofibrosis (MMM) are now well established, the origin and pathophysiological mechanisms of this myeloproliferative disorder remain unclear. Concerning its pathophysiology, myeloproliferation and myelofibrosis are the intrinsic characteristics of the disease. Whereas the myeloproliferation was shown to result from a clonal amplification of primitive progenitor cells, fibroblast proliferation appeared to be polyclonal, thus suggesting that myelofibrosis was a reactive process.

Elevated levels of basic fibroblast growth factor in megakaryocytes and platelets from patients with idiopathic myelofibrosis.

Idiopathic myelofibrosis, or agnogenic myeloid metaplasia, is a chronic myeloproliferative disorder characterized by clonal expansion and marrow fibrosis. Although marrow fibrosis appears to be a reactive process, it substantially contributes to impaired haemopoiesis. During the last few years the implication of megakaryocyte-derived growth factors in its pathogenesis has been documented.

Differential expression of transforming growth factor-beta, basic fibroblast growth factor, and their receptors in CD34+ hematopoietic progenitor cells from patients with myelofibrosis and myeloid metaplasia.

Myelofibrosis with myeloid metaplasia (MMM) is a myeloproliferative disorder characterized by clonal expansion of hematopoiesis and marrow fibrosis. Previous results from our group have shown an increased production of two potent fibrogenic factors also involved in the regulation of primitive hematopoietic cells, namely transforming growth factor-beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF), in patients with MMM. It is likely to assume that the myeloproliferation characteristic of this disease may result from an abnormal proliferation of CD34+ hematopoietic progenitors.

TGF-beta and megakaryocytes in the pathogenesis of myelofibrosis in myeloproliferative disorders.

Myeloproliferative disorders are clonal disorders of the hematopoietic stem cell and comprise a spectrum of more or less well-defined clinical entities: polycythaemia vera, chronic myeloid leukemia, essential thrombocythaemia, and agnogenic myeloid metaplasia. Myelofibrosis, which contributes substantially to the impaired hematopoiesis, is commonly observed in myeloproliferative disorders but it represents the criterion of agnogenic myeloid metaplasia also termed idiopathic myelofibrosis. Although progress has been made in the elucidation of the pathogenesis of myelofibrosis, it still remains unclear.

Transforming growth factor-beta and megakaryocytes in the pathogenesis of idiopathic myelofibrosis.

Although the disease is well described, the pathogenesis of bone marrow fibrosis in idiopathic myelofibrosis still remains unclear. We previously reported elevated intraplatelet transforming growth factor-beta (TGF-beta) levels in patients with this myeloproliferative disorder, compared with healthy subjects. Here, in a series of 16 patients, we show that TGF-beta expression is also increased in patients' peripheral blood mononuclear cells (PBMC): (i) at the mRNA level analysed by Northern blot hybridization and/or reverse transcription-polymerase chain reaction (RT-PCR); (ii) and/or at the secreted peptide level as evaluated in conditioned media from patients' mononuclear cells by a growth inhibition assay on CC164 cells.

Characterization of specific functional receptors for HuIFN-alpha on a human megakaryocytic cell line (Dami): expression related to differentiation.

Interferon-alpha (IFN-alpha) treatment has been shown to be highly effective in inhibiting human megakaryocytopoiesis and controlling thrombocytosis in patients with myeloproliferative disorders. These observations suggest that IFN-alpha might play some role in the biological feature of the megakaryocytic lineage and led us to investigate the presence of specific receptors for IFN-alpha on human megakaryocytic cells, i.e.

Interferon-gamma in vivo reverses the increased platelet levels of platelet-derived growth factor and transforming growth factor-beta in patients with myelofibrosis with myeloid metaplasia.

We previously reported high platelet-derived growth factor (PDGF) and transforming growth factor beta (TGF-beta) levels in platelets from patients with myelofibrosis with myeloid metaplasia. We report here the effects of in vivo administration of recombinant human interferon-gamma on these growth factor levels. Of six patients who entered this study in our institution, four completed the 6-month therapy trial with interferon-gamma PDGF and TGF-beta levels in platelets were evaluated before and after treatment.

Platelet PDGF and TGF-β Levels in Myeloproliferative Disorders.

Myeloproliferative disorders mainly including essential thrombocythemia, polycythemia vera, chronic myeloid leukemia and myelofibrosis with myeloid metaplasia are clonal myeloproliferative diseases in which myelofibrosis is commonly observed. The pathogenesis of myelofibrosis still remains unclear. However it was proposed that an inappropriate release of PDGF from either megakaryocytes in bone marrow or platelets in circulation might promote medullary fibrosis.

Increased intraplatelet levels of platelet-derived growth factor and transforming growth factor-beta in patients with myelofibrosis with myeloid metaplasia.

Platelet-derived growth factor (PDGF) is thought to play some role in the genesis of fibrosis associated with myeloproliferative disorders. In addition, transforming growth factor-beta (TGF-beta) has been confirmed to promote fibrotic process. Both PDGF and TGF-beta have been shown to cooperate with epidermal growth factor (EGF) in regulating the growth of human marrow fibroblasts.

Short- and long-term synergistic effects of human tumor necrosis factor and interferon-gamma on A549 human lung cancer cells maintained in three-dimensional culture.

We have studied the short- and long-term effects of human recombinant tumor necrosis factor (TNF) and TNF/recombinant human interferon-gamma (IFN-gamma) mixtures on A549 human lung carcinoma cells maintained in organotypic culture. Continuous treatments with 2 x 10; 2 x 10(2); 2 x 10(3) and 2 x 10(4) U/ml TNF or with mixtures of TNF/IFN-gamma at 2 x 10(2) and 10(3) U/ml, respectively, were administered. Nodule growth, cell proliferation and cell survival were studied.

Increase of epidermal growth factor receptor expression associated with a lack of antiproliferative effect of IFN-beta in human lung cancer nodules in organotypic culture.

The possible relationship between the effects of alpha 2-, beta- and gamma-interferons (IFNs) on the growth of alveolar II pulmonary tumor cells (A549) maintained in tridimensional organotypic culture (nodules) and the modulation of epidermal growth factor receptor (EGF-R) expression was investigated. Treatment with rHu IFN-alpha 2 or IFN-gamma which results in the inhibition of the growth of A549 nodules had no effect on the binding of 125I-EGF to these cells. In contrast, treatment with rHu IFN-beta which exhibits no antiproliferative activity on A549 nodules resulted in a reproducible increase of the binding of 125I-EGF.

Human lung cancer nodules in organotypic culture: no evidence of correlation between the antiproliferative effects of interferons and the induction of 2',5'-oligoadenylate synthetase.

Alveolar II pulmonary tumor cells (A549), maintained in continuous tridimensional organotypic culture, were used in an attempt to investigate whether there could be a relationship of the 2',5'-oligoadenylate (2,5A) synthetase pathway to the antiproliferative activity of interferons (IFNs) in this particular tumor cell model. IFN-alpha 2, -beta and -gamma were used separately and in combinations. IFN-alpha 2 and -gamma demonstrated an inhibitory effect on the nodule growth, whereas IFN-beta did not.

Potentiation of antiproliferative activity by mixtures of human recombinant IFN-alpha 2 and -gamma on growth of human cancer nodules maintained in continuous organotypic culture.

Alveolar II pulmonary tumor cells (A549 cells) maintained in continuous tridimensional organotypic culture were used to evaluate the eventual potentiation effect of mixtures of recombinant human interferon-alpha 2 and -gamma on growth inhibition of the tumor nodules. A continuous 45 day treatment (interferon renewed three times a week) with 10, 10(2) or 10(3) U/ml of IFN-alpha 2 or -gamma combined with a fixed high dose (10(3) U/ml) of either IFN-alpha 2 or -gamma resulted in an additive or synergistic growth inhibition according to the doses used. There was a close dose-effect relation, the percentage of inhibition increasing proportionally to the variable IFN doses added to the fixed high dose; moreover, the growth inhibition effect occurred earlier with the mixtures than with IFNs used separately.

Modulation of CALLA and HLA-DR on a non T non B leukemic cell line by lipid treatment.

The relationship between membrane lipid fluidity and expression of HLA-DR and cALL (CALLA) antigens was studied in a human non T non B acute lymphoblastic leukemia cell line (Reh). The membrane fluidity was modulated by treatment with cholesteryl hemisuccinate or phospholipids (e.g.

[Ultrastructural peroxidases and immunological markers in acute adult leukaemia: therapeutic applications (author's transl)].

In a retrospective study of 112 adult patients with acute leukaemia (AL), the percentage of undifferentiated leukaemia was reduced to almost 1% by an analysis of routine cytochemical reactions (PAS, peroxidase, esterases and esterase inhibition), B and T lymphocyte markers (IgS, E-rosettes, HuTLA) cAll antigen and ultrastructural detection of peroxidase activity (PO-ME). A simultaneous study of cALL antigen and PO-ME showed reciprocal exclusion of these markers, except in one case of mixed leukaemia. Therapeutically, the value of these tests lies in that patients with typical PAS reaction and cALL antigen consistently respond to vincristine- corticosteroid treatment, whereas patients without cALL and with PO-ME are frequently resistant to that combination of drugs.