A recent study in dogs suggested that erythropoietin (EPO) not only promotes the synthesis of increased numbers of reticulated platelets but that these newly produced platelets are hyperreactive compared with controls. Because of the increasing use of EPO in the perioperative setting, we characterized the effects of EPO on platelet reactivity in healthy human volunteers. In a randomized, controlled trial, we studied the effects of EPO on platelet reactivity, thrombopoiesis, and endothelial activation in circumstances similar to those of autologous blood donation. Thirty healthy male volunteers received placebo or EPO (100 or 500 U/kg of body weight given intravenously) three times a week for 2 weeks and underwent phlebotomy on days 8 and 15. Thrombin receptor–activating peptide induced expression of P-selectin, and CD63 increased 2- to 3-fold during EPO treatment. The enhanced platelet reactivity was also reflected by a 50% increase in soluble P-selectin in plasma. Plasma E-selectin levels increased in a dose-dependent fashion by more than 100% during EPO treatment, indicating substantial activation of endothelial cells. A 10% to 20% increase in platelet counts was observed in both EPO groups on day 5. In the placebo group, platelets increased only several days after the first phlebotomy. The increase in platelet counts was not reflected by changes in the amounts of reticulated platelets or circulating progenitor cells. In summary, we found that EPO markedly enhances endothelial activation and platelet reactivity, which may adversely affect patients at cardiovascular risk. However, the increased platelet reactivity could be exploited in patients with platelet dysfunction.

Autonomous release of hematopoietic growth factors may play a crucial role in the pathogenesis of certain hematological malignancies. Because of its cytokine synthesis-inhibiting action, interleukin 10 (IL-10) could be a potentially useful molecule to affect leukemic cell growth in such disorders. Chronic myelomonocytic leukemia (CMML) cells spontaneously form myeloid colonies (colony-forming units-granulocyte/macrophage) in methylcellulose, suggesting an autocrine growth factor-mediated mechanism. We studied the effect of recombinant human IL-10 (rhIL-10) on the in vitro growth of mononuclear cells obtained from peripheral blood or bone marrow of patients with CMML. IL-10 specifically binding to leukemic cells had a profound and dose-dependent inhibitory effect on autonomous in vitro growth of CMML cells. IL-10 significantly inhibited the spontaneous growth of myeloid colonies in methylcellulose in 10/11 patients, and autonomous CMML cell growth in suspension in 5/5 patients tested. Spontaneous colony growth from CMML cells was also markedly reduced by addition of antigranulocyte/macrophage colony-stimulating factor (GM-CSF) antibodies, but not by addition of antibodies against G-CSF, IL-3, or IL-6, IL-10-induced suppression of CMML cell growth was reversed by the addition of exogenous GM-CSF and correlated with a substantial decrease in GM-CSF production by leukemic cells, both at the mRNA and protein levels. Our data indicate that IL-10 profoundly inhibits the autonomous growth of CMML cells in vitro most likely through suppression of endogenous GM-CSF release. This observation suggests therapeutic evaluation of rhIL-10 in patients with CMML.

IL-10 is effective in reversing in vitro hematopoietic suppression by PBMNC from AA patients. These results suggest therapeutic evaluation of rhIL-10 in patients with AA.

We have originally shown that spontaneous granulocyte/macrophage colony (CFU-GM) formation in semisolid medium is a characteristic in vitro feature of chronic myelomonocytic leukemia (CMML). However, the clinical significance of spontaneous CFU-GM growth in CMML is unknown so far. CFU-GM growth characteristics were studied in semisolid cultures in the absence of exogenous cytokines using peripheral blood mononuclear cells in 30 patients with CMML at first presentation. The median number of CFU-GM/10(5) MNC of all patients was 48.5 (range 0-622) with 18 patients having colony numbers below 100 (low CFU-GM growth) and 12 patients above 100 (high CFU-GM growth). Kaplan-Meier analysis revealed that patients with high CFU-GM growth had a significantly shorter survival than patients with low CFU-GM growth (median 6.5 vs. 44.5 months, p<0.00002). The probability of survival after 2 years was 60.5% for patients with low colony growth but 0% in those with high colony formation. Patients with CFU-GM >100 had a significantly higher WBC count, a higher LDH, and a higher number of blast cells in blood and bone marrow than patients with low colony growth. Moreover, patients with high colony growth had more often splenomegaly and lower platelet counts. In seven patients, in whom semisolid in vitro cultures were performed after transformation into RAEBT/AML, spontaneous colony growth was significantly increased as compared to CFU-GM growth in patients before transformation (median number/10(5) MNC 533, range 212-4553, p<0.005). This study demonstrates that high (>100) spontaneous CFU-GM formation in CMML at presentation correlates with increased disease activity and represents a novel and important prognostic factor predicting for short survival of CMML patients.

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.