Hypersensitivity of circulating progenitor cells to megakaryocyte growth and development factor (PEG-rHu MGDF) in essential thrombocythemia

Abstract

Hematopoietic progenitor cells in 2 myeloproliferative disorders, juvenile chronic myelomonocytic leukemia and polycythemia vera, are known to be hypersensitive to cytokines that control normal progenitor cell proliferation, differentiation, and survival in their respective granulocyte/macrophage and erythroid lineages. Because thrombopoietin controls these functions in the normal megakaryocytic lineage, we asked the question: Are megakaryocytic progenitor cells in the myeloproliferative disorder essential thrombocythemia (ET) hypersensitive to thrombopoietin? Peripheral blood mononuclear cells from patients with ET, or secondary (reactive) thrombocytosis (2°T), or healthy volunteers were grown in strictly serum-free agarose culture containing interleukin 3 (IL-3) and all-trans-retinoic acid, with various concentrations of PEG-rHu megakaryocyte growth and development factor (MGDF). The concentration of cytokine at half-maximum colony number served as a measure of progenitor cell sensitivity. Hypersensitivity to PEG-rHu MGDF was found in circulating progenitors from 18 of 20 (90%) informative patients with presumptive diagnosis ET, 1 of 8 (12.5%) 2 °T patients, and none of the 22 healthy volunteers. Median MGDF sensitivity ratio in ET patients was approximately 53 times greater than in the controls. This hypersensitivity, which was also directed to rHu thrombopoietin, was highly specific with respect to cytokine, disease, and cell lineage. We propose that, despite their single pluripotential cell origin, the different clinicopathologic phenotypes in different chronic myeloproliferative disorders are determined by lineage-restricted hypersensitivities of hematopoietic progenitor cells to endogenous cytokines. This work emphasizes the importance of stringent serum-free conditions for revealing true sensitivities to cytokines. The findings also offer a basis for evolving a positive test for ET, a diagnosis now made essentially by exclusion.

The 2001 World Health Organization and Updated European Clinical and Pathological Criteria for the Diagnosis, Classification, and Staging of the Philadelphia Chromosome-Negative Chronic Myeloproliferative Disorders

“…9 was found for SCF, a cytokine active in several different cell lineages. 59 These results clearly indicate that the various clinicopathological phenotypes of the clonal MPDs (ET, PV, and IMF) are related to (and perhaps determined by) specific hypersensitivities of their progenitor cells to normal endogenous cytokine: EEC-IGF-1 hypersensitivity for PV, TPO hypersensitivity for thrombocythemia (ET and early PV mimicking ET), and GM-CSF and SCF hypersensitivity for granulocytosis in PV and for CIMF, respectively (Table 1; Fig. 5).…”

“…Spontaneous endogenous megakaryocyte colony formation (EMC or colony-forming unit [CFU] -megakaryocyte) in the absence of exogenous growth factors has been described in ET patients. [55][56][57][58][59][60] Their median TPO sensitivity ratios were more than 50 times higher than normal and this was highly specific with respect to cytokine, disease, and cell lineage, suggesting a lineage-restricted hypersensitivity of hematopoietic progenitors to normal endogenous TPO in thrombocythemia. 59 In patients with IMF, clear evidence of hypersensitivity 9 The course of polycythemia vera (PV) is usually a matter of years and myelofibrosis with progressive splenomegaly may develop in about one fourth of patients after 10 to 20 years of follow-up.…”

“…5). [47][48][49][50][59][60][61] PRV-1 gene expression has been detected in nearly all PV and in about half of the ET patients, who also demonstrated spontaneous EEC, and there was a nearly 100% concordance between EEC and PRV-1 positivity in PV and ET patients as well as EEC negativity and normal PRV-1 expression in ET patients. [48][49][50][51][52][53] The EEC/PRV-1/JAK2 V617F positive disease may present clinically as an ET (early PV mimicking ET) that will develop into PV, as classical PV, or as a variant of CIMF that has quickly passed the hypercellular polycythemic stage (Table 1).…”

A Gain-of-Function Mutation ofJAK2in Myeloproliferative Disorders

“…Hypersensitivity to insulin-like growth factor, thrombopoietin, interleukin-3, and other cytokines has been described in hematopoietic progenitor cells from patients with myeloproliferative disorders. 39,[41][42][43] How the V617F mutation sustains the increased phosphorylation of JAK2 in the presence of serum, but in the absence of interleukin-3, and the factor or factors in serum that mediate this effect remain unknown. Nevertheless, the functional relevance of the V617F mutation is supported by the finding that endogenous erythroid colonies were present in 89 percent of patients with V617F and the close association between homozygosity for the V617F mutation and 9pLOH, which demonstrates the survival advantage of such homozygous hematopoietic cells.…”

A family with hereditary thrombocythaemia and normal genes for thrombopoietin and c‐Mpl

“…The inappropriately elevated levels of plasma free TPO encountered in ET are due, at least in part, to either a clonal defect in platelet/megakaryocyte expression or downregulation of TPO‐cMpl causing impaired binding and clearance of TPO (Horikawa et al , 1997; Teofili et al , 2002). Despite the reduced binding of TPO to megakaryocytes in ET, these progenitors are also markedly hypersensitive to the action of the hormone, leading to increased megakaryocytopoiesis and platelet production (Axelrad et al , 2000). Similarly to ET, increased TPO levels were reported in patients with HT and TPO mutations (Kondo et al , 1998; Wiestner et al , 1998; Ghilardi et al , 1999).…”