Effect of adherent cells on the regulation of BFU-E in patients with myeloproliferative disease

T cells from patients with polycythemia vera elaborate growth factors which contribute to endogenous erythroid and megakaryocyte colony formation

In the present study, we report that media conditioned by polycythemia vera (PV) CD3+ cells promote BFU-E and CFU-Mk colony formation by both cord blood and PV peripheral blood CD34+ cells in the absence of exogenous cytokines and promoting megakaryocyte proplatelet formation. CD3+ cells constitutively produce elevated levels of IL-11, while stimulation with the addition of phytohemagglutinin (PHA) increased GM-CSF levels in most of the patients with PV. Anti-IL-11-neutralizing antibody partially inhibited the formation of BFU-E and CFU-Mk colonies promoted by PV CD3+ cell-conditioned media. Although IL-11 is not produced by normal T cells, real-time PCR and flow cytometric analysis showed that IL-11 was upregulated in the CD3+ cells of most PV patients as compared to normal CD3+ cells. In addition, a greater percentage of BFU-E colonies formed by PV CD34+ cells in the presence of PV CD3+ cell-conditioned media alone were JAK2V617F-positive as compared with that induced by EPO. We conclude that dysregulated production of soluble growth factor(s), including IL-11 and GM-CSF by PV T cells, contributes to the in vitro formation of erythroid colonies in the absence of exogenous cytokines by PV CD34+ cells and likely plays a role in sustaining hematopoiesis in PV.

A simplified endogenous erythroid colony assay for the investigation of polycythaemia

The in vitro growth of erythroid colonies in the absence of erythropoietin, known as endogenous erythroid colonies (EEC) forms part of the diagnostic criteria for polycythaemia vera (PV). The availability of EEC culture in routine laboratory setting is limited as culture methods are technically demanding, difficult to standardize, expensive and laborious. In this study, we assessed the performance characteristics of a simplified method using ammonium chloride red cell lysis followed by culture on commercially available, batch-tested, methylcellulose media. Seventy-six patients were included; four were secondarily excluded on the basis of culture failure. Of the 14 patients with PV, 13 (93%) were positive for EEC on at least one occasion: 90% (nine of 10) of bone marrow and 67% (six of nine) of peripheral blood specimens were positive. All 30 patients with secondary polycythaemia (n = 12) or apparent polycythaemia (n = 18) were negative for EEC. The incidence of EEC in idiopathic erythrocytosis was 40% (eight of 28); 50% (five of 10) in those who met one of the minor criteria for PV and 17% (three of 18) in those who did not. We conclude that our EEC assay yield results comparable with that of more elaborate methods.

The predictive value of clonogenic stem cell assays for the diagnosis of polycythaemia vera

Spontaneous growth of erythroid progenitor cells is one of the hallmarks of polycythaemia vera (PV). In vitro clonogenic assays can be used to support the diagnosis of PV. However, clonogenic assays are difficult to standardize, and their diagnostic value is accepted as a minor criteria for PV only in the case of positive results. Clonogenic assays need to be validated and normal ranges established carefully before they can be used for diagnostic purposes. In a retrospective study, we analysed the results of 146 consecutive clonogenic assays performed in patients with erythrocytosis between January 1992 and December 2000. Normal ranges were established on the basis of the results from 81 controls. The charts of the 146 patients were reviewed and the patients were allocated to the following diagnostic groups: PV (n = 38) and non-primary erythrocytosis (NPE, n = 65) according to the criteria of Pearson & Messinezy. In total, 43 patients were excluded from the study because of missing data. The clonogenic assay results were correlated with the final clinical diagnosis of the patients. At a cut-off value of 5 erythroid colony-forming unit colonies per well, 29 out of 38 patients with PV showed positive results, and 9 out of 38 patients showed false-negative results. In the NPE group, there were 64 out of 65 real-negative results and 1 out of 65 false-positive result. Thus the positive predictive value of the clonogenic assay for the diagnosis of PV was 97%. We conclude that clonogenic assays, in the case of positive results, and if carefully validated, are very useful and reliable tools for the diagnosis of PV.

Interleukin-10 Inhibits Erythropoietin-Independent Growth of Erythroid Bursts in Patients With Polycythemia Vera

In polycythemia vera (PV) erythroid colonies that grow in vitro in the absence of exogenous erythropoietin (EPO) arise from the abnormal clone that is responsible for overproduction of red blood cells. Although the mechanism of autonomous formation of burst-forming units-erythroid (BFU-E) is not fully understood, a spontaneous release of growth regulatory molecules by PV cells and/or by accessory cells is likely to be involved. Because of its cytokine synthesis inhibiting action, interleukin-10 (IL-10) could be a potentially useful molecule to modulate abnormal erythropoiesis in PV. We studied the effect of recombinant human IL-10 on the EPO-independent growth of erythroid bursts derived from peripheral blood mononuclear cells (PBMNCs) of patients with PV. IL-10 showed a profound, dose-dependent, and specific inhibitory effect on autonomous BFU-E formation. Ten nanograms per milliliter of IL-10 significantly suppressed spontaneous growth of erythroid colonies in methylcellulose in five of five PV patients tested with a mean inhibition by 81% (range, 72-94). To elucidate the possible mechanism of the inhibitory action of IL-10 we further studied the effect of anticytokine antibodies on autonomous BFU-E growth and the ability of exogenous cytokines to restore IL-10–induced suppression of erythroid colony growth. Among a panel of growth regulatory factors tested (granulocyte-macrophage colony-stimulating factor [GM-CSF], IL-3, granulocyte colony-stimulating factor, stem cell factor, and insulin-like growth factor-1) GM-CSF was the only molecule for which both an inhibition of spontaneous BFU-E formation by its respective antibody as well as a significant restimulation of erythroid colonies in IL-10-treated cultures by exogenous addition was found. Moreover, inhibition of GM-CSF production by IL-10 was shown in PV PBMNCs at the mRNA level. Our data indicate that autonomous BFU-E growth in PV can be profoundly inhibited by IL-10 and that this inhibitory effect seems to be at least in part secondary to suppression of endogenous GM-CSF production.

© 1998 by The American Society of Hematology.

Interleukin-10 Inhibits Erythropoietin-Independent Growth of Erythroid Bursts in Patients With Polycythemia Vera

In polycythemia vera (PV) erythroid colonies that grow in vitro in the absence of exogenous erythropoietin (EPO) arise from the abnormal clone that is responsible for overproduction of red blood cells. Although the mechanism of autonomous formation of burst-forming units-erythroid (BFU-E) is not fully understood, a spontaneous release of growth regulatory molecules by PV cells and/or by accessory cells is likely to be involved. Because of its cytokine synthesis inhibiting action, interleukin-10 (IL-10) could be a potentially useful molecule to modulate abnormal erythropoiesis in PV. We studied the effect of recombinant human IL-10 on the EPO-independent growth of erythroid bursts derived from peripheral blood mononuclear cells (PBMNCs) of patients with PV. IL-10 showed a profound, dose-dependent, and specific inhibitory effect on autonomous BFU-E formation. Ten nanograms per milliliter of IL-10 significantly suppressed spontaneous growth of erythroid colonies in methylcellulose in five of five PV patients tested with a mean inhibition by 81% (range, 72-94). To elucidate the possible mechanism of the inhibitory action of IL-10 we further studied the effect of anticytokine antibodies on autonomous BFU-E growth and the ability of exogenous cytokines to restore IL-10–induced suppression of erythroid colony growth. Among a panel of growth regulatory factors tested (granulocyte-macrophage colony-stimulating factor [GM-CSF], IL-3, granulocyte colony-stimulating factor, stem cell factor, and insulin-like growth factor-1) GM-CSF was the only molecule for which both an inhibition of spontaneous BFU-E formation by its respective antibody as well as a significant restimulation of erythroid colonies in IL-10-treated cultures by exogenous addition was found. Moreover, inhibition of GM-CSF production by IL-10 was shown in PV PBMNCs at the mRNA level. Our data indicate that autonomous BFU-E growth in PV can be profoundly inhibited by IL-10 and that this inhibitory effect seems to be at least in part secondary to suppression of endogenous GM-CSF production.

© 1998 by The American Society of Hematology.

In vitro culture growth of erythroid progenitors and serum erythropoietin assay in the differential diagnosis of polycythaemia

BACKGROUND

We assessed the in vitro culture growth of erythroid progenitors [burst forming unit-erythroid (BFU-E)] and serum erythropoietin (EPO) levels in different groups of polycythaemia to determine the discriminative power in differential diagnosis of polycythaemia.

METHODS

We used the methylcellulose culture technique to study the growth of endogenous erythroid colonies (EECs) and EPO-dependent BFU-E from bone marrow (BM) and/or peripheral blood (PB) cells from 40 patients with polycythaemia vera (PV), 13 with secondary polycythaemia (SP), 19 with pure erythrocytosis (PE), five with PE and PV evolution later (PE-PV), and 12 with relative polycythaemia (RP). The serum EPO levels were measured by radioimmunoassay before treatment in 47 patients, 23 SP patients, 19 PE patients, five PE-PV patients and 16 RP patients, as well as after treatment in 38 PV patients, five PE-PV patients and 12 PE patients.

RESULTS

The results of the erythroid progenitor culture assay showed that the numbers of EPO-dependent BFU-E in BM did not differ significantly among groups. The PB BFU-E were significantly higher in PV than in SP or PE, and no statistical difference were found among patients with SP, PE and RP. There was a correlation between BM BFU-E and PB BFU-E in the individual PV and PE patients. EECs were present in all BM and PB cultures of untreated and phlebotomy-treated PV and PE-PV patients, but were absent in 6 of 17 PV patients who had received cytotoxic therapy. EECs were not found in SP, PE and RP. PB could substitute for BM in the EEC or the BFU-E assay. Both pretreatment and post-treatment serum EPO levels of PV and PE-PV were similar, which were significantly lower than SP, PE or RP. The serum EPO levels in treated PV or PE-PV patients who had normal haematocrit values were not significantly different from those in untreated patients. In contrast, the phlebotomy-treated PE patients had significantly higher serum EPO values than untreated PE patients. In the differentiation between PV and PE, the sensitivity, specificity, positive predictive value and negative predictive value of post-treatment serum EPO levels at a cut-off level of < or = 9 UL-1 were 74%, 92% and 52% respectively. The discriminative power of post-phlebotomy serum EPO levels was even higher with a positive predictive value of 80% and negative predictive value of 92% for the prediction of PV evolution in patients with pure erythrocytosis of unknown origin.

CONCLUSION

The present study showed that apart from EEC assay, the post-phlebotomy serum EPO level was a sensitive and specific parameter in the differential diagnosis of polycythaemia, in particular for the identification of PV among patients with unclassifiable polycythaemia.

Pathogenesis of polycythaemia vera

Polycythaemia vera (PV) is thought to result from clonal expansion of a transformed multipotent stem cell. Progenitors from patients with PV display abnormal responses to several growth factors, suggesting the presence of a defect in a signalling pathway common to different growth factors. A number of approaches are now focused on defining the molecular lesion or lesions. Identification of causal genes will be of considerable interest both to clinicians, who currently lack a specific and sensitive diagnostic test, and to scientists interested in fundamental issues of stem cell behaviour.

The effects of IL-1 and IL-4 on the Epo-independent erythroid progenitor in polycythaemia vera

Human recombinant interleukin-1 (IL-1) was studied for its effects on the erythroid progenitors from normal subjects and from patients with polycythaemia vera (PV). No supportive effect of IL-1 was noticed on the normal, erythropoietin (Epo) dependent, erythroid burst-forming unit (BFU-E) using peripheral blood or bone marrow. In contrast, the Epo-independent BFU-E from peripheral blood of PV patients could be stimulated significantly. This enhancing effect of IL-1 was not only observed with unsorted but also with sorted CD34+ cells. In addition, it was shown that IL-1 indirectly stimulated the Epo-independent BFU-E because anti-GM-CSF could abrogate the supportive effects of IL-1. In contrast to the Epo-independent BFU-E, the Epo-dependent erythroid colony formation from PV patients could not be augmented by IL-1. Finally, we studied the effects of IL-4 on the Epo-independent BFU-E, because IL-4 can affect the erythroid colony formation and modulate the effects of IL-1. IL-4 suppressed the Epo-independent BFU-E. This effect could be counteracted by the addition of IL-1 to the culture medium. However, the suppressive effect of IL-4 was not related to a decline in spontaneous release of IL-1, because an anti-IL-1 antibody did not modify the spontaneous erythroid colony formation. These data indicate that IL-1 and IL-4 exert separate influences on the Epo-independent erythroid colony formation in PV.

The in vitro effects of interferon-gamma, interferon-alpha, and tumour-necrosis factor-alpha on erythroid burst-forming unit growth in patients with non-leukaemic myeloproliferative disorders

We have studied the effects of interferons gamma (IFN-gamma) and alpha (IFN-alpha), and tumour-necrosis factor-alpha (TNF) on circulating 14-day erythroid progenitor cell (BFU-E) growth in vitro from patients with non-leukaemic myeloproliferative disorders (MPD) compared with normal controls. IFN-gamma (1000 U/ml) inhibited BFU-E growth in all controls studied (mean growth +/- SE = 61% +/- 6%, n = 10). In 7 of 11 MPD studied there was no inhibition, and in some cases clear enhancement of BFU-E growth by IFN-gamma. When cultured in the presence of recombinant erythropoietin (rEpo) 1 U/ml, both IFN-alpha and TNF (at 100 and 1000 U/ml) produced a similar degree of inhibition of BFU-E growth in MPD and controls. The inhibition by 100 U/ml IFN-alpha was abrogated, partially in controls but completely in MPD, by increasing the dose of rEpo to 5 U/ml. Similarly, the increase in rEpo dose enhanced BFU-E growth in cultures with 100 U/ml TNF, but had little effect on cultures containing 1000 U/ml of either IFN-alpha or TNF. The aberrant in vitro response to IFN-gamma demonstrated in some of these patients may be of relevance to the pathophysiology of MPD. These results fail to demonstrate a differential in vitro effect for IFN-alpha on MPD BFU-E growth compared with controls and suggest that the in vitro suppression of haemopoiesis by IFN-alpha when used in MPD treatment is non-specific.

In vitro growth of erythroid progenitor cells (BFU-E) and production of burst-promoting activity (BPA) by T lymphocytes in patients with myelodysplastic syndromes

The in vitro growth of circulating erythroid progenitors (BFU-E) populations and the production of burst-promoting activity (BPA) by T lymphocytes have been studied in 17 patients with myelodysplastic syndromes. Based on the in vitro growth patterns of BFU-E, four groups of patients have been identified: i) normal BFU-E growth; ii) low spontaneous BFU-E growth, but normal response to LCM; iii) impaired BFU-E response to LCM; iv) no BFU-E growth. The pattern of BFU-E growth seems to be related to the clinical stage of the disease rather than to the FAB subgroup to which the patients belong. The ability of T lymphocytes to stimulate BFU-E growth was significantly reduced in all patients. The possible mechanisms inducing the impaired production of BPA by T lymphocytes are discussed. The in vitro evaluation of circulating erythroid precursors can supply useful prognostic information and possibly indications concerning the responsiveness of erythropoietic stem cells to recombinant human erythropoietin in vivo.