Human AML colony growth in serum-free culture

Automated and closed clinical-grade manufacturing protocol produces potent NK cells against neuroblastoma cells and AML blasts

Natural killer (NK) cells are a promising allogeneic immunotherapy option due to their natural ability to kill tumor cells, and due to their apparent safety. This study describes the development of a GMP-compliant manufacturing protocol for the local production of functionally potent NK cells tailored for high-risk acute myeloid leukemia (AML) and neuroblastoma (NBL) patients. Moreover, the quality control strategy and considerations for product batch specifications in early clinical development are described. The protocol is based on the CliniMACS Prodigy platform and Natural Killer Cell Transduction (NKCT) (Miltenyi Biotec). NK cells are isolated from leukapheresis through CD3 depletion and CD56 enrichment, followed by a 12-hour activation with IL-2 and IL-15 cytokines. Three CliniMACS Prodigy processes demonstrated the feasibility and consistency of the modified NKCT process. A three-step process without expansion, however, compromised the NK cell yield. T cells were depleted effectively, indicating excellent safety of the product. Characterization of the NK cells before and after cytokine activation revealed a notable increase in the expression of activation markers, particularly CD69, consistent with enhanced functionality. Intriguingly, the NK cells exhibited increased killing efficacy against patient-derived CD33 + AML blasts and NBL cells in vitro, suggesting a potential therapeutic benefit in AML and NBL.

Pretransplant Systemic Lipidomic Profiles in Allogeneic Stem Cell Transplant Recipients

Simple Summary

Stem cell transplantation is used in the treatment of aggressive hematological malignancies and consists of initial high-dose and potentially lethal chemotherapy, followed by rescue with the transplantation of hematopoietic stem cells. Transplantation with stem cells from a healthy donor (i.e., allogeneic stem cells) has the strongest anti-cancer effect, but also the highest risk of severe toxicity. Furthermore, the clinical status at the time of transplantation (inflammation, fluid overload) is associated with posttransplant mortality, and immune-mediated acute graft-versus-host disease (GVHD) is a potential lethal complication. Finally, lipid metabolism regulates the proliferation and survival of both malignant hematological cells and immunocompetent cells that cause GVHD. Our study shows that the pretransplant lipid profiles differ between allotransplant recipients and can be used for the subclassification of patients and possibly to identify patients with an increased risk of death due to disease relapse or treatment toxicity. The therapeutic targeting of lipid metabolism should therefore be further explored in these transplant recipients.

Abstract

Allogeneic stem cell transplantation is used in the treatment of high-risk hematological malignancies. However, this treatment is associated with severe treatment-related morbidity and mortality. The metabolic status of the recipient may be associated with the risk of development of transplant-associated complications such as graft-versus-host disease (GVHD). To better understand the impact of the lipidomic profile of transplant recipients on posttransplant complications, we evaluated the lipid signatures of patients with hematological disease using non-targeted lipidomics. In the present study, we studied pretransplant serum samples derived from 92 consecutive patients with acute myeloid leukemia (AML) or high-risk myelodysplastic syndrome (MDS). A total of 960 lipid biochemicals were identified, and the pretransplant lipidomic profiles differed significantly when comparing patients with and without the risk factors: (i) pretransplant inflammation, (ii) early fluid overload, and (iii) patients with and without later steroid-requiring acute GVHD. All three factors, but especially patients with pretransplant inflammation, were associated with decreased levels of several lipid metabolites. Based on the overall concentrations of various lipid subclasses, we identified a patient subset characterized by low lipid levels, increased frequency of MDS patients, signs of inflammation, decreased body mass index, and an increased risk of early non-relapse mortality. Metabolic targeting has been proposed as a possible therapeutic strategy in allotransplant recipients, and our present results suggest that the clinical consequences of therapeutic intervention (e.g., nutritional support) will also differ between patients and depend on the metabolic context.

Current challenges in the manufacture of clinical-grade autologous whole cell vaccines for hematological malignancies

Autologous whole cell vaccines use a patient's own tumor cells as a source of antigen to elicit an anti-tumor immune response in vivo. Recently, the authors conducted a systematic review of clinical trials employing these products in hematological cancers that showed a favorable safety profile and trend toward efficacy. However, it was noted that manufacturing challenges limit both the efficacy and clinical implementation of these vaccine products. In the current literature review, the authors sought to define the issues surrounding the manufacture of autologous whole cell products for hematological cancers. The authors describe key factors, including the acquisition, culture, cryopreservation and transduction of malignant cells, that require optimization for further advancement of the field. Furthermore, the authors provide a summary of pre-clinical work that informs how the identified challenges may be overcome. The authors also highlight areas in which future basic research would be of benefit to the field. The goal of this review is to provide a roadmap for investigators seeking to advance the field of autologous cell vaccines as it applies to hematological malignancies.

Effects of insulin and pathway inhibitors on the PI3K-Akt-mTOR phosphorylation profile in acute myeloid leukemia cells

The phosphatidylinositol 3-kinase (PI3K)-Akt-mechanistic target of rapamycin (mTOR) pathway is constitutively activated in human acute myeloid leukemia (AML) cells and is regarded as a possible therapeutic target. Insulin is an agonist of this pathway and a growth factor for AML cells. We characterized the effect of insulin on the phosphorylation of 10 mediators in the main track of the PI3K-Akt-mTOR pathway in AML cells from 76 consecutive patients. The overall results showed that insulin significantly increased the phosphorylation of all investigated mediators. However, insulin effects on the pathway activation profile varied among patients, and increased phosphorylation in all mediators was observed only in a minority of patients; in other patients, insulin had divergent effects. Global gene expression profiling and proteomic/phosphoproteomic comparisons suggested that AML cells from these two patient subsets differed with regard to AML cell differentiation, transcriptional regulation, RNA metabolism, and cellular metabolism. Strong insulin-induced phosphorylation was associated with weakened antiproliferative effects of metabolic inhibitors. PI3K, Akt, and mTOR inhibitors also caused divergent effects on the overall pathway phosphorylation profile in the presence of insulin, although PI3K and Akt inhibition caused a general reduction in Akt pT308 and 4EBP1 pT36/pT45 phosphorylation. For Akt inhibition, the phosphorylation of upstream mediators was generally increased or unaltered. In contrast, mTOR inhibition reduced mTOR pS2448 and S6 pS244 phosphorylation but increased Akt pT308 phosphorylation. In conclusion, the effects of both insulin and PI3K-Akt-mTOR inhibitors differ between AML patient subsets, and differences in insulin responsiveness are associated with differential susceptibility to metabolic targeting.

The Capacity of Long-Term in Vitro Proliferation of Acute Myeloid Leukemia Cells Supported Only by Exogenous Cytokines Is Associated with a Patient Subset with Adverse Outcome

Acute myeloid leukemia (AML) is an aggressive malignancy, which is highly heterogeneous with regard to chemosensitivity and biological features. The AML cell population is organized in a hierarchy that is reflected in the in vitro growth characteristics, with only a minority of cells being able to proliferate for more than two weeks. In this study, we investigated the ability of AML stem cells to survive and proliferate in suspension cultures in the presence of exogenous mediators but without supporting non-leukemic cells. We saw that a high number of maintained stem cells (i.e., a large number of clonogenic cells after five weeks of culture) was associated with decreased overall survival for patients receiving intensive chemotherapy; this prognostic impact was also detected in the multivariate/adjusted analysis. Furthermore, the patients with many clonogenic cells presented more frequently with mutations in transcription-related genes, and also showed a higher abundance of proteins involved in transcription at the time of diagnosis. In conclusion, the growth characteristics of the long-term proliferating leukemic stem cells seem to have an independent prognostic impact in human AML, and these characteristics appear to be reflected by the mutational landscape and the proteome of the patients at the time of diagnosis.

Resistance to the Antiproliferative In Vitro Effect of PI3K-Akt-mTOR Inhibition in Primary Human Acute Myeloid Leukemia Cells Is Associated with Altered Cell Metabolism

Constitutive signaling through the phosphatidylinositol-3-kinase-Akt-mechanistic target of rapamycin (PI3K-Akt-mTOR) pathway is present in acute myeloid leukemia (AML) cells. However, AML is a heterogeneous disease, and we therefore investigated possible associations between cellular metabolism and sensitivity to PI3K-Akt-mTOR pathway inhibitors. We performed non-targeted metabolite profiling to compare the metabolome differences of primary human AML cells derived from patients susceptible or resistant to the in vitro antiproliferative effects of mTOR and PI3K inhibitors. In addition, the phosphorylation status of 18 proteins involved in PI3K-Akt-mTOR signaling and the effect of the cyclooxygenase inhibitor indomethacin on their phosphorylation status was investigated by flow cytometry. Strong antiproliferative effects by inhibitors were observed only for a subset of patients. We compared the metabolite profiles for responders and non-responders towards PI3K-mTOR inhibitors, and 627 metabolites could be detected. Of these metabolites, 128 were annotated and 15 of the annotated metabolites differed significantly between responders and non-responders, including metabolites involved in energy, amino acid, and lipid metabolism. To conclude, leukemia cells that are susceptible or resistant to PI3K-Akt-mTOR inhibitors differ in energy, amino acid, and arachidonic acid metabolism, and modulation of arachidonic acid metabolism alters the activation of mTOR and its downstream mediators.

Vacuolar ATPase as a possible therapeutic target in human acute myeloid leukemia

INTRODUCTION

V-ATPase is a proton pump expressed both in the membrane of intracellular organelles (e.g. endosomes, lysosomes, Golgi structures) and the plasma membrane. It is an important regulator of organellar functions, intracellular molecular trafficking, intercellular communication and intracellular signaling. It is therefore considered as a possible therapeutic target in the treatment of human malignancies. Areas covered: Relevant publications were identified through literature searches in the PubMed database. We searched for original articles and reviews describing the possible importance of V-ATPase for leukemogenesis and chemosensitivity in human myeloid cells, especially acute myeloid leukemia (AML) cells. Expert commentary: The expression of V-ATPase in the primary human AML cells varies between patients, and high levels are associated with high constitutive release of a wide range of soluble mediators. Several of the molecules included in the V-ATPase interactome may also be important in leukemogenesis and/or development of chemoresistance in human AML. Therapeutic targeting of V-ATPase should therefore be regarded as a possible therapeutic strategy in human AML, but the efficiency of such targeting will probably differ between patients. The possibility of toxicity, especially hematological toxicity and immunosuppression, also has to be clarified.

Patients with acute myeloid leukemia can be subclassified based on the constitutive cytokine release of the leukemic cells; the possible clinical relevance and the importance of cellular iron metabolism

OBJECTIVE

Acute myeloid leukaemia (AML) is a heterogeneous malignancy; we studied how the constitutive cytokine release by the AML cells varies among patients.

METHODS

We investigated the constitutive release of 28 mediators during in vitro culture for 79 consecutive patients.

RESULTS

Constitutive cytokine release profiles differed among patients, and hierarchical clustering identified three subsets with high, intermediate and low release, respectively. The high-release subset showed high levels of most mediators, usually monocytic differentiation as well as altered mRNA expression of proteins involved in intracellular iron homeostasis and molecular trafficking; this subset also included 4 out of 6 patients with inv(16). Spontaneous in vitro apoptosis did not differ among the subsets. For the high-release patients, cytokines were released both by CD34⁺ and CD34^- cells. The mRNA and released protein levels showed statistically significant correlations only for eleven of the cytokines. The overall survival after intensive anti-leukemic therapy was significantly higher for high-release compared with low-release patients. Pharmacological targeting of iron metabolism (iron chelation, transferrin receptor blocking) altered the cytokine release profile.

CONCLUSIONS

Subclassification of AML patients based on the constitutive cytokine release may be clinically relevant and a part of a low-risk (i.e. chemosensitive) AML cell phenotype.

Expression of the potential therapeutic target CXXC5 in primary acute myeloid leukemia cells - high expression is associated with adverse prognosis as well as altered intracellular signaling and transcriptional regulation

The CXXC5 gene encodes a transcriptional activator with a zinc-finger domain, and high expression in human acute myeloid leukemia (AML) cells is associated with adverse prognosis. We now characterized the biological context of CXXC5 expression in primary human AML cells. The global gene expression profile of AML cells derived from 48 consecutive patients was analyzed; cells with high and low CXXC5 expression then showed major differences with regard to extracellular communication and intracellular signaling. We observed significant differences in the phosphorylation status of several intracellular signaling mediators (CREB, PDK1, SRC, STAT1, p38, STAT3, rpS6) that are important for PI3K-Akt-mTOR signaling and/or transcriptional regulation. High CXXC5 expression was also associated with high mRNA expression of several stem cell-associated transcriptional regulators, the strongest associations being with WT1, GATA2, RUNX1, LYL1, DNMT3, SPI1, and MYB. Finally, CXXC5 knockdown in human AML cell lines caused significantly increased expression of the potential tumor suppressor gene TSC22 and genes encoding the growth factor receptor KIT, the cytokine Angiopoietin 1 and the selenium-containing glycoprotein Selenoprotein P. Thus, high CXXC5 expression seems to affect several steps in human leukemogenesis, including intracellular events as well as extracellular communication.

Cell viability of acute myeloid leukaemia blasts in culture correlates with treatment outcome

Despite the advances in understanding the pathophysiology of acute myeloid leukaemia (AML), the cure rate for acute myeloid leukaemia patients remains low. Cytogenetic abnormalities and age are the prognostic factors that guide treatment decisions. However, many AML patients still die. The biological factors that influence treatment outcome are largely unknown. Thus, the objective of our study was to use the in vitro viability test to correlate with treatment outcome. Acute myeloid leukaemia blasts demonstrated differing ability to survive in culture. Our examination of blast phenotype at various days in culture showed two possible growth directions. First, cells underwent maturation by increased expression of CD16 and down-regulated CD34 (a haemopoietic stem cell marker). These cells also appeared to have undergone apoptosis. Alternatively, cells continued to survive in culture and maintained high expression of CD34. An MTT assay was carried out to determine viability after three days of culture. Lower optical density values were obtained for samples that underwent apoptosis and higher values were obtained for samples that survived in culture. Apoptosis was measured by Annexin V/propidium iodide staining. A comparison between results of MTT assay and duration of disease free survival revealed that a higher viability in vitro correlated significantly with shorter survival duration in the patient (R -0.761, p=0.002, n=13). Thus, this study further supports the hypothesis that AML patients with poor survival may be related to having blasts with a biologically more immature or stem cell-like nature.

The peripheral cannabinoid receptor Cb2, a novel oncoprotein, induces a reversible block in neutrophilic differentiation

We previously identified a novel common virus integration site, Evi11, by means of retroviral insertional mutagenesis. We demonstrated that the gene encoding the peripheral cannabinoid receptor (Cb2) is the potential target, suggesting that Cb2 is a proto-oncogene. To elucidate a role for this G protein-coupled receptor (GPCR) in leukemic transformation we generated a Cb2-EGFP cDNA construct that was introduced into 32D/G-CSF-R cells. These cells require interleukin 3 (IL-3) to proliferate in vitro, whereas in the presence of granulocyte-colony-stimulating factor (G-CSF) they differentiate toward mature neutrophils. We demonstrate that 32D/G-CSF-R/Cb2-EGFP cells migrate in a transwell assay in reponse to the Cb2 ligand 2-arachidonoylglycerol (2-AG), indicating that the fusion protein was functional. When cultured in the presence of G-CSF neutrophilic differentiation of Cb2-EGFP-expressing 32D/G-CSF-R cells was completely blocked. Moreover, a Cb2-specific antagonist fully recovered the G-CSF-induced neutrophilic differentiation of 32D/G-CSF-R/Cb2-EGFP cells. To investigate which signal transduction pathway(s) may be involved in the block of neutrophilic maturation, differentiation experiments were carried out using specific inhibitors of signaling routes. Interestingly, full rescue of G-CSF-induced neutrophilic differentiation was observed when cells were cultured with the mitogen-induced extracellular kinase (MEK) inhibitors, PD98059 or U0126, and partial recovery was detected with the phosphoinositide 3-kinase (PI3-K) inhibitor LY-294002. These studies demonstrate that the Cb2 receptor is an oncoprotein that blocks neutrophilic differentiation when overexpressed in myeloid precursor cells. Cb2 appears to mediate its activity through MEK/extracellular signal-related kinase (ERK) and PI3-K pathways.

New strategies in the treatment of acute myelogenous leukemia (AML): in vitro culture of aml cells--the present use in experimental studies and the possible importance for future therapeutic approaches

In vitro studies of cultured native acute myelogenous leukemia (AML) blasts and cell lines have contributed significantly to our present knowledge about the pathogenesis of AML. In the present article we review different techniques for preparation and in vitro culture of AML blasts. Well-characterized serum-free in vitro conditions can now be used in experimental studies of AML, and this makes comparisons between different studies easier. We also describe assays for characterization of AML progenitor subsets (i.e., suspension cultures, colony assays, long-term in vitro culture, xenotransplantation in immunocompromised mice), and we discuss the possible use of AML cell lines as experimental models in AML. Furthermore, clinical studies suggest that the in vitro growth characteristics of AML blasts assayed by short-term culture of the total native populations can be used as a predictor of prognosis after intensive chemotherapy. These in vitro assays may therefore be used for more accurate identification of prognostic parameters and thereby form a basis for the development of simplified laboratory techniques suitable for routine evaluation of patients undergoing risk-adapted therapy. However, it will be equally important to further evaluate the clinical relevance of assays for primitive AML progenitors, and to develop simplified methods that can be used to characterize these progenitor subsets in the routine clinical evaluation.

In vitro culture of human acute myelogenous leukemia (AML) cells in serum-free media: studies of native AML blasts and AML cell lines

The functional characteristics were compared for acute myelogenous leukemia (AML) cells (native blasts and AML cell lines) cultured in three serum-free media (X-vivo 10, X-vivo 15, [Bio-Whitacker, Walkersville, MD] and StemSpan [Stem Cell Technologies, Vancouver, BC, Canada]) and in medium containing 10% inactivated fetal calf serum (FCS). For native AML blasts the following functions were compared: (1) autonomous and cytokine-dependent proliferation; (2) frequency of clonogenic cell; and (3) constitutive cytokine secretion. AML blast proliferation differed between patients independent of the culture medium used, and clonogenic cells were maintained after in vitro culture in all media. In contrast, constitutive cytokine secretion was higher for cells cultured in StemSpan and FCS-containing medium than for cells cultured in the X-vivo media. Native AML blasts incubated in StemSpan also showed a low frequency of apoptotic cells. The three serum-free media could also be used for long-term expansion of well-characterized AML cell lines, but the optimal medium for cell expansion and cytokine secretion differed between cell lines. We conclude that standardized serum-free culture conditions can be used for in vitro studies of native AML blasts and AML cell lines.

In vitro culture of acute myelogenous leukemia blasts: a comparison of four different culture media

Proliferative responses and cytokine secretion were compared when AML blasts were cultured in the three serum-free media, X-Vivo 10, X-Vivo 15, and defined serum-free medium (IMDM with mercaptoethanol, low-density lipoprotein, albumin, and transferrin) and in media containing 10% inactivated fetal bovine serum (FBS). The following AML blast functions were investigated: (a) constitutive cytokine secretion, (b) autonomous and cytokine-dependent proliferation, and (c) accessory cell function during T cell activation. Constitutive cytokine secretion and accessory cell function differed markedly when using different culture media. For the constitutive AML blast secretion of IL-1beta, IL-6, and tumor necrosis factor (TNF)-alpha, no qualitative differences were seen, but quantitative differences were observed with decreased cytokine levels for cells cultured in X-Vivo 10 and X-Vivo 15. The accessory cell function of AML blasts was also decreased in the X-Vivo media, whereas differences were less pronounced when comparing AML blast proliferation. Our results clearly demonstrate that a well-characterized culture system is essential for in vitro studies of AML blast functions.

Clonal growth of human acute leukemia cells in serum-free methylcellulose medium

The clonal growth of human acute leukemia cell line (K562) and acute myeloid leukemia cells in the serum-free culture (SFC) was studied in order to establish a SFC system which could replace the effects of serum by using semi-solid methylcellulose culture technique. Our results showed that the clonal growth of K562 cells in semi-solid culture was dependent on exogenous serum. The K562 could be grown in SFC supplemented with 4 major replacing substances. The multifactor and multilevel orthogonal experiment demonstrated that the colony formation was statistically influenced by the 4 replacing substances at various concentrations (P < 0.01). Among them, bovine serum albumin had greatest effect on clonal growth of K562 cells with the optimal concentration being 15 mg/L, followed by transferring, cholesterol and insulin with their optimal concentrations being of 150 mg/L, 7.8 mg/L and 7.0 mg/L respectively. SFC system was formed with the 4 substances at their optimal concentrations. Colony formation of the blast cells in 10 patients with acute myeloid leukemia was observed in this SFC system. There was a heterogeneity of acute myeloid leukemia cells among the 10 patients in response to the growth substances. In SFC system, there was a linear relationship between the number of the clonal formation and the count of the added cells, indicating the colony growth of the cells. Primary acute leukemia cells maintained in SFC system in 10 cases could completely form clones. The colony formation number in some cases in SFC system was more than that of the serum-containing culture. The SFC system could partially replace the serum for study of the clonal formation of human leukemia cells.

Butyrate-stable monosaccharide derivatives induce maturation and apoptosis in human acute myeloid leukaemia cells

The rapid degradation and subsequent lack of efficacy of n-butyric acid in vivo has been improved by the synthesis of monosaccharide stable pro-drugs of butyric acid. We studied the effects of D1 (O-n-butanoyl-2,3-O-isopropylidene-alpha-D-mannofuranoside), G1 (1-O-n-butanoyl-D,L-xylitol), and F1 (1-O-n-butanoyl 2,3-O-isopropylidene-D,L-xylitol) on the maturation and proliferation of AML cell lines HL 60 and FLG 29.1 and of purified blast cells from 10 cases of de novo acute myeloid leukaemia (AML). AML cell maturation was measured by surface antigen expression, morphology and cytochemistry. Toxicology in mice was also evaluated (DL50 1000 mg/kg). In HL 60 cells G1 and D1 increased the expression of CD15 and CD11a (presenting 62% of promyelo-metamyelocytes), and in 7/10 cases of primary AMLs that of CD11a, CD11b, CD15, and myeloperoxidase. D1, G1 and F1 induced a dose-dependent inhibition of tritiated thymidine uptake. Apoptosis (evaluated by flow cytometry and agarose gel electrophoresis) was induced in AML blasts by D1 and F1 (79% and 94% respectively for HL 60 cells) and, with less effect, by G1 (27%). The persistence of maturative and apoptotic activity in these new pro-drugs of butyric acid, hydrolysed only inside the tumour cell, suggests a possible use in differentiation therapy of myelodysplastic syndromes and AMLs.

Diphtheria Toxin Fused to Granulocyte-Macrophage Colony-Stimulating Factor Eliminates Acute Myeloid Leukemia Cells With the Potential to Initiate Leukemia in Immunodeficient Mice, But Spares Normal Hemopoietic Stem Cells

We studied the cell kill induced by granulocyte-macrophage colony-stimulating factor (GM-CSF ) fused to Diphtheria Toxin (DT-GM-CSF ) in acute myeloid leukemia (AML) samples and in populations of normal primitive hemopoietic progenitor cells. AML samples from three patients were incubated in vitro with 100 ng/mL DT-GM-CSF for 48 hours, and AML cell kill was determined in a proliferation assay, a clonogenic assay colony-forming unit-AML (CFU-AML) and a quantitative long-term bone marrow (BM) culture ie, the leukemic-cobblestone area forming cell assay (L-CAFC). To measure an effect on cells with in vivo leukemia initiating potential DT-GM-CSF exposed AML cells were transplanted into immunodeficient mice. In two out of three samples it was shown that all AML subsets, including those with long-term abilities in vivo (severe combined immunodeficient mice) and in vitro (L-CAFC assay) were reduced in number by DT-GM-CSF. Cell kill induced by DT-GM-CSF could be prevented by coincubation with an excess of GM-CSF, demonstrating that sensitivity to DT-GM-CSF is specifically mediated by the GM-CSF receptor. Therefore, binding and internalization of GM-CSF probably occur in immature AML precursors of these two cases of AML. The third AML sample was not responsive to either GM-CSF or DT-GM-CSF. The number of committed progenitors of normal bone marrow (burst-forming unit-erythroid, colony-forming unit granulocyte- macrophage, and cobble stone area forming cell [CAFC] week 2) and also the number of cells with long-term repopulating ability, assayed as week 6 CAFC, were unchanged after exposure to DT-GM-CSF (100 ng/mL, 48 hours). These studies show that DT-GM-CSF may be used to eliminate myeloid leukemic cells with long-term potential in vitro and in immunodeficient mice, whereas normal hemopoietic stem cells are spared.

Anandamide, a Natural Ligand for the Peripheral Cannabinoid Receptor Is a Novel Synergistic Growth Factor for Hematopoietic Cells

We recently demonstrated that the gene encoding the peripheral cannabinoid receptor (Cb2) may be a proto-oncogene involved in murine myeloid leukemias. We show here that Cb2 may have a role in hematopoietic development. RNAse protection analysis showed that Cb2 is normally expressed in spleen and thymus. Cb2 mRNA is also expressed in 45 of 51 cell lines of distinct hematopoietic lineages, ie, myeloid, macrophage, mast, B-lymphoid, T-lymphoid, and erythroid cells. The effect of the fatty acid anandamide, an endogenous ligand for cannabinoid receptors, on primary murine marrow cells and hematopoietic growth factor (HGF )-dependent cell lines was then investigated. In vitro colony cultures of normal mouse bone marrow cells showed anandamide to potentiate interleukin-3 (IL-3)–induced colony growth markedly. Whereas HGFs alone stimulate proliferation of the various cell lines in serum-free culture only weakly, anandamide enhances the proliferative response of the cell lines to HGFs profoundly. This was apparent for responses induced by IL-3, granulocyte-macrophage colony-stimulating factor, granulocyte colony-stimulating factor, and erythropoietin. Anandamide was already effective at concentrations as low as 0.1 to 0.3 μmol/L and plateau effects were reached at 0.3 to 3 μmol/L. The addition of anandamide as single growth factor had no effect. The costimulatory effect of anandamide was not evident when cells were cultured with fetal calf serum (FCS), suggesting that FCS contains anandamide or another ligand capable of activating the peripheral cannabinoid receptor. Other cannabinoid ligands did not enhance the proliferative responsiveness of hematopoietic cells to HGFs. Transfection experiments of Cb2 in myeloid 32D cells showed that anandamide specifically activates proliferation through activation of the peripheral cannabinoid receptor. Anandamide appears to be a novel and synergistic growth stimulator for hematopoietic cells.

Anandamide, a Natural Ligand for the Peripheral Cannabinoid Receptor Is a Novel Synergistic Growth Factor for Hematopoietic Cells

We recently demonstrated that the gene encoding the peripheral cannabinoid receptor (Cb2) may be a proto-oncogene involved in murine myeloid leukemias. We show here that Cb2 may have a role in hematopoietic development. RNAse protection analysis showed that Cb2 is normally expressed in spleen and thymus. Cb2 mRNA is also expressed in 45 of 51 cell lines of distinct hematopoietic lineages, ie, myeloid, macrophage, mast, B-lymphoid, T-lymphoid, and erythroid cells. The effect of the fatty acid anandamide, an endogenous ligand for cannabinoid receptors, on primary murine marrow cells and hematopoietic growth factor (HGF )-dependent cell lines was then investigated. In vitro colony cultures of normal mouse bone marrow cells showed anandamide to potentiate interleukin-3 (IL-3)–induced colony growth markedly. Whereas HGFs alone stimulate proliferation of the various cell lines in serum-free culture only weakly, anandamide enhances the proliferative response of the cell lines to HGFs profoundly. This was apparent for responses induced by IL-3, granulocyte-macrophage colony-stimulating factor, granulocyte colony-stimulating factor, and erythropoietin. Anandamide was already effective at concentrations as low as 0.1 to 0.3 μmol/L and plateau effects were reached at 0.3 to 3 μmol/L. The addition of anandamide as single growth factor had no effect. The costimulatory effect of anandamide was not evident when cells were cultured with fetal calf serum (FCS), suggesting that FCS contains anandamide or another ligand capable of activating the peripheral cannabinoid receptor. Other cannabinoid ligands did not enhance the proliferative responsiveness of hematopoietic cells to HGFs. Transfection experiments of Cb2 in myeloid 32D cells showed that anandamide specifically activates proliferation through activation of the peripheral cannabinoid receptor. Anandamide appears to be a novel and synergistic growth stimulator for hematopoietic cells.

Erythropoietin-Induced Activation of STAT5 Is Impaired in the Myelodysplastic Syndrome

Patients with myelodysplastic syndrome (MDS) have ineffective in vivo and in vitro erythropoiesis, characterized by an impaired response to erythropoietin (Epo). We examined proliferation and maturation of MDS marrow cells in response to Epo in more detail. Epo-dependent DNA synthesis as well as induction of GATA-1 binding activity in marrow cells from 15 MDS cases were severely reduced as compared with normal bone marrow (NBM). Additionally, the appearance of morphologically identifiable erythroid cells was decreased in MDS cell cultures. These data indicate that both the Epo-dependent proliferation as well as the differentiation induction by Epo is suppressed. To study more upstream events of the Epo signal transduction route we investigated activation of the signal transducer and activator of transcription (STAT) 5. In all 15 MDS samples tested, STAT5 activation was absent or greatly suppressed in response to Epo. In contrast, interleukin-3 induced a normal STAT5 response in MDS cells. Further, in MDS the subset of CD71+ BM cells that is phenotypically similar to Epo-responsive cells in normal marrow, was present. We conclude that the Epo response in MDS is disturbed at an early point in the Epo receptor (EpoR) signal transduction pathway.

Erythropoietin-Induced Activation of STAT5 Is Impaired in the Myelodysplastic Syndrome

Patients with myelodysplastic syndrome (MDS) have ineffective in vivo and in vitro erythropoiesis, characterized by an impaired response to erythropoietin (Epo). We examined proliferation and maturation of MDS marrow cells in response to Epo in more detail. Epo-dependent DNA synthesis as well as induction of GATA-1 binding activity in marrow cells from 15 MDS cases were severely reduced as compared with normal bone marrow (NBM). Additionally, the appearance of morphologically identifiable erythroid cells was decreased in MDS cell cultures. These data indicate that both the Epo-dependent proliferation as well as the differentiation induction by Epo is suppressed. To study more upstream events of the Epo signal transduction route we investigated activation of the signal transducer and activator of transcription (STAT) 5. In all 15 MDS samples tested, STAT5 activation was absent or greatly suppressed in response to Epo. In contrast, interleukin-3 induced a normal STAT5 response in MDS cells. Further, in MDS the subset of CD71+ BM cells that is phenotypically similar to Epo-responsive cells in normal marrow, was present. We conclude that the Epo response in MDS is disturbed at an early point in the Epo receptor (EpoR) signal transduction pathway.

AML1 fusion transcripts in t(3;21) positive leukemia: evidence of molecular heterogeneity and usage of splicing sites frequently involved in the generation of normal AML1 transcripts

The t(3;21)(q26;q22) is associated with chronic myelogenous leukemia in blast crisis (CML-BC), leukemia evolving from (therapy-related) myelodysplasia, and with leukemia following other hematopoietic proliferative diseases. Molecular cytogenetic analysis and cloning of a few t(3;21) cases indicate that the breakpoints are quite heterogeneous even within a specific clinical phenotype. Interestingly some of the (3;21) breakpoints involve the AML1 gene previously found rearranged in the t(8;21) associated with acute myelogenous leukemia. AML1 is related to the Drosophila gene runt and is the human counterpart of the gene for the alpha subunit of the nuclear polyoma enhancer binding protein (PEBP2) also known as the core binding factor (CBF). In the t(3;21) AML1 was found rearranged with EAP, a gene on chromosome 3 encoding a small ribosomal protein, as well as with EV11, another gene on chromosome 3. Here we report our study of six cases of t(3;21). By using fluorescence in situ hybridization (FISH) analysis and AML1 probes we could conclude that at least in two CML-BC cases the breakpoint occurred in the AML1 intron that is disrupted by the t(8;21). An AML1/EAP fusion transcript, different from the one described in a therapy-related myelodysplasia, was detected in both CML-BC cases. This transcript is expected to result in a predicted protein containing the AML1 nuclear binding domain with an attached stretch of 17 amino acids unrelated to the EAP small ribosomal protein. In the other t(3;21) patients we could not detect an AML1/EAP transcript or an AML1/EV11 transcript. This result suggests heterogeneity of the t(3;21) at the molecular level. The AML1 chimeric transcripts identified so far, both in the t(3;21) and in the t(8;21), diverge from the normal transcripts either after exon 5 or exon 6. Here we show that in normal AML1 transcripts different splicing events are seen to occur after AML1 exon 5 as well as exon 6.

Distinct cytoplasmic regions of the human granulocyte colony-stimulating factor receptor involved in induction of proliferation and maturation

The granulocyte colony-stimulating factor receptor (G-CSF-R) transduces signals important for the proliferation and maturation of myeloid progenitor cells. To identify functionally important regions in the cytoplasmic domain of the G-CSF-R, we compared the actions of the wild-type receptor, two mutants, and a natural splice variant in transfectants of the mouse pro-B cell line BAF3 and two myeloid cell lines, 32D and L-GM. A region of 55 amino acids adjacent to the transmembrane domain was found to be sufficient for generating a growth signal. The immediate downstream sequence of 30 amino acids substantially enhanced the growth signaling in the three cell lines. In contrast, the carboxy-terminal part of 98 amino acids strongly inhibited growth signaling in the two myeloid cell lines but not in BAF3 cells. Truncation of this region lead to an inability of the G-CSF-R to transduce maturation signals in L-GM cells. An alternative carboxy tail present in a splice variant of the G-CSF-R also inhibited growth signaling, notably in both the myeloid cells and BAF3 cells, but appeared not to be involved in maturation.

Distinct cytoplasmic regions of the human granulocyte colony-stimulating factor receptor involved in induction of proliferation and maturation

The granulocyte colony-stimulating factor receptor (G-CSF-R) transduces signals important for the proliferation and maturation of myeloid progenitor cells. To identify functionally important regions in the cytoplasmic domain of the G-CSF-R, we compared the actions of the wild-type receptor, two mutants, and a natural splice variant in transfectants of the mouse pro-B cell line BAF3 and two myeloid cell lines, 32D and L-GM. A region of 55 amino acids adjacent to the transmembrane domain was found to be sufficient for generating a growth signal. The immediate downstream sequence of 30 amino acids substantially enhanced the growth signaling in the three cell lines. In contrast, the carboxy-terminal part of 98 amino acids strongly inhibited growth signaling in the two myeloid cell lines but not in BAF3 cells. Truncation of this region lead to an inability of the G-CSF-R to transduce maturation signals in L-GM cells. An alternative carboxy tail present in a splice variant of the G-CSF-R also inhibited growth signaling, notably in both the myeloid cells and BAF3 cells, but appeared not to be involved in maturation.

Purification, expansion, and multiple fluorochrome labeling of cord blood hemopoietic precursors: preliminary results

CD34-positive cells were isolated from a total of 23 cords using CellPro Ceprate columns. AIS MicroCellector flasks, and panning. The cells were (1) expanded in serum-free culture supplemented with a variety of combinations of cytokines and (2) immunophenotyped using multiple fluorochrome labeling. The results indicated that the avidin column produced the highest purity of CD34-positive cells, and that immature blast cells could be expanded in serum-free culture. Preliminary results suggested that the four fluorochrome labeling technique may provide useful information on the lineage commitment of cord blood precursor and blast cells.

Inhibition of the self-renewal capacity of blast progenitors from acute myeloblastic leukemia patients by site-selective 8-chloroadenosine 3',5'-cyclic monophosphate

The physiologic balance between the two regulatory subunit isoforms, RI and RII, of cAMP-dependent protein kinase is disrupted in cancer cells; growth arrest and differentiation of malignant cells can be achieved when the normal ratio of these intracellular signal transducers of cAMP is restored by the use of site-selective cAMP analogs. In this study we evaluated the effects of the site-selective cAMP analog 8-chloroadenosine 3',5'-cyclic monophosphate (8-Cl-cAMP) on clonogenic growth of blast progenitors from 15 patients with acute myeloblastic leukemia and 3 patients affected by advanced myelodysplastic syndrome. Leukemic blast progenitors undergo terminal divisions, giving rise to colonies in methylcellulose. The self-renewal capacity of blast progenitors is conversely reflected in a secondary methylcellulose assay after exponential growth of clonogenic cells in suspension cultures. In all the samples tested, 8-Cl-cAMP, at micromolar concentrations (0.1-50 microM), suppressed in a dose-dependent manner both primary colony formation in methylcellulose and the recovery of clonogenic cells from suspension culture. Strikingly, in the samples from the entire group of patients, 8-Cl-cAMP was more effective in inhibiting the self-renewing clonogenic cells than the terminally dividing blast cells (P = 0.005). In addition, in four out of six cases studied, 8-Cl-cAMP was able to induce a morphologic and/or immunophenotypic maturation of leukemic blasts. An evident reduction of RI levels in fresh leukemic cells after exposure to 8-Cl-cAMP was also detected. Our results showing that 8-Cl-cAMP is a powerful inhibitor of clonogenic growth of leukemic blast progenitors by primarily suppressing their self-renewal capacity indicate that this site-selective cAMP analog represents a promising biological agent for acute myeloblastic leukemia therapy in humans.

Capability of various cytokines to induce quiescent myeloid leukemia cells to the proliferative stage

In order to investigate the capability of cytokines to induce myeloid leukemia cells from G0 phase to the proliferative stage, blasts from 9 patients with AML and 1 patient with CML-MC were cultured with various cytokines (IL-3, GM-CSF, IL-3 + GM-CSF, G-CSF) for 48 hours or 96 hours in a serum-free culture system. Cells were analyzed by two-color flow cytometry, using PI and the monoclonal antibody Ki-67. The percentage of cells in G0 phase was reduced significantly when the cells were cultured with IL-3 (p < 0.01), GM-CSF (p < 0.01), and IL-3 + GM-CSF (p < 0.01) for 48 hours, as compared with the percentage of cells in G0 phase before culture. Moreover, the percentage of cells in S phase increased significantly when the cells were cultured with IL-3 (p < 0.01), GM-CSF (p < 0.02), and IL-3 + GM-CSF (p < 0.01) for 48 hours, as compared with the percentage of cells in S phase before culture. It is well known that many drugs which are widely used in the treatment of acute leukemia are cytotoxic mainly to proliferating cells, so that if quiescent G0 phase cells can be induced to the proliferative stage, the treatment of acute leukemia would become more effective. The present findings showed that a considerable variation was observed among individual patients in the induction of the G0 component to the proliferative stage.(ABSTRACT TRUNCATED AT 250 WORDS)

Primary human acute myeloblastic leukaemia: an analysis of in vitro granulocytic maturation following stimulation with retinoic acid and G-CSF

Acute myeloid leukaemia (AML) is characterized by the inability of myeloid cells to reach terminal maturation. We examined to what degree granulocytic maturation could be achieved by stimulating AML blast cells in an in vitro serum-free system with a combination of granulocyte-colony stimulating factor (G-CSF) and all-trans-retinoic acid (RA). Specimens from 41 AML patients were cultured for 7 d and then examined for cytochemistry (myeloperoxidase, Sudan Black, naphthyl-ASD-chloracetate esterase, periodic acid Schiff) an nitroblue tetrazolium reduction. The expression of CD11a, CD11b, CD11c, CD15, CD18, CD10, CD24 and B13-3 membrane antigens was also evaluated. Morphological and cytochemical studies were also performed after AML colony culture and culture of normal bone marrow cells (NBM). The comparative analysis of the panel of parameters was indicative of granulocytic maturation although to different degrees. The cells from 25/41 cases showed morphologic maturation (May-Grünwald-Giemsa). A positive correlation was evident between morphological maturation and CD11b expression (11/22 patients) as well as that of CD11c and CD15 (6 patients). Napthyl ASD chloroacetate esterase and PAS stainings also correlated with morphology (in 10/22 and 10/24 patients respectively). Nevertheless, the pattern of granulocytic maturation was remarkably variable among the 41 cases examined. The cells from only a few patients acquired the full spectrum of granulocytic markers. The comparison with normal bone marrow blasts indicates that serum-free culture conditions can, per se, limit granulocytic maturation, but it also confirms the intrinsic inability of AML cells to attain complete maturation in response to two potent granulocytic inducers.

Practical aspects and diagnostic significance of in vitro manipulation of progenitors in human acute myeloid and lymphoid leukaemia

Since their introduction in the early seventies, in vitro culture techniques for human acute leukaemia cells have been modified and improved considerably. Primarily, this is the result of the availability of the recombinant haematopoietic growth factors (HGFs). It is now possible to evaluate HGF responses of acute leukaemia cells in colony and DNA synthesis assays under fully defined conditions. In this chapter we summarize the current insights into the growth properties of human acute leukaemia progenitor cells and evaluate the potential significance of the application of in vitro clonogenic assays for refining the diagnosis of acute leukaemia, for detecting minimal residual disease and for monitoring therapy.

Tumor necrosis factor downregulates granulocyte-colony-stimulating factor receptor expression on human acute myeloid leukemia cells and granulocytes

Tumor necrosis factor (TNF) inhibits granulocyte-colony-stimulating factor (G-CSF)-induced human acute myeloid leukemia (AML) growth in vitro. Incubation of blasts from three patients with AML in serum-free medium with TNF (10(3) U/ml), and subsequent binding studies using 125I-G-CSF reveal that TNF downregulates the numbers of G-CSF receptors by approximately 70%. G-CSF receptor numbers on purified blood granulocytes are also downmodulated by TNF. Downregulation of G-CSF receptor expression becomes evident within 10 min after incubation of the cells with TNF at 37 degrees C and is not associated with an apparent change of the dissociation constant (Kd). The TNF effect does not occur at 0 degrees C and cannot be induced by IL-2, IL-6, or GM-CSF. TNF probably exerts its effect through activation of protein kinase C (PKC) as the TNF effect on G-CSF receptor levels can be mimicked by 12-O-tetradecanoylphorbol-13- acetate. The PKC inhibitor Staurosporine (Sigma Chemical Co., St. Louis, MO) as well as protease inhibitors can completely prevent G-CSF receptor downmodulation. Thus, it appears TNF may act as a regulator of G-CSF receptor expression in myeloid cells and shut off G-CSF dependent hematopoiesis. The regulatory ability of TNF may explain the antagonism between TNF and G-CSF stimulation.

Induction of granulocytic maturation in acute myeloid leukemia by G-CSF and retinoic acid

AML cells were cultured free of serum with G-CSF in combination with all-trans-retinoic acid (RA), prostaglandin E2 or 8-bromocyclic AMP to see whether the maturation blockade of these cells could be overcome. The combination G-CSF + RA was most effective in inducing morphologic maturation, i.e. in 7/10 cases. Morphological alterations in response to G-CSF + RA indicated progression of the cells along the granulocytic pathway towards metamyelocytes and granulocytes. However, morphologically mature AML cells remained negative for myeloperoxidase and Sudan black stainings, indicators of granulocytic maturation. Chloracetate esterase positivity and CD15 membrane antigens became expressed on cultured AML cells, i.e. on unstimulated and G-CSF/RA exposed blasts. Ingestion of latex beads and reduction of nitroblue tetrazolium salt occurred in cultured AML cells regardless of the presence of inducers. In almost all cases clonogenic cells persisted after exposure to G-CSF + RA suggesting that subpopulations of immature cells escaped the action of these inducers. Thus although G-CSF + RA were capable of inducing maturation of AML cells along the granulocytic lineage, maturation was incomplete and the effect was evident in a subfraction of the cells only.

Clonal growth and self-renewal of human myeloid leukemia cell lines (BRM and DD) in serum-free semi-solid culture

Primary and secondary colony formation of two new human myeloid leukemia cell lines (BRM and DD) were studied in serum-free semisolid cultures. The results indicate that bovine serum albumin and transferrin were essential for clonal growth in chemically defined medium. Insulin contributed only moderately beneficial effects. Initial cell density was also a major modulator of plating efficiency. Positive cooperation between the leukemia cells was shown by using autologous conditioned media. This is the first serum-free culture method that allows self-renewal of human myeloid leukemia cell lines in terms of secondary colony formation in methylcellulose cultures.

Susceptibility of acute myeloid leukemia (AML) cells from clinically resistant and sensitive patients to daunomycin (DNR): assessment in vitro after stimulation with colony stimulating factors (CSFs)

Chemosensitivity of purified AML blasts to daunomycin was examined under conditions of CSF stimulation and compared with clinical outcome of DNR combination chemotherapy. AML blasts from 16 patients were purified, incubated serum-free in the presence of optimal concentrations of a complete cocktail of IL-3, GM-CSF and G-CSF to provoke cell proliferation maximally, and DNR drug sensitivity in vitro was assessed by inhibition of DNA synthesis in response to titrated DNR concentrations. The sensitivity of proliferating AML cells to DNR did not correlate with the clinical response of the patients as identical dose-response curves were obtained for complete responders (n = 6), partial responders (n = 5) and resistant cases (n = 5). As a major part of the AML population was induced to enter DNA synthesis in vitro, these data suggest that the manoeuvre of cell cycle stimulation has abrogated cellular resistance to daunomycin and rendered in vivo, apparently refractory cells susceptible to the anthracycline.

Growth, differentiation and the beta-adrenergic signal system of HL-60 cells. Characterization in a medium with insulin as the only added protein

The purpose of the present investigation was to define experimental conditions for studies on growth, differentiation and the beta-adrenergic signal system of HL-60 cells. The cell medium was completely devoid of added proteins and hormones other than insulin. The HL-60 cell was able to grow and differentiate in this medium. The spontaneous differentiation along the granulocytic pathway after 72 hr, as assessed by the Nitro Blue tetrazolium test, increased by 400% compared to the serum supplemented medium, but the response to 1 microM retinoic acid was equal in the two media. Induction of monocytic differentiation by 0.16 microM phorbol-13-acetate-12-myristate, as determined by surface adherence after 24 hr, was lower in the absence than in the presence of serum. cAMP levels were elevated in response to (-)-isoproterenol. The EC50 was 0.36 +/- 0.01 microM (mean +/- SE, N = 3). The beta-adrenergic ligand 3H-CGP 12177 was specifically bound to 1 single class of binding sites (Kd: 0.15 +/- 0.04 nM, Bmax: 2220 +/- 150, mean +/- SE, N = 3). These data are comparable to our previously reported findings in serum supplemented medium. The present data show that HL-60 cells are able to grow and differentiate in the absence of serum proteins and hormones other than insulin. Under the present experimental conditions, these cells possessed functional beta-adrenergic receptors.

Maturation of human acute myeloid leukaemia in vitro: the response to five recombinant haematopoietic factors in a serum-free system

The abilities of human recombinant IL-3, GM-CSF, G-CSF, M-CSF and Epo to induce maturation in human AML cells in vitro were investigated using cell specimens from 25 AML patients. The experiments were carried out under exactly defined serum-free culture conditions. In the absence of CSFs, monocytic and/or granulocytic maturation was detected in 14/25 cases. IL-3, GM-CSF, G-CSF and M-CSF elevated the proportions of monocyte/macrophages in 3/25, 2/25, 1/25 and 6/25 cases respectively, and increased the percentages of mature granulocytes in 2/25, 1/25, 1/25 and 0/25 cases, and if so only to a limited extent (values below 50%). The 3H-thymidine (3H-TdR) uptake studies revealed that IL-3, GM-CSF, G-CSF and M-CSF were efficient stimulators of DNA synthesis of AML cells in 19, 15, 13 and four of those cases, respectively. Thus, although the cells in most cases responded to CSFs by activation of DNA synthesis, they were unable to give rise to terminally differentiated stages. Provision of CSFs in combination was more frequently effective in enhancing maturation and also increased the magnitude of maturation response. Monocytic versus granulocytic maturation of AML cells after culture did not correlate with the FAB cytology nor with the type of CSF presented; but generally granulocytic maturation was an infrequent phenomenon. Epo stimulated erythroid differentiation and DNA synthesis only in the case of erythroleukaemia, but it had no effect on the cells of 10 other AML cases. Extrapolation of these in vitro findings would suggest that CSFs would have a limited therapeutic utility to induce AML cell maturation in vivo and that hazards of stimulating blast cell proliferation with these factors may be anticipated.

Cell to cell contact enhances the proliferation of acute myeloid leukemia (AML) cells in vitro without an apparent role of adhesion glycoproteins LFA1, MAC1 and P150-95

Acute myeloblastic leukemia (AML) cells were cultured under conditions facilitating or preventing cell to cell contact. Proliferation of AML blasts of 24 patients was assessed in semisolid (containing 0.9% methylcellulose) and in liquid cultures, in which identical concentrations of colony stimulating factors (CSFs) had been provided. In all but one of the cases, significant DNA synthesis (evaluated by 3H-thymidine uptake) was observed when the cells were incubated in the liquid system, whereas in only 14 cases (58%), the cells were able to form clusters or colonies in the semisolid system. These findings suggest that AML cells from a large proportion of patients can proliferate only after stimulation with CSFs in a liquid system, i.e. when cultured under conditions permitting reciprocal contact between the cells. To establish further the importance of cell to cell contact for AML cell proliferation, cells from 19 patients were cultured in liquid medium concurrently in flat bottom microwells (in which a majority of the cells lie separate) and in round bottom microwells (in which cells show a tendency to aggregate). A significantly higher 3H-thymidine (TdR) incorporation in the round bottom cultures was observed in 15 out of 19 cases. The role of the leukocyte function antigens (LFA) LFA1, Mac1, P150-95 in this phenomenon was then analyzed, as these structurally related glycoproteins are involved in reactions requiring contact between hematopoietic cells. Membrane expression of the three antigens was first examined in 16 patients. LFA1, Mac1 and P150-95 were expressed on the AML cells of 15, 6 and 8 patients, respectively. Expression of these antigens did not change following short term incubation of the AML cells in the presence of CSFs. AML cells cultured in presence of saturating concentrations of monoclonal antibodies reacting with structures of these 3 antigens in order to abrogate their function did not suppress 3H-TdR uptake. Thus, no direct role for LFA1 and/or Mac1 and/or P150-95 antigens in mediating contact-induced AML proliferation could be demonstrated. It remains to be established which components are involved in the cell-cell contact-mediated upregulation of AML cell proliferation.

Proliferative response of highly purified B chronic lymphocytic leukemia cells in serum free culture to interleukin-2 and tumor necrosis factors alpha and beta

Recent studies have suggested that interleukin-2 (IL-2), tumor necrosis factor (TNF) and a crude preparation of B-cell growth factors (BCGF) have a regulatory role in the proliferation of B-CLL cells. However, interpretation of the experimental data has been complicated by potential methodological pitfalls. To establish the role of these factors in B-CLL growth, we investigated their stimulatory effects under accurately defined in vitro conditions. Purified B-CLL cells were obtained by fluorescence activated cell sorting on the basis of coexpression of CD5 and CD19/CD20/CD24 surface antigens in order to avoid interference of normal cell contamination. Subsequently, the cells were cultured free of serum. TNFs alpha and beta and BCGF induced DNA synthesis in the purified B-CLL cells in five out of six cases, as assessed by 3H-thymidine (TdR) uptake on days 3 and 6 of culture. The stimulating activity of BCGF could be suppressed by the addition of specific anti-TNF monoclonal antibodies, indicating that the BCGF activity had been, to a major extent, due to the presence of TNFs in this impure preparation. IL-2, when added as a single stimulus, induced DNA synthesis in the B-CLL cells in three out of six cases on day 3, but not on day 6 of culture. In some patients, cooperative effects of IL-2 and TNF were observed. Cytogenetic analysis was applied to confirm the CLL origin of the proliferating cells. The phorbol ester TPA or anti-IgM were not required for induction of DNA synthesis in the CLL cells, although TPA potentiated 3H-TdR uptake in three out of six cases, and anti-IgM in one case. Our data demonstrate that IL-2 and TNFs alpha and beta can act as growth factors for B-CLL cells under fully defined in vitro conditions, essentially without the need of TPA or anti-IgM as primary activation signals.