Effects of human FLT3 ligand on myeloid leukemia cell growth: heterogeneity in response and synergy with other hematopoietic growth factors

A novel hematopoietic growth factor for primitive hematopoietic progenitor cells, the ligand for the flt3/flk2 receptor, (FL), has been recently purified and its gene has been cloned. In the present study, we investigated the effects of FL on the proliferation and differentiation of normal and leukemic myeloid progenitor cells. We demonstrate that FL is a potent stimulator of the in vitro growth of granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), or G-CSF-dependent granulocyte-macrophage committed precursors from Lin- CD34+ bone marrow cells of normal donors. By contrast, FL does not affect the growth of erythroid-committed progenitors even in the presence of erythropoietin. The effect of FL on the proliferation and on the in vitro growth of clonogenic leukemic precursor cells was studied in 54 acute myeloid leukemia (AML) cases. Fresh leukemia blasts from 36 of 45 patients with AML significantly responded to FL without any relation to the French-American-British (FAB) subtype. FL stimulated the proliferation of leukemic blasts in a dose-dependent fashion. Synergistic activities were seen when FL was combined with G-CSF, GM-CSF, IL-3, or stem cell factor (SCF). FL as a single factor induced or increased significantly colony formation by clonogenic precursor cells from 21 of 24 patients with AML. In the presence of suboptimal and optimal concentrations of G-CSF, GM-CSF, IL3, SCF, or a combination of all factors, FL strongly enhanced the number of leukemic colonies (up to 18-fold). We also evaluated the induction of tyrosine phosphorylated protein on FL stimulation in fresh AML cells. We demonstrate that, on FL stimulation, a band of phosphorylated protein(s) of about 90 kD can be detected in FL-responsive, but not in FL-unresponsive cases. This study suggests that FL may be an important factor for the growth of myeloid leukemia cells, either as a direct stimulus or as a synergistic factor with other cytokines.

Transcriptional and post-transcriptional regulation of granulocyte-macrophage colony-stimulating factor production in human growth factor dependent M-07e cells

To elucidate the regulatory mechanisms of granulocyte-macrophage colony-stimulating factor (GM-CSF) production in human myeloid leukaemic cells we studied GM-CSF gene transcription, mRNA expression and GM-CSF secretion in human growth factor dependent M-07e cells. GM-CSF transcript was detected in cells cultured in the presence of interleukin-3 (IL-3). GM-CSF or mast cell growth factor (MGF), whereas it was undetectable in growth factor deprived cells. Growth factor re-addition induced, within 2 h, the appearance of GM-CSF mRNA. Nuclear run-on experiments demonstrated that the increase of GM-CSF mRNA levels depends on GM-CSF gene transcription. The simultaneous addition, to deprived cells, of the growth factor, and of cycloheximide (CHX) for 2 h inhibited GM-CSF mRNA expression, suggesting the requirement for newly made proteins for GM-CSF gene transcription. By means of the M-07e bioassay, which allows the detection of GM-CSF, IL-3 and MGF activities, and neutralizing antibodies to each of these factors, GM-CSF activity was detected in the cell-free extract of both IL-3- and MGF-sustained cells and of cells deprived for 24 h. This finding demonstrates that M-07e cells produce and store biologically active GM-CSF in response to both IL-3 and MGF. In contrast, analysis of the growth stimulatory activity present in the culture supernatants revealed that MGF, unlike IL-3, is able to induce the secretion of consistent amounts of GM-CSF. Taken together, our results suggest that, in M-07e cells, GM-CSF gene transcription and GM-CSF production are mediated, unlike its secretion, by mechanisms shared by IL-3 and MGF.

Overexpression of Shc proteins potentiates the proliferative response to the granulocyte-macrophage colony-stimulating factor and recruitment of Grb2/SoS and Grb2/p140 complexes to the beta receptor subunit

The high affinity receptor for GM-CSF consists of a unique alpha subunit and a beta subunit that is shared with receptors for IL-3 and IL-5. Activation of GM-CSF receptor (GMR) triggers two distinct cytoplasmic signalling pathways, JAK2 and Ras, and is sufficient to maintain proliferation of growth factor-dependent cell lines. Shc proteins are phosphorylated upon activation of GMR and may be involved in the transmission of GM-CSF signals to Ras. To define the role of Shc proteins in cells stimulated with GM-CSF, we investigated both the network of interactions that involve Shc after GM-CSF stimulation and the effects of overexpressing Shc proteins on the proliferative response to GM-CSF. Two cytoplasmic complexes, Grb2/Sos and Grb2/p140 bind through the Grb2 SH2 domain to phosphorylated Shc, and are thereby recruited to the beta subunit. Both complexes are stable, even in the absence of ligand, and depend on the direct association of p140 and Sos respectively with the SH3 domains of Grb2. p140 is an uncharacterized protein constitutively phosphorylated on tyrosine and, in its Grb2-bound form, expressed only in hematopoietic cells, the oligomeric complex formed by phosphorylated beta subunit-phosphorylated Shc-Grb2-SoS-p140 is also induced by IL-3 and L-5 stimulation of growth-factor dependent cell lines. Overexpression of wild-type Shc proteins in growth factor-dependent cells increases both MAP kinase activation and proliferation in response to GM-CSF. These effects require the association of Shc with Grb2. Taken together these results indicate that phosphorylation of Shc proteins is a crucial step in the transmission of GM-CSF proliferative stimuli, since it creates a high affinity binding site for the Grb2/SoS complex, whose function is to activate Ras and, for the Grb2/p140 complex, whose function remains unknown.

Convergence of signaling by interleukin-3, granulocyte-macrophage colony-stimulating factor, and mast cell growth factor on JAK2 tyrosine kinase

Mast cell growth factor (MGF) (also called stem cell factor) synergizes with several lymphokines, including interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF), to promote proliferation and differentiation of certain hemopoietic progenitor cells. Although similar patterns of tyrosine-phosphorylated proteins characterize cells stimulated by MGF, IL-3, and GM-CSF, only the MGF receptor is a tyrosine kinase, and the heterodimeric receptors for IL-3 and GM-CSF share a common beta subunit that is devoid of enzymatic activity. Here we show that signaling pathways utilized by all three cytokines include the cytoplasmic tyrosine kinase JAK2. Analysis of several factor-dependent myeloid cell lines indicated that JAK2 is physically associated with the common beta subunit and with MGF receptor (c-Kit) even prior to ligand binding. However, each of the ligands induced elevated tyrosine phosphorylation of JAK2 and a consequent increase in its catalytic activity. These results demonstrate for the first time the convergence within the same myeloid cells of signaling pathways originating in two distinct lymphokine receptors and a tyrosine kinase receptor on activation of a cytoplasmic tyrosine kinase.

Effect of two different therapeutic approaches on total and cardiovascular mortality in a Cardiovascular Study in the Elderly (CASTEL)

Although limited numbers of elderly subjects have occasionally been included in population-based studies, only a few studies have been conducted specifically on elderly hypertensives, and practically none at a population level. We studied 655 hypertensive subjects from a cohort of 2,254 elderly subjects. The intervention consisted of the creation of a Hypertension Outpatients' Clinic under our auspices but with complete co-operation from general practitioners, randomizing the identified hypertensive patients into pre-established therapeutic drug regimens, and early follow-up recording of mortality for 7 years. The drugs used were clonidine (n = 61), nifedipine (n = 146) and the fixed combination of atenolol+chlorthalidone (n = 144); 304 subjects underwent "free therapy" by their personal physicians without any special intervention. There were 1,404 normotensive subjects. Overall 7-year follow-up mortality was 34.9% in the hypertensive subjects receiving "free therapy", 22.5% in those receiving "special care", and 24.2% in the normotensives. Cardiovascular mortality was respectively 23.7%, 12.2%, and 12.0%. Overall and cardiovascular annual cumulative mortality were significantly lower in the << special therapy >> than in the << free therapy >> group. The fixed combination of atenolol and chlorthalidone reduced mortality below that of the normotensives, independent of other cardiovascular risk factors.

Protein kinase C-dependent release of a functional whole extracellular domain of the mast cell growth factor (MGF) receptor by MGF-dependent human myeloid cells

The mast cell growth factor (MGF) affects migration, proliferation and differentiation of erythroid and myeloid progenitor cells by binding to a transmembrane receptor tyrosine kinase encoded by the c-Kit proto-oncogene. By using MGF-dependent human myeloid cell lines (M-07e and TF-1), here we show that a Kit-related 100 kDa protein is associated with the cell but it undergoes release into the medium upon treatment with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of protein kinase C. Immunological analysis with a series of antibodies to Kit indicated that the released protein (p100Kit) contains the whole glycosylated extracellular portion of the transmembrane Kit protein (p145Kit). The secreted protein retained the ability to specifically bind MGF. Moreover, p100Kit was able to block the mitogenic effect of MGF on cultured M-07e cells, suggesting that the soluble protein may function as a physiological antagonist of MGF.

Regulation of c-kit expression in human myeloid cells

In both murine and human systems the c-kit ligand, also known as mast cell growth factor (MGF), acts synergistically with several colony stimulating factors, including the granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin 3 (IL-3), in stimulating the proliferation and differentiation of different types of hematopoietic progenitors. In addition, MGF is also known to enhance the effects of GM-CSF and IL-3 on the in vitro proliferative activity of myeloid leukemic cells. MGF synergizes with a number of other cytokines such as GM-CSF, IL-3, IL-2, IL-4, IL-6 and IL-9 in sustaining the proliferation of growth factor dependent M-07e cells. In order to explore the molecular basis of this synergistic activity and to elucidate the regulatory mechanisms of c-kit expression, we investigated the effects of GM-CSF, IL-3 and MGF on c-kit mRNA and protein levels in M-07e cells. GM-CSF, unlike MGF and IL-3, induced a transient but significant increase of c-kit mRNA levels. Moreover, following MGF and GM-CSF treatment, c-kit protein expression in M-07e cells decreased, whereas all the other cytokines tested are unable to modulate c-kit protein. These data together with the results of protein turnover analysis suggest that MGF and GM-CSF regulate c-kit expression at the post-transcriptional level. In addition, the finding that IL-3 has no detectable effect on c-kit expression raises the possibility that GM-CSF-induced c-kit regulation is not mediated by the common signal transducing element: the beta subunit of the IL-3/GM-CSF receptor complex.

Interleukin 3 stimulates proliferation and triggers endothelial-leukocyte adhesion molecule 1 gene activation of human endothelial cells

Proliferation and functional activation of endothelial cells within a tissue site of inflammation are regulated by humoral factors released by cells, such as T lymphocytes and monocytes, infiltrating the perivascular space. In the present study we investigated the effects of interleukin 3 (IL-3), an activated T lymphocyte-derived cytokine, on cultured human umbilical vein endothelial cells (HUVEC). Proliferative activity, evaluated both by estimation of the fraction of cells in the S phase and by direct cell count demonstrated that IL-3, at the dose of 25 ng/ml, enhances more than threefold both DNA synthesis and cell proliferation above baseline control conditions. Binding studies with radioiodinated ligand demonstrated that HUVEC constitutively express a smaller number of IL-3 binding sites (approximately 99 binding sites per cell, with an apparent Kd of 149 pM). Accordingly, molecular analysis showed the presence of transcripts for both alpha and beta subunits of the IL-3 receptor. Functional activation of endothelial cells was evaluated by the expression of the endothelial-leukocyte adhesion molecule 1 (ELAM-1) transcript and by leukocyte adhesion. The ELAM-1 gene transcript was clearly detectable 4 h after IL-3 addition and started to decrease after 12 h. Moreover, IL-3-induced ELAM-1 transcription was followed by enhanced adhesion of neutrophils and CD4+ T cells to HUVEC. The findings that IL-3 can stimulate both proliferation and functional activation of endothelial cells suggest that this cytokine can be involved in sustaining the process of chronic inflammation.

Soluble c-kit proteins and antireceptor monoclonal antibodies confine the binding site of the stem cell factor

The binding of the stem cell factor (SCF) to the c-kit-encoded receptor tyrosine kinase stimulates a variety of biochemical responses that culminate in cellular proliferation, migration, or survival. The extracellular domain of p145kit consists of five immunoglobulin-like domains. To confine the ligand binding site to this portion of the receptor we generated a panel of murine monoclonal antibodies (mAbs) to the Kit protein and identified two mAbs that efficiently displaced receptor-bound SCF and also inhibited proliferation of SCF-dependent human megakaryocytes. To map the epitopes of these mAbs we constructed and expressed soluble portions of the extracellular domain of Kit, which included either the two amino-terminal Ig-like domains (denoted Kit 1-2), three Ig-like domains (Kit 1-2-3), or the entire extracellular portion (Kit-X). All three recombinant proteins were recognized by the ligand inhibitory mAbs, suggesting that the SCF binding site resides in the amino-terminal half of the ecto-domain. Consistent with this conclusion, all of the soluble proteins inhibited SCF binding to Kit-expressing cells, and they also underwent specific covalent cross-linking to the radiolabeled ligand. However, whereas Kit 1-2-3 and Kit-X displayed comparable ligand affinities, deletion of the third Ig-like domain, in Kit 1-2, involved significant reduction in SCF binding. Hence, the binding site of SCF probably includes Ig-like domains 1 and 2, but structural determinants distal to this portion may also participate in ligand recognition.

Effect of human interleukin 3 on the susceptibility of fresh leukemia cells to interleukin-2-induced lymphokine activated killing activity

Pretreatment of acute myeloblastic leukemia cells with the hemopoietic growth factor interleukin 3 (IL3) increased their susceptibility to lymphokine activated killing (LAK) but did not affect their constitutive resistance to native natural killer activity. In addition, IL3 treatment did not alter the LAK cell-mediated killing of CD34+ hemopoietic progenitors present in normal bone marrow. Increased 3H-thymidine uptake was generally observed after IL3 treatment. However, failure to proliferate in response to IL3, observed in some cases, did not prevent changes in LAK susceptibility. Enhanced lysis of IL3-treated leukemic cells was accompanied by a moderate increase of the effector-target binding. Increased LAK susceptibility was already observed at 18 h, while optimal cytolysis and expression of the cell adhesion molecule (CAM) LFA-3 (CD58) by IL3-treated AML cells were concomitantly observed at later culture times. In contrast, the CAM ICAM-1 (CD54) was not modulated by IL3, nor were significant changes in the expression of either CAMs observed in normal hemopoietic cells. Blocking experiments with the anti-CD58 monoclonal antibody demonstrated a variable neutralizing effect on the IL3-induced increase of LAK activity, depending on the leukemia cell studied. The effect described here, together with the known role of IL3 in normal hemopoiesis makes it a factor of potential therapeutic value for the treatment of leukemic patients.

Generation of human monoclonal antibodies that confer protection against pertussis toxin

A panel of human monoclonal antibodies reactive with pertussis toxin has been generated by means of Epstein-Barr virus infection. One of these, the 3F11 monoclonal antibody, showed the ability to neutralize in vitro and in vivo the toxic effects of the toxin. Western blot (immunoblot) analysis located the 3F11 epitope on the S3 subunit.

GM-CSF and phorbol esters modulate GM-CSF receptor expression by independent mechanisms

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) (0.1 nM) down-modulates its receptor in IL-3/GM-CSF dependent M-07e cells, in KG-1 cells and normal granulocytes, whereas phorbol esters 12-O-tetradecanoylphorbol-13-acetate (TPA) (2 nM) down-modulates the GM-CSF receptor in M-07e cells and granulocytes but not in KG-1 cells. As data analysis shows by nonlinear regression, the decreased binding ability depends on a reduction of the binding sites with no significant change of their dissociation constant. To gain insight into the mechanisms involved in the GM-CSF receptor regulation, we investigated the role of protein kinase C (PKC). GM-CSF, unlike TPA, was unable to activate PKC in all the cells studied. Moreover, unlike TPA, GM-CSF was still able to down-modulate its receptor in cells where PKC was inhibited by 1-(5-isoquinolonesulphonyl)-2-methylpiperazine (H7) and staurosporine or in cells where PKC was exhausted by prolonged incubation with 1 microM TPA. Finally, the receptor re-expression rate was accelerated by protein kinases inhibitors. These results, taken together, indicate the presence of a PKC-dependent and -independent down-modulation mechanism and a negative role of the endogeneous protein kinases in GM-CSF receptor re-expression.

Hematopoietic growth factor receptors

The molecular cloning for most of the hematopoietic growth factor receptors has been achieved over the past few years and revealed that they can by assigned to two discrete receptor families, namely the hematopoietic growth factor superfamily (HRS) and the receptor tyrosine kinase family (RTK). The members of the HRS, including granulocyte-macrophage colony-stimulating factor receptor (GM-CSF-R), interleukin 3 receptor (IL-3-R), granulocyte CSF receptor (G-CSF-R) and erythropoietin receptor (Epo-R), share a common binding domain and the absence of a tyrosine kinase domain in their cytoplasmic portion. In some cases (e.g., GM-CSF-R), the high-affinity receptor structure is obtained through the association of the low-affinity binding chain (alpha chain) with an accessory protein (beta chain). It is conceivable that this protein might also represent the common subunit shared by GM-CSF-R and by IL-3-R when they are co-expressed to form the putative GM-CSF-R/IL-3-R complex. Although tyrosine phosphorylation following ligand receptor activation seems to be a common event in the HRS, its role in the signal transduction mechanisms is unknown. Due to the structural analogies among the members of this family any new insight into one particular receptor member, such as its subunit structure and its signal transduction pathways, will be generalizable to the other family members. The subclass III of the RTK family, including the CSF-1-R and c-kit, is characterized by an additional insert into the kinase domain that recognizes and binds protein substrates. Ligand induced activation of the kinase domain and its signaling potential are mediated by receptor oligomerization which stabilizes interactions between adjacent cytoplasmic domains and leads to activation of kinase function by molecular interaction. Interestingly, the receptors included in this subclass are the products of well known cellular proto-oncogenes. A large variety of structural alteration found in receptor-derived oncogene products may lead to constitutive activation of receptor signals that, consequently, result in the subversion of the mechanisms controlling the cell growth.

Interleukin 3-dependent proliferation of the human Mo-7e cell line is supported by discrete activation of late G1 genes

The hemopoietic growth factor interleukin 3 (IL-3) supports the survival and proliferation of multipotent and committed progenitor cells in vitro. To elucidate the molecular mechanisms triggered by IL-3 we studied the expression of cell cycle-related genes in a recently established human IL-3-dependent clone (M-07e). No changes in the level of expression of early (c-myc), mid (ornithine decarboxylase), or mid-late G1 (p53, c-myb) cell cycle genes were detected after restoration of IL-3 in deprived cells. The fact that only late G1-S-phase genes [proliferating cell nuclear antigen (PCNA) thymidine kinase (TK), histone H3] are modulated by IL-3 suggests that this factor may control human cell proliferation by acting at the G1-S boundary.

M-07e human leukemic factor-dependent cell line provides a rapid and sensitive bioassay for the human cytokines GM-CSF and IL-3

We have isolated a subline of the M-07 human megakaryoblastic leukemia cell line, designated M-07e, that requires either interleukin-3 (IL-3) or granulocyte macrophage colony-stimulating factor (GM-CSF) for growth, even in the presence of fetal calf serum. This cell line will not grow long term in any other cytokine although it responds slightly to IL-2, IL-4, IL-6, IL-9, and interferon-gamma. We have used the M-07e subline to develop a quantitative bioassay for the measurement of levels of either GM-CSF or IL-3. This assay is as sensitive to either factor as the human bone marrow colony assay (CFU-GM) or the chronic myelogeneous leukemic (CML) blast cell proliferation assay for these factors and is much more convenient and reliable than either. With this assay, as little as 25-50 pg/ml of either IL-3 or GM-CSF can be detected, a level that should render the assay useful for analysis of these molecules in samples from patients undergoing colony-stimulating factor therapy and from conditioned media from natural sources of the factors. In these cases, neutralizing antisera to each cytokine are required to demonstrate the specificity of the assay. This assay, in combination with quantitative immunoassays, should greatly facilitate the analysis of the roles of IL-3 and GM-CSF in regulating hematopoiesis both in patients and in natural sources of the cytokines.

Rearrangements and aberrant expression of the retinoic acid receptor alpha gene in acute promyelocytic leukemias

Although acute promyelocytic leukemias (APLs) are consistently associated with a reciprocal chromosome 15;17 translocation, the gene(s) directly affected by the breakpoints have never been isolated. The chromosome 17 breakpoint maps to near the retinoic acid receptor alpha (RAR alpha) locus. Investigation of 20 APLs and a large series of other neoplastic patients and normal controls revealed RAR alpha gene rearrangements and aberrant transcripts only in the APL cases. These findings suggest that the RAR alpha gene is involved in the APL chromosome 17 breakpoint, is implicated in leukemogenesis, and could be used as a marker for identifying leukemic promyelocytes.

Mapping of chromosome 17 breakpoints in acute myeloid leukemias

The 17q11-21 chromosomal region is frequently involved in non-random structural rearrangements associated with the M1 and M2 subtypes of acute myeloid leukemias (AML), as well as with the 15;17 translocation typical of the promyelocytic subtype. A number of genes have been localized in this region including the c-erbA-1 and c-erbB-2 proto-oncogenes, the genes coding for the granulocyte-colony stimulating factor (G-CSF), the retinoic acid receptor alpha (RAR alpha) and the myeloperoxidase enzyme (MPO). However, the precise location of these genes in relationship to the 17q11-21 breakpoint(s) has not been determined. Using in situ hybridization on metaphase chromosomes, we established the position of the breakpoints in relationship to the c-erbA-1, c-erbB-2, G-CSF, RAR alpha and MPO loci in a series of AML cases bearing 17q11-21 rearrangements. We report: (i) that the respective position of the five genes is centromere - c-erbA-1 - G-CSF - c-erbB-2 - RAR alpha - MPO - telomere; (ii) that the breakpoints of the various AML subtypes are variably located between the centromere and c-erbB-2 in M1 and M2; (iii) that the breakpoints are consistently located between c-erbB-2 and RAR alpha/MPO in M3; and (iv) that the breakpoint on chromosome 17 in the 15;17 translocation is located on 17q21 and not on 17q11-12 as previously reported.

Evidence for a role of the Na+/H+ exchanger in the colony-stimulating-factor-induced ornithine decarboxylase activity and proliferation of the human cell line M-07e

The subclone M-07e, derived from the interleukin-3 (IL-3)-responsive human myeloid cell line M-07, is strictly dependent on either IL-3 or granulocyte-macrophage-colony-stimulating factor (GM-CSF) for its growth and survival. This cell line may be regarded as a candidate model to investigate the poorly understood events triggered by growth factors binding to human hemopoietic cells. Both IL-3 and GM-CSF induce in M-07e cells an increase of ornithine decarboxylase (ODC) activity, which reaches its maximum at 24-30 h and fully depends on de novo protein synthesis. The growth factors do not elicit translocation of protein kinase C to the membrane; thus a role of the kinase in ODC induction is ruled out. An amiloride-inhibitable Na+/H+ exchanger is present in the membrane of M-07e cells; its apparent Km for extracellular Na+ is 47.77 mM; and its activity is greatly enhanced when the cytoplasm is acidified. Growth-factor-evoked ODC activation and DNA synthesis are blocked in a dose- and time-dependent manner when M-07e cells are incubated with ethylisopropylamiloride, a specific inhibitor of Na+/H+ exchanger. The exchanger does not appear to be directly activated by IL-3 or GM-CSF, but its operation is strictly required for the biological effects of these growth factors on M-07e cell line.

Expression and modulation of IL-3 and GM-CSF receptors in human growth factor dependent leukaemic cells

From the interleukin-3 (IL-3) responsive human myeloid cell line M-07 we derived a subclone, named M-07e, which is fully dependent for growth and survival on either granulocyte-macrophage colony stimulating factor (GM-CSF) or IL-3. In this paper the expression, specificity and modulation of GM-CSF and IL-3 receptors on M-07e cells are described. The specificity of the binding was demonstrated by the failure of other cytokines to compete, at 4 degrees C, with GM-CSF or IL-3 receptors. In addition, IL-3 was found to compete as well as GM-CSF for GM-CSF receptors while GM-CSF was a weak competitor for IL-3 receptors. Quantitative binding studies and Scatchard plot analysis revealed the presence of a single class of high-affinity GM-CSF binding sites (405 +/- 27.4 sites per cell, dissociation constant at the equilibrium 52 +/- 20 pM) and the presence of high and low-affinity regions for IL-3 binding sites (27 +/- 12 and 416 +/- 92 sites per cell for the high and low affinity regions respectively, dissociation constant at the equilibrium, 58 +/- 22 pM and 5.7 +/- 2.0 nM respectively). Finally, in agreement with the hierarchical down-modulation model, we found that IL-3 can down-modulate both IL-3 and GM-CSF receptors while GM-CSF can down-modulate only its own receptors. The present results suggest that M-07e cells, in spite of their neoplastic nature, share, with murine bone marrow cells, similar growth factor receptor regulatory mechanisms. This cell line may be regarded as a candidate model to investigate the physiological events triggered by growth factors binding to human haemopoietic cells.

Different sensitivity of normal and leukaemic progenitor cells to Ara-C and IL-3 combined treatment

In the present study the effects of a combined treatment with cytosine-arabinoside (Ara-C) and interleukin-3 (IL-3) on acute myeloblastic leukaemia clonogenic cells and on normal haemopoietic progenitors was investigated, with the aim of improving the tumoricidal effect of cycle specific drugs. Blast cells from 24 acute myeloblastic leukaemia (AML) patients were screened with a short-term proliferative assay based on 3H-thymidine (3H-TdR) uptake for their response to IL-3. To evaluate the synergism between the growth factor and Ara-C, the cells were pretreated for 3 d in liquid culture in the presence or absence of IL-3 (10 U/ml) and for the last 24 h with Ara-C (3 micrograms/ml). The cells were then washed and seeded in semisolid media to assess their clonogenic ability. The results showed that, in those cases which were good responders to IL-3 in the 3H-TdR uptake assay (19 out of 24), Ara-C exposure eliminated a greater proportion of clonogenic cells if pretreated with IL-3 than if untreated (P less than 0.001), while in cases unresponsive to IL-3 this effect was not significant. Moreover, when the same protocol was applied to bone marrow cells from normal donors, it was found that IL-3 pretreatment did not significantly enhance the toxic effect of Ara-C on day 14 granulocyte-macrophage colony forming units (CFU-GM) and erythroid burst forming units (BFU-E). Finally IL-3 pretreatment was also able to increase the cytotoxic effect of Ara-C on leukaemic cells co-cultured, to simulate clinical AML remission, with normal bone marrow cells. The results indicate that IL-3 may improve the therapeutic index of cycle-specific drugs in AML therapy.

Haematologic abnormalities in the acquired immunodeficiency syndrome

During the clinical history of HIV infection, haematological abnormalities represent a common finding which not only contributes to worsening the clinical condition but also limit the use of antibacterial as well as antiviral agents. On the basis of the regulatory role played by the immune system on haemopoiesis, in the present review the foremost derangements of the immunoregulatory circuits are first discussed. The main functional and quantitative defects of peripheral blood erythrocytes, granulocytes, platelets and monocytes are then analysed, and the different bone marrow pictures observed during the progression of the disease are described. To elucidate the physiophatogenetic mechanisms responsible for bone marrow and peripheral cytopenia, the most relevant in vitro studies are reported and discussed. These studies suggest that both a direct cytopathic effect of HIV on haemopoietic progenitors and an immune system mediated mechanism are involved. In view of the HIV selective tropism for lymphocytes and macrophages, which are a major source of haemopoietic growth factors, the new therapeutical strategies for the treatment of cytopenias based on exogenous administration of these cytokines, alone or in combination with antiviral drugs, are briefly reported.

Interleukin 2 does not promote the in vitro and in vivo proliferation and growth of human acute leukaemia cells of myeloid and lymphoid origin

The effect of recombinant interleukin 2 (IL2) on the in vitro and in vivo proliferation and growth of human acute leukaemia cells of both myeloid and lymphoid origin was investigated. In none of the 25 primary samples tested could a continuously in vitro growing cell line be obtained by adding IL2 to the culture medium. Although IL2 induced a proliferative signal in three of the 31 acute leukaemias analysed, the overall 3H-thymidine uptake of the neoplastic cells was significantly reduced (P less than 0.05) in the presence of IL2. The unlikelihood of an important proliferative signal triggered by IL2 was confirmed in a semisolid clonogenic assay, which failed to document an increased colony growth in the 26 samples studied. Furthermore, using a colorimetric assay as a test for cell proliferation and survival, in seven of the 11 fresh acute leukaemia samples tested a 22-40% reduction in viability was observed in the presence of IL2, while in the remaining four, IL2 was ineffective. In order to investigate the effect of IL2 in an in vivo setting, an experimental model in heavily immunosuppressed nu/nu mice was established. In no case did IL2 promote the in vivo proliferation and growth of human myeloid and lymphoid acute leukaemia cells injected in the mice. On the contrary, with seven of the eight leukaemic cell lines which gave rise spontaneously to leukaemic masses, this could be prevented when the mice received locally 300 U of IL2 three times daily for 90 d. IL2 also blocked the growth in vivo of three fresh acute leukaemia samples (two myeloid and one lymphoid). Co-culture experiments using leukaemic cell lines and increasing numbers of normal lymphocytes suggest that the inhibitory effect of IL2 is probably exerted via an indirect mechanism. These findings, coupled to the well-documented ability of IL2 to generate lymphokine activated killer cells cytolytic against leukaemic blasts, further point to the potential role of immunotherapy with IL2 in the management of patients with haematological malignancies.

Trisomy 11 in myelodysplastic syndrome-derived acute myeloblastic leukaemias

Here we report 3 cases of trisomy 11 observed in 1 patient with secondary acute myeloblastic leukaemia and in 2 patients with spontaneous acute myeloblastic leukaemia. In all 3 patients, the picture of overt acute leukaemia arose following a clinically established myelodysplastic syndrome. These findings, together with the previously reported occurrence of trisomy 11 in myelodysplastic syndrome and in acute myeloblastic leukaemia, suggest that this abnormality can be considered specifically associated with myelodysplastic syndrome and with the subsequent and related acute myeloblastic leukaemia.