Expression of thrombopoietin and its receptor (c-mpl) in chronic myelogenous leukemia: correlation with disease progression and response to therapy

Thrombopoietin from beginning to end

In the two decades since its cloning, thrombopoietin (TPO) has emerged not only as a critical haematopoietic cytokine, but also serves as a great example of bench-to-bedside research. Thrombopoietin, produced by the liver, is the primary regulator of megakaryocyte progenitor expansion and differentiation. Additionally, as TPO is vital for the maintenance of haematopoietic stem cells, it can truly be described as a pan-haematopoietic cytokine. Since recombinant TPO became available, the molecular mechanisms of TPO function have been the subject of extensive research. Via its receptor, c-Mpl (also termed MPL), TPO activates a wide array of downstream signalling pathways, promoting cellular survival and proliferation. Due to its central, non-redundant role in haematopoiesis, alterations of both the hormone and its receptor contribute to human disease; congenital and acquired states of thrombocytosis and thrombocytopenia and aplastic anaemia as a result from dysregulated TPO expression or functional alterations of c-Mpl. With TPO mimetics now in clinical use, the story of this haematopoietic cytokine represents a great success for biomedical research.

Flow cytometric detection of degranulated basophils in chronic myeloid leukemia in accelerated phase

We report a rare case of chronic myeloid leukemia in accelerated phase with basophilic transformation, in which basophils exceeding 70%, were detectable only by flow cytometry because of their morphologic atypicality and degranulation.

Clinical significance of Gata-1, Gata-2, EKLF, and c-MPL expression in acute myeloid leukemia

The aim of this study was to evaluate the biological correlation and prognostic impact of Gata-1, Gata-2, EKLF, and c-MPL transcript level in a group of 41 acute myeloid leukemia (AML) patients. Gata-1 overexpression was related to advanced age and a low percentage of bone marrow blasts and was associated with the expression of CD34 antigen and lymphoid T markers. The negative impact of Gata-1 expression on the probability of achieving complete remission has been confirmed. Gata-2 overexpression was associated with a low percentage of blasts in BM and males. Expression of c-MPL was associated with CD34+ AML and M2 FAB AML subtype. A higher expression of EKLF was found in secondary AML versus primary AML. Nevertheless, patients expressing EKLF had a longer overall survival and event free survival than those patients that did not express EKLF. Our study has identified expression of EKLF as a factor with a favorable impact on prognosis in AML.

BMP4 regulation of human megakaryocytic differentiation is involved in thrombopoietin signaling

Activin A, BMP2, and BMP4, 3 members of the transforming growth factor-beta family, are involved in the regulation of hematopoiesis. Here, we explored the role of these molecules in human megakaryopoiesis using an in vitro serum-free assay. Our results highlight for the first time that, in the absence of thrombopoietin, BMP4 is able to induce CD34(+) progenitor differentiation into megakaryocytes through all stages. Although we have previously shown that activin A and BMP2 are involved in erythropoietic commitment, these molecules have no effect on human megakaryopoietic engagement and differentiation. Using signaling pathway-specific inhibitors, we show that BMP4, like thrombopoietin, exerts its effects on human megakaryopoiesis through the JAK/STAT and mTor pathways. Inhibition of the BMP signaling pathway with blocking antibodies, natural soluble inhibitors (FLRG or follistatin), or soluble BMP receptors reveals that thrombopoietin uses the BMP4 pathway to induce megakaryopoiesis, whereas the inverse is not occurring. Finally, we show that thrombopoietin up-regulates the BMP4 autocrine loop in megakaryocytic progenitors by inducing their production of BMP4 and up-regulating BMP receptor expression. In summary, this work indicates that BMP4 plays an important role in the control of human megakaryopoiesis.

Therapeutic plateletpheresis in a case of symptomatic thrombocytosis in chronic myeloid leukemia

Extreme thrombocytosis is a frequent feature in myeloproliferative disorders which can predispose a person to thrombotic complications. As opposed to other myeloproliferative disorders, symptomatic thrombocytosis is rare in chronic myeloid leukemia. We describe a second case report of chronic myeloid leukemia (Ph chromosome positive) in a patient in chronic phase on hydroxyurea who presented with sudden onset digital cyanosis of the left hand, giddiness, headache and malaise due to extreme thrombocytosis. A 67% global reduction in the platelet count from 1553 x 10(9)/L to 513 x 10(9)/L after two therapeutic plateletpheresis procedures was seen. There was simultaneous improvement in all symptoms except cyanosis on the tip of the middle finger that progressed to dry gangrene. Dramatic reduction in the platelet count and ablation of symptoms by therapeutic plateletpheresis is an effective therapy and should begin as soon as possible.

Significance of myelofibrosis in early chronic-phase, chronic myelogenous leukemia on imatinib mesylate therapy

BACKGROUND

Myelofibrosis is associated historically with a poor prognosis in patients with chronic myelogenous leukemia (CML). Its significance in the recent era of effective therapy with imatinib mesylate is unknown.

METHODS

The current study evaluated the significance of the degree of pretreatment myelofibrosis on response and survival with imatinib therapy in patients with newly diagnosed CML. The study group comprised 198 patients with newly diagnosed Philadelphia chromosome-positive, chronic-phase CML treated with imatinib mesylate therapy. They were analyzed for the prognostic significance of bone marrow reticulin fibrosis.

RESULTS

Severe reticulin (Grade 3-4) fibrosis was observed in 75 patients (38%): Grade 3 in 46 (23%) patients and Grade 4 in 29 (15%) patients. There was a trend towards a lower incidence of a complete cytogenetic response in patients with Grade 4 reticulin fibrosis (76% vs. 89%; P = 0.07), and a significantly worse survival (estimated 3-year survival rate of 87% vs. 97%; P = 0.04).

CONCLUSIONS

Although the prognostic significance of severe reticulin fibrosis in patients with newly diagnosed CML receiving imatinib therapy was better, 15% of patients with Grade 4 reticulin fibrosis still had a worse outcome.

Imatinib mesylate therapy reduces bone marrow fibrosis in patients with chronic myelogenous leukemia

BACKGROUND

Reticulin-stained bone marrow fibrosis is associated with a poor prognosis in patients with chronic myelogenous leukemia (CML). Resolution of fibrosis with therapy may improve patient outcome.

METHODS

The effect of imatinib therapy on bone marrow fibrosis was evaluated in 40 patients with chronic-phase CML who were treated after interferon-alpha failure.

RESULTS

Thirty-one patients (78%) had severe (Grade 3 or 4) reticulin fibrosis prior to therapy. After imatinib therapy was administered for 3 to > 24 months, fibrosis was reduced by at least 2 grades in 19 of the 31 patients (61%) and by at least 1 grade in 34 patients (85%). There was no correlation noted between reduction of fibrosis and cytogenetic response. However, a reduction in fibrosis was found to correlate with a reduction in bone marrow megakaryocytosis (P = 0.002).

CONCLUSIONS

Treatment with imatinib mesylate appears to reduce CML-associated bone marrow fibrosis in most patients who are treated during the chronic phase of disease. This effect may be independent of the degree of suppression of Philadelphia chromosome-positive cells, and may improve prognosis in patients with CML.