Epigenetic activation of O-linked β-N-acetylglucosamine transferase overrides the differentiation blockage in acute leukemia

Background

Overriding the differentiation blockage in acute myeloid leukemia (AML) is the most successful mode-of-action in leukemia therapy – now curing the vast majority of patients with acute promyelocytic leukemia (APL) using all-trans retinoic acid (ATRA)-based regimens. Similar approaches in other leukemia subtypes, such as IDH1/2-mutated AML, are under active investigation. We herein present successful release of the differentiation blockage upon treatment with the natural (−)-Δ⁹-Tetrahydrocannabinol isomer dronabinol in vitro and in vivo.

Methods

Cellular maturation and differentiation were followed in two patients employing whole genome methylation profiling, proteome analyses, NGS deep sequencing and multispectral imaging flow cytometry. For functional studies lentiviral OGT knock-down in vitro and ex vivo cell models were created to evaluate proliferative, apoptotic and differentiating effects of OGT in acute leukemia.

Findings

In here, we provide molecular evidence that dronbinol is capable to override the differentiation blockage of acute leukemia blasts at the state of the leukemia-initiating clone. We further identify the O-linked β-N-acetyl glucosamine (O-GlcNAc) transferase (OGT) to be crucial in this process. OGT is a master regulator enzyme adding O-GlcNAc to serine or threonine residues in a multitude of target proteins. Aberrant O-GlcNAc modification is implicated in pathologies of metabolic, neurodegenerative and autoimme diseases as well as cancers. We provide evidence that dronabinol induces transcription of OGT via epigenetic hypomethylation of the transcription start site (TSS). A lentiviral OGT-knock out approach proves the central role of OGT exerting antileukemic efficacy via a dual-mechanism of action: High concentrations of dronabinol result in induction of apoptosis, whereas lower concentrations drive cellular maturation. Most intriguingly, overriding of the differentiation blockage of acute leukemia blasts is validated in vivo following two patients treated with dronabinol.

Interpretation

In conclusion, we provide evidence for overcoming the differentiation blockage in acute leukemia in subentities beyond promyelocytic and IDH1/2-mutated leukemia and thereby identify O-GlcNAcylation as a novel (drugable) field for future leukemia research.

Funding

Unrestricted grant support by the IZKF Program of the Medical Faculty Tübingen (MMS) and Brigitte Schlieben-Lange Program as well as the Margarete von Wrangell Program of the Ministry of Science, Research and the Arts, Baden-Württemberg, Germany (KKS) and Athene Program of the excellence initiative University of Tübingen (KKS).

Human versus porcine mesenchymal stromal cells: phenotype, differentiation potential, immunomodulation and cardiac improvement after transplantation

Although mesenchymal stromal cells (MSCs) have been applied clinically to treat cardiac diseases, it is unclear how and to which extent transplanted MSCs exert their beneficial effects. To address these questions, pre-clinical MSC administrations are needed for which pigs appear to be the species of choice. This requires the use of porcine cells to prevent immune rejection. However, it is currently unknown to what extent porcine MSCs (pMSCs) resemble human MSCs (hMSCs). Aim of this study was to compare MSC from porcine bone marrow (BM) with human cells for phenotype, multi-lineage differentiation potential, immune-modulatory capacity and the effect on cardiac function after transplantation in a mouse model of myocardial infarction. Flow cytometric analysis revealed that pMSC expressed surface antigens also found on hMSC, including CD90, MSCA-1 (TNAP/W8B2 antigen), CD44, CD29 and SLA class I. Clonogenic outgrowth was significantly enriched following selection of CD271+ cells from BM of human and pig (129 ± 29 and 1961 ± 485 fold, respectively). hMSC and pMSC differentiated comparably into the adipogenic, osteogenic or chondrogenic lineages, although pMSC formed fat much faster than hMSC. Immuno-modulation, an important feature of hMSC, was clearly demonstrated for pMSC when co-cultured with porcine peripheral blood cells stimulated with PMA and pIL-2. Finally, pMSC transplantation after myocardial infarction attenuated adverse remodelling to a similar extent as hMSC when compared to control saline injection. These findings demonstrate that pMSCs have comparable characteristics and functionality with hMSCs, making reliable extrapolation of pre-clinical pMSC studies into a clinical setting very well possible.

Basic research and clinical applications of non-hematopoietic stem cells, 4-5 April 2008, Tubingen, Germany

From 4 to 5 April 2008, international experts met for the second time in Tubingen, Germany, to present and discuss the latest proceedings in research on non-hematopoietic stem cells (NHSC). This report presents issues of basic research including characterization, isolation, good manufacturing practice (GMP)-like production and imaging as well as clinical applications focusing on the regenerative and immunomodulatory capacities of NHSC.

Upregulation of frizzled 9 in astrocytomas

Wnt/frizzled (FZD) cascades play important roles in controlling cell fate, proliferation, migration, tissue architecture and organogenesis during embryonic development and in adult organisms. The potential involvement of this pathway in tumorigenesis has been established in several types of cancers. Frizzled 9 (FZD9) is expressed in brain and its aberrant expression in gastric cancer was observed. However, its association with astrocytomas remains unknown therefore we studied FZD9 expression in astrocytomas of different malignancy. In the present study, FZD9 expression in 25 astrocytomas was investigated using immunohistochemistry with specific antibodies. Further FZD9 expression in native human brain tissue and glioblastoma cell line were analysed using real-time reverse transcription polymerase chain reaction (RT-PCR). In human astrocytomas, FZD9 immunoreactivity (IR) was observed in both microvessels and neoplastic cells. The percentage of FZD9+ microvessels in relation to FZD9+ vessels was significantly higher in malignant astrocytomas than in low-grade astrocytomas and positively correlated with the astrocytoma World Health Organization (WHO) grading (r = 1, P = 0.04). Furthermore, the FZD9 IR scores positively correlated with astrocytoma WHO grading (r = 1, P = 0.04) and proliferating activity (r = 0.77, P < 0.001). Real-time RT-PCR data showed that FZD9 expression in human glioblastoma was significant higher than in normal brain (P < 0.05) but FZD9 expression was only slightly induced in cobalt chloride-treated human glioblastoma T98G cells compared with untreated cells (P > 0.05). FZD9 is upregulated in astrocytomas, suggesting that FZD9 could be important in the tumorigenesis of human astrocytomas.

The role of sialomucin CD164 (MGC-24v or endolyn) in prostate cancer metastasis

BACKGROUND

The chemokine stromal derived factor-1 (SDF-1 or CXCL12) and its receptor CXCR4 have been demonstrated to be crucial for the homing of stem cells and prostate cancers to the marrow. While screening prostate cancers for CXCL12-responsive adhesion molecules, we identified CD164 (MGC-24) as a potential regulator of homing. CD164 is known to function as a receptor that regulates stem cell localization to the bone marrow.

RESULTS

Using prostate cancer cell lines, it was demonstrated that CXCL12 induced both the expression of CD164 mRNA and protein. Functional studies demonstrated that blocking CD164 on prostate cancer cell lines reduced the ability of these cells to adhere to human bone marrow endothelial cells, and invade into extracellular matrices. Human tissue microarrays stained for CD164 demonstrated a positive correlation with prostate-specific antigen levels, while its expression was negatively correlated with the expression of androgen receptor.

CONCLUSION

Our findings suggest that CD164 may participate in the localization of prostate cancer cells to the marrow and is further evidence that tumor metastasis and hematopoietic stem cell trafficking may involve similar processes.

Hymenoptera-venom-induced upregulation of the basophil activation marker ecto-nucleotide pyrophosphatase/phosphodiesterase 3 in sensitized individuals

BACKGROUND

Bee and wasp venoms are potent allergens capable of inducing severe clinical reactions. To detect immediate-type hypersensitivity to these allergens, a rapid in vitro test was developed that relies on the upregulation of ecto-nucleotide pyrophosphatase/phosphodiesterase 3 (E-NPP3) on activated basophils.

METHODS

Blood basophils of 13 healthy donors and 22 patients allergic to bee or wasp venom were analyzed for E-NPP3 (CD203c) expression using monoclonal antibody 97A6. Basophils were analyzed by flow cytometry after activation with anti-IgE antibody or allergen. Venom-induced E-NPP3 upregulation on basophils was compared with diagnostic parameters, including skin tests and assessment of specific IgE. In selected samples, the increase in E-NPP3 expression on activated basophils was compared with histamine release and CD63 upregulation.

RESULTS

In 20/22 patients sensitized to wasp or bee venom, E-NPP3 expression on basophils was upregulated in response to activation by allergen or anti-IgE. The maximum increase in E-NPP3 expression (above ten times of baseline) was achieved after 15 min of stimulation with 1 microg/ml of allergen or anti-IgE antibody. Sensitized individuals who failed to upregulate E-NPP3 in response to IgE receptor cross-linking also failed to induce histamine release and CD63 upregulation.

CONCLUSIONS

Flow cytometric determination of hymenoptera-venom-induced upregulation of E-NPP3 is a novel in vitro test to identify sensitized individuals.

Quantitative, phenotypic, and functional evaluation of basophils in myelodysplastic syndromes

BACKGROUND

The myelodysplastic syndromes (MDS) are a group of clonal haematological disorders characterized by cytopenia(s), reduced differentiation-capacity of myeloid cells, and impaired leukocyte function. However, little is known so far about basophil granulocytes in MDS.

DESIGN

We have compared the numbers, phenotype and function of basophils in MDS patients with those in healthy subjects. A total numer of 23 patients with MDS (refractory anaemia, n = 8; refractory anaemia with ringsideroblasts, n = 7; refractory anaemia with excess of blasts/refractory anaemia with excess of blasts in transformation, n = 8) and 20 healthy donors were included.

RESULTS

The numbers of blood basophils in MDS patients (34.6 +/- 62.9 microL-1) was lower compared to healthy controls (58.6 +/- 64.9 microL-1). Correspondingly, whole blood histamine levels were lower in MDS patients (MDS 34.1 +/- 29.1 ng mL-1 vs. normal donors 72.0 +/- 36.9 ng mL-1). Like "normal" basophils, basophils in MDS expressed interleukin-3 receptor alpha (CD123), E-NPP3 (CD203c), CR1 (CD35), CR3 (CD11b), CR4 (CD11c), membrane co-factor protein (CD46), decay-accelerating factor (CD55) and membrane attack complex inhibitory factor (CD59), as well as receptors for C3a, C5a (CD88), and IgE. Recombinant human (rh) C5a and anti-IgE induced significant release of histamine from basophils in both groups of donors without significant differences between MDS and healthy controls.

CONCLUSIONS

The absolute numbers of basophils in MDS patients are lower than in normal donors. However, basophils in MDS do not differ from their "normal counterparts" in terms of complement receptor expression, IgE-receptor expression, or functional responses to respective ligands.

The epithelial tumor antigen MUC1 is expressed in hematological malignancies and is recognized by MUC1-specific cytotoxic T-lymphocytes

The epithelial mucin MUC1 is overexpressed on the cell surface of many epithelial malignancies as well as on some B-cell lymphomas and multiple myelomas. Recently, we identified two HLA-A2-restricted T-cell epitopes derived from the MUC1 protein. To further extend the potential application of these peptides, we analyzed the expression of MUC1 on blast cells from patients with acute myelogenous leukemia (AML; n = 43) and several other hematological malignancies including acute lymphoblastic leukemia (n = 24), chronic lymphocytic leukemia (n = 36), hairy cell leukemia (n = 9), follicular lymphoma (n = 7), and multiple myeloma (n = 12). Using reverse transcription-PCR and MUC1-specific monoclonal antibodies, MUC1 expression was found in 67% of AML samples and 92% of myeloma samples. To analyze the presentation of MUC1 peptides by primary AML blasts, we induced MUC1-specific CTLs in vitro using peptide-pulsed dendritic cells from HLA-A2+ healthy donors as antigen-presenting cells. These CTLs efficiently lysed in an antigen-specific and HLA-A2-restricted manner not only target cells pulsed with the antigenic peptide but also tumor cell lines including multiple myeloma cells and primary AML blasts that constitutively expressed both MUC1 and HLA-A2. The specificity of the CTLs was confirmed in a cold target inhibition assay. Our data demonstrate that MUC1-derived peptides are tumor antigens in AML and several other hematological malignancies that could potentially be used for immunotherapeutic approaches.

The monoclonal antibody W7C5 defines a novel surface antigen on hematopoietic stem cells

We recently raised a monoclonal antibody, termed W7C5, against a surface antigen that is expressed at low levels on bone marrow and peripheral blood CD34+ stem/progenitor cells but at high levels on fetal liver CD34+ cells. A reasonable staining intensity was achieved using magnetofluorescent liposome conjugates to analyze expression of W7C5 antigen on CD34+CD38- bone marrow (BM) cells. Flow cytometric analyses revealed that W7C5 detects about 50% of immature CD34+CD38- BM cells that coexpressed the differentiation antigens CD164, CD133, and CD172a (SIRP alpha). In addition, W7C5 also recognized a CD34- BM fraction. These cells were negative for CD117 and CD133, but expressed CD45 and moderate levels of CD164. Injection of selected CD34+W7C5+ and CD34-W7C5+ cells into 55-60-day-old fetal sheep resulted in an engraftment of both fractions. Partial amino acid sequence analysis of affinity-purified lysates of KU-812 cells revealed that W7C5 detects a novel membrane protein. Together, W7C5 defines a novel molecule that is expressed on CD34+ as well as on CD34- stem cell subsets.

Dendritic cell-based vaccines in patients with hematological malignancies

The epithelial mucin MUC1 is overexpressed on many epithelial malignancies as well as on some B-cell lymphomas and multiple myelomas. In the present study, we described MUC1 expression also on primary AML blasts. To analyze the presentation of MUC1-derived HLA-A2 restricted peptides by primary AML blasts, we induced MUC1-specific cytotoxic T-lymphocytes (CTLs) in vitro using peptide pulsed dendritic cells from HLA-A2+ healthy donors as antigen-presenting cells. These CTLs efficiently lysed primary AML blasts that constitutively expressed both MUC1 and HLA-A2. The specificity of the CTLs was confirmed in a cold target inhibition assay. Our data demonstrate that MUC1-derived peptides are tumor antigens in AML which could potentially be used for immunotherapeutic approaches.

The basophil activation marker defined by antibody 97A6 is identical to the ectonucleotide pyrophosphatase/phosphodiesterase 3

It has recently been shown that monoclonal antibody (MoAb) 97A6 detects a surface antigen expressed on basophils and their CD34(+) precursor cells, as well as the basophil cell line KU-812. In this report the partial amino acid sequence of affinity chromatography- and sodium dodecyl sulfate-polyacrylamide gel electrophoresis-separated 97A6 antigen(s) from KU-812 lysates was determined. Sequence alignment of high-performance liquid chromatography-selected tryptic peptides from the resulting 130- and 150-kd bands revealed a 100% identity with amino acids 393 to 405 of ectonucleotide pyrophosphatase/phosphodiesterase-3 (E-NPP3; CD203c) but not of the related ectoenzyme PC-1 (E-NPP1). Moreover, MoAb 97A6 selectively recognized 293 cells transfected with human E-NPP3, but did not react with cells transfected with PC-1 or parental 293 cells. In addition, E-NPP3 messenger RNA expression was detected in basophils but not other peripheral blood cells. Finally, MoAb 97A6 immunoprecipitated phosphodiesterase activity from KU-812 cells and peripheral blood basophils, but not from other cell populations. These data demonstrate that MoAb 97A6 recognizes the functionally active type II transmembrane ectoenzyme E-NPP3.

Signal-regulatory protein alpha (SIRPalpha) but not SIRPbeta is involved in T-cell activation, binds to CD47 with high affinity, and is expressed on immature CD34(+)CD38(-) hematopoietic cells

Signal-regulatory proteins (SIRPs) represent a new family of inhibitory/activating receptor pairs. They consist of 3 highly homologous immunoglobulin (Ig)-like domains in their extracellular regions, but differ in their cytoplasmic regions by the presence (SIRPalpha) or absence (SIRPbeta) of immunoreceptor tyrosine-based inhibitory motifs (ITIMs). To analyze the differential expression on hematopoietic cells, function and ligand binding capacity of SIRPalpha and SIRPbeta molecules, soluble fusion proteins consisting of the extracellular domains of SIRPalpha1, SIRPalpha2, and SIRPbeta1, as well as SIRPalpha/beta-specific and SIRPbeta-specific monoclonal antibodies (MoAbs) were generated. In contrast to SIRPalpha1 and SIRPalpha2, no adhesion of SIRPbeta1 to CD47 could be detected by cell attachment assays and flow cytometry. Using deletion constructs of SIRPalpha1, the epitope responsible for SIRPalpha1 binding to CD47 could be confined to the N-terminal Ig-like loop. Flow cytometry analysis with SIRPalpha/beta- and SIRPbeta-specific MoAbs revealed that SIRPalpha but not SIRPbeta is expressed on CD34(+)CD38(-) hematopoietic cells. In addition, a strong SIRPalpha expression was also observed on primary myeloid dendritic cells (DCs) from peripheral blood as well as on in vitro generated DCs. Analysis of the T-cell stimulatory capacity of in vitro generated DCs in the presence of soluble SIRPalpha1 fusion proteins as well as SIRPalpha/beta-specific and CD47-specific MoAbs revealed a significant reduction of T-cell proliferation in mixed lymphocyte reaction and inhibition of induction of primary T-cell responses under these conditions. In contrast, soluble SIRPalpha or SIRPbeta-specific antibodies had no effect. The data suggest that the interaction of SIRPalpha with CD47 plays an important role during T-cell activation and induction of antigen-specific cytotoxic T-lymphocyte responses by DCs.

Immunohistochemical properties of bone marrow mast cells in systemic mastocytosis: evidence for expression of CD2, CD117/Kit, and bcl-x(L)

In an attempt to identify novel diagnostic markers for mast cell (MC)-proliferative disorders, serial bone marrow (bm) sections of 22 patients with mastocytosis (systemic indolent mastocytosis, n = 19; mast cell leukemia [MCL], n = 1; isolated bm mastocytosis, n = 2) were analyzed by immunohistochemistry using antibodies against CD2, CD15, CD29, CD30, CD31, CD34, CD45, CD51, CD56, CD68R, CD117, HLA-DR, bcl-2, bcl-x(L), myeloperoxidase (MPO), and tryptase. Staining results revealed expression of bcl-x(L), CD68R, and tryptase in neoplastic MCs (focal dense infiltrates) in all patients. Mastocytosis infiltrates were also immunoreactive for CD45, CD117 (Kit), and HLA-DR. In most cases, the CD2 antibody produced reactivity with bm MCs in mastocytosis, whereas in control cases (reactive bm, immunocytoma, myelodysplastic syndrome), MCs were consistently CD2 negative. Expression of bcl-2 was detectable in a subset of MCs in the patient with MCL, whereas no reactivity was seen in patients with SIM or bm mastocytosis. Mastocytosis infiltrates did not react with antibodies against CD15, CD30, CD31, CD34, or MPO. In summary, our data confirm the diagnostic value of staining for tryptase, Kit, and CD68R in mastocytosis. Apart from these, CD2 may be a novel useful marker because MCs in mastocytosis frequently express this antigen, whereas MCs in other pathologic conditions are CD2 negative.

Cutting edge: characterization of allorestricted and peptide-selective alloreactive T cells using HLA-tetramer selection

The vast majority of alloreactive T cells recognize foreign MHC molecules in a peptide-dependent manner. A subpopulation of these peptide-dependent alloreactive T cells is peptide-specific and contains T cells that are of interest for tumor immunotherapy. Allorestricted T cells (i.e., peptide-specific and alloreactive) specific for tumor-associated Ags can be raised in vitro. However, it is technically difficult to distinguish between peptide-specific and peptide-nonspecific alloreactive T cells by functional assays in vitro. Here we show for the first time that allorestricted T cells specifically bind HLA-peptide tetrameric complexes, as nominal Ag-specific T cells would do. In consequence, fluorescent HLA-peptide tetrameric complexes can be used for sorting and cloning of allorestricted CTLs specific for a peptide of interest. We also show by the mean of HLA-peptide tetramers the existence of peptide-selective alloreactive T cells that recognize a conformation on the foreign-MHC brought about by some but not all peptides bound.

Variable expression of activation-linked surface antigens on human mast cells in health and disease

Mast cells (MC) are multipotent effector cells of the immune system. They contain an array of biologically active mediator substances in their granules. MC also express a number of functionally important cell surface antigens, including stem cell factor receptor (SCFR=kit=CD117), high affinity IgER (FcepsilonRI), or CSaR (CD88). Respective ligands can induce or promote degranulation, migration, or cytokine production. Other integral surface molecules can mediate adhesion or cell aggregation. Recent data suggest that a number of critical molecules are variably expressed on the surface of human MC. In fact, depending on the environment (organ), stage of cell maturation, type of disease, and other factors, MC express variable amounts of activation-linked antigens (CD25, CD63, CD69, CD88), cell recognition molecules (CD2, CD11, CD18, CD50, CD54), or cytokine receptors. At present, however, little is known about the mechanisms and regulation of expression of such antigens. The present article gives an overview of MC phenotypes in health and disease, and attempts to provide explanations for the phenotypic variability of MC.

Association of signal-regulatory proteins beta with KARAP/DAP-12

The signal-regulatory proteins (SIRP) are Ig-like cell surface receptors detected in hematopoietic and non-hematopoietic cells. SIRP are classified as SIRPalpha molecules, containing a 110- to 113-amino acid long, or SIRPbeta molecules, with a 5-amino acid long intracytoplasmic domain. SIRPalpha molecules belong to inhibitory immunoreceptor tyrosine-based inhibition motif (ITIM)-bearing molecules. The majority of ITIM-bearing receptors are paired with activating isoforms, which share highly related extracytoplasmic domains but harbor a shorter cytoplasmic domain devoid of ITIM and contain a charged amino acid residue in their transmembrane domain. Activating receptors are associated with immunoreceptor tyrosine-based activation motif (ITAM)-bearing proteins, such as KARAP/DAP-12 and FcRgamma. In this report, we show that human SIRPbeta1 is included in an oligomeric complex with KARAP/DAP-12 in hematopoietic and non-hematopoietic transfectant cells as well as in human monocytes. The physical association between SIRPbeta1 and KARAP/DAP-12 results in the functional coupling of SIRPbeta1 engagement to the recruitment of the protein tyrosine kinase Syk and to serotonin release in RBL cell transfectants. Therefore our results show that SIRPbeta1 acts as an activating isoform of SIRPalpha molecules, confirming the co-existence of inhibitory ITIM-bearing molecules, recruiting SHP-1 and SHP-2 protein tyrosine phosphatases, and activating counterparts, whose engagement couples to protein tyrosine kinases via ITAM-bearing molecules.

CD164 monoclonal antibodies that block hemopoietic progenitor cell adhesion and proliferation interact with the first mucin domain of the CD164 receptor

The novel sialomucin, CD164, functions as both an adhesion receptor on human CD34+ cell subsets in bone marrow and as a potent negative regulator of CD34+ hemopoietic progenitor cell proliferation. These diverse effects are mediated by at least two functional epitopes defined by the mAbs, 103B2/9E10 and 105A5. We report here the precise epitope mapping of these mAbs together with that of two other CD164 mAbs, N6B6 and 67D2. Using newly defined CD164 splice variants and a set of soluble recombinant chimeric proteins encoded by exons 1-6 of the CD164 gene, we demonstrate that the 105A5 and 103B2/9E10 functional epitopes map to distinct glycosylated regions within the first mucin domain of CD164. The N6B6 and 67D2 mAbs, in contrast, recognize closely associated and complex epitopes that rely on the conformational integrity of the CD164 molecule and encompass the cysteine-rich regions encoded by exons 2 and 3. On the basis of their sensitivities to reducing agents and to sialidase, O-sialoglycoprotease, and N-glycanase treatments, we have characterized CD164 epitopes and grouped them into three classes by analogy with CD34 epitope classification. The class I 105A5 epitope is sialidase, O-glycosidase, and O-sialoglycoprotease sensitive; the class II 103B2/9E10 epitope is N-glycanase, O-glycosidase, and O-sialoglycoprotease sensitive; and the class III N6B6 and 67D2 epitopes are not removed by such enzyme treatments. Collectively, this study indicates that the previously observed differential expression of CD164 epitopes in adult tissues is linked with cell type specific post-translational modifications and suggests a role for epitope-associated carbohydrate structures in CD164 function.

Functionally defined CD164 epitopes are expressed on CD34(+) cells throughout ontogeny but display distinct distribution patterns in adult hematopoietic and nonhematopoietic tissues

Three distinct classes of epitopes on human CD164 have been identified. Two of these, recognized by the monoclonal antibodies 105A5 and 103B2/9E10, are the CD164 class I and class II functionally defined epitopes, which cooperate to regulate adhesion and proliferation of CD34(+) cell subsets. In this article, we demonstrate that these 2 CD164 epitopes are expressed on CD34(+) cells throughout ontogeny, in particular on CD34(+ )cell clusters associated with the ventral floor of the dorsal aorta in the developing embryo and on CD34(+) hematopoietic precursor cells in fetal liver, cord blood, and adult bone marrow. While higher levels of expression of these CD164 epitopes occur on the more primitive AC133(hi)CD34(hi)CD38(lo/-) cell population, they also occur on most cord blood Lin(-)CD34(lo/-)CD38(lo/- )cells, which are potential precursors for the AC133(hi)CD34(hi)CD38(lo/-) subset. In direct contrast to these common patterns of expression on hematopoietic precursor cells, notable differences in expression of the CD164 epitopes were observed in postnatal lymphoid and nonhematopoietic tissues, with the class I and class II CD164 epitopes generally exhibiting differential and often reciprocal cellular distribution patterns. This is particularly striking in the colon, where infiltrating lymphoid cells are CD164 class I-positive but class II-negative, while epithelia are weakly CD164 class II-positive. Similarly, in certain lymphoid tissues, high endothelial venules and basal and subcapsular epithelia are CD164 class II-positive, while lymphoid cells are CD164 class I-positive. It therefore seems highly likely that these CD164 class I and II epitopes will mediate reciprocal homing functions in these tissue types.

Effective ex vivo generation of granulopoietic postprogenitor cells from mobilized peripheral blood CD34(+) cells

OBJECTIVE

Neutropenia following high-dose chemotherapy and peripheral blood progenitor cell (PBPC) transplantation might be abrogated by an additional transplantation of ex vivo generated granulopoietic postprogenitor cells (GPPC). Therefore, the ex vivo expansion of CD34(+) PBPC was systematically studied aiming for optimum GPPC production.

MATERIALS AND METHODS

CD34(+) PBPC were cultured in serum-free medium comparing different (n = 32) combinations of stem cell factor (S), interleukin 1 (1), interleukin 3 (IL-3) (3), interleukin-6 (6), erythropoietin (E), granulocyte colony-stimulating factor (G), granulate-macrophage colony-stimulating factor (GM), daniplestim (D, a novel IL-3 receptor agonist), and Flt3 ligand (FL) under various culture conditions. Ex vivo generated cells were assessed by flow cytometry, morphology, and progenitor cell assays.

RESULTS

Addition of G +/- GM but not GM alone to cultures stimulated with S163E effectively induced the generation of GPPC. GPPC production was maximum after 12 to 14 days. Best expansion rates were observed when cells were cultured at 1.5x10(4)/mL in 21% O(2). Modifications of culture conditions were either less or equally effective (i.e., modification of starting cell concentrations, low oxygen, addition of serum albumin or autologous plasma, repetitive feeding). Comparison of different cytokine combinations revealed that the optimum GPPC expansion cocktail consisted of S6GD+FL (day 12: 130-fold cellular expansion, 32% myeloblasts/promyelocytes, 49.4% myelocytes/metamyelocytes, 12.4% bands/segmented), which furthermore expanded CD34(+) cells (3.4-fold) and clonogenic progenitors (13.4-fold).

CONCLUSION

Using the S6DG+FL expansion cocktail, GPPC could be effectively produced ex vivo starting from positively selected CD34 PBPC, possibly enabling amelioration or even abrogation of posttransplant neutropenia.

Effective ex vivo generation of megakaryocytic cells from mobilized peripheral blood CD34(+) cells with stem cell factor and promegapoietin

OBJECTIVE

The additional transplantation of ex vivo-generated megakaryocytic cells might enable the clinician to ameliorate or abrogate high-dose chemotherapy-induced thrombocytopenia. Therefore, the ex vivo expansion of CD34(+) PBPC was systematically studied aiming for an optimum production of megakaryocytic cells.

MATERIALS AND METHODS

CD34(+) PBPC were cultured in serum-free medium comparing different (n = 23) combinations of stem cell factor (SCF) (S), IL-1beta (1), IL-3 (3), IL-6 (6), erythropoietin (EPO) (E), thrombopoietin (TPO) (T) and promegapoietin (PMP, a novel chimeric IL-3/TPO receptor agonist). Ex vivo-generated cells were assessed by flow cytometry, morphology, and progenitor cell assays.

RESULTS

Addition of TPO to cultures stimulated with S163E, a potent progenitor cell expansion cocktail previously described by our group, effectively induced the generation of CD61(+) cells (day 12: 31.4 +/- 7.9%). The addition of PMP tended to be more effective than TPO +/- IL-3. Whereas EPO was not required to maximize TPO- or PMP-induced megakaryocytic cell production, the use of IL-6 and IL-1beta augmented cellular expansion as well as CD61(+) cell production rates in the majority of cytokine combinations studied. Thus, the most effective CD61(+) cell expansion cocktail consisted of S163 + PMP which resulted in 65.9 +/- 3.0% CD61(+) at day 12 and an overall production of 40.7 +/- 4.5 CD61(+) cells per seeded CD34(+) PBPC. However, the basic 2-factor combination S + PMP also allowed for an effective CD61(+) cell production (day 12 CD61(+) cell production: 15.1 +/- 1.6). Moreover, maximum amplification of CFU-Meg was observed after 7 days using this two-factor cocktail (12.9 +/- 2.6-fold). The majority of CD61(+) cells generated in TPO- or PMP-based medium were low-ploidy 4N and 8N cells, and ex vivo-generated CD61(+), CD41(+), and CD42b(+) cells were mainly double positive for FACS-measured intracellular von Willebrand Factor (vWF) (76.7 +/- 3.3%, 58.8 +/- 4.4%, and 82.7 +/- 2.5%, respectively).

CONCLUSIONS

Taken together, this study demonstrates that megakaryocytic cells can be effectively produced ex vivo with as little as two-factors (SCF + PMP), an approach that might be favorably employed in a clinical expansion trial aiming to ameliorate high-dose chemotherapy-induced thrombocytopenia.

Cutting edge: signal-regulatory protein beta 1 is a DAP12-associated activating receptor expressed in myeloid cells

Signal-regulatory proteins (SIRPs) are cell-surface glycoproteins expressed on myeloid and neural cells that have been shown to recruit SH2 domain-containing protein phosphatase 1 (SHP-1) and SHP-2 and to regulate receptor tyrosine kinase-coupled signaling. One SIRP of unknown function, designated SIRP beta 1, contains a short cytoplasmic domain that lacks sequence motifs capable of recruiting SHP-1 and SHP-2. Using a SIRP-specific mAb, we show that SIRP beta 1 is expressed in monocytes and dendritic cells and associates with the signal transduction molecule DAP12. SIRP beta 1/DAP12 complex formation was required for efficient cell-surface expression of SIRP beta 1. Stimulation of this complex induced tyrosine phosphorylation, mitogen-activated protein kinase activation, and cellular activation. Thus, SIRP beta 1 is a new DAP12-associated receptor involved in the activation of myeloid cells.

Ex vivo manipulation of hematopoietic stem and progenitor cells

Ex vivo manipulations of hematopoietic stem and progenitor cells are Increasingly used in the context of autologous and allogeneic stem-cell transplantation. These manipulations include the positive selection of CD34+ cells for tumor-cell reduction and/or T-cell depletion, the ex vivo expansion of hematopoietic progenitor and stem cells under appropriate cytokine-stimulated culture conditions, and the ex vivo generation of myeloid or megakaryocytic postprogenitor cells and Immune effector cells. This article summarizes both the preclinical data on the ex vivo expansion of hematopoietic progenitor and stem cells from purified CD34+ cells and the Initial clinical studies with ex vivo-expanded stem and progenitor cells for hematopoietic support after high-dose chemotherapy.

Human signal-regulatory protein is expressed on normal, but not on subsets of leukemic myeloid cells and mediates cellular adhesion involving its counterreceptor CD47

Signal-regulatory proteins (SIRPs) comprise a novel transmembrane glycoprotein family involved in the negative regulation of receptor tyrosine kinase-coupled signaling pathways. To analyze the expression and function of SIRPs, we prepared soluble recombinant fusion proteins of the extracellular regions of SIRPalpha1 and SIRPalpha2, as well as a variety of monoclonal antibodies (MoAbs) against these domains. The antibodies reacted predominantly with monocytes, granulocytes, dendritic cells, and their precursors, as well as with bone marrow CD34(+), AC133(+), CD90(+) hematopoietic stem/progenitor cells. In contrast, SIRP expression was absent or significantly reduced on the majority of myeloid blasts from patients with acute myeloid leukemia (AML) or chronic myeloid leukemia (CML). Functional studies showed that the extracellular domains of SIRPalpha1 and SIRPalpha2 support adhesion of a number of primary hematopoietic cells and cell lines. This interaction could be blocked by 4 of 7 SIRPalpha1-reactive MoAbs. In addition, SIRPalpha1 and SIRPalpha2 competed for the same cell binding site, suggesting a common widely expressed SIRP ligand. In an approach to identify this molecule, MoAbs were generated against the SIRP-binding cell line CCRF-CEM, and MoAb CC2C6 was selected because of its capacity to inhibit cell binding to SIRPalpha1. Further analysis showed that this antibody recognized CD47, a ubiquitously expressed plasma membrane protein previously implicated in integrin function, host defense action, and neutrophil migration. In this study, we identify CD47 as the extracellular ligand for human SIRP and show that these two counterreceptors are involved in cellular adhesion.

The monoclonal antibody 97A6 defines a novel surface antigen expressed on human basophils and their multipotent and unipotent progenitors

Basophils (Ba) and mast cells (MC) are important effector cells of inflammatory reactions. Both cell types derive from CD34(+) hematopoietic progenitors. However, little is known about the cell subsets that become committed to and give rise to Ba and/or MC. We have generated a monoclonal antibody (MoAb), 97A6, that specifically detects human Ba, MC (lung, skin), and their CD34(+) progenitors. Other mature hematopoietic cells (neutrophils, eosinophils, monocytes, lymphocytes, platelets) did not react with MoAb 97A6, and sorting of 97A6(+) peripheral blood (PB) and bone marrow (BM) cells resulted in an almost pure population (>98%) of Ba. Approximately 1% of CD34(+) BM and PB cells was found to be 97A6(+). Culture of sorted CD34(+)97A6(+) BM cells in semisolid medium containing phytohemagglutinin-stimulated leukocyte supernatant for 16 days (multilineage assay) resulted in the formation of pure Ba colonies (10 of 40), Ba-eosinophil colonies (7 of 40), Ba-macrophage colonies (3 of 40), and multilineage Ba-eosinophil-macrophage and/or neutrophil colonies (12 of 40). In contrast, no Ba could be cultured from CD34(+)97A6(-) cells. Liquid culture of CD34(+) PB cells in the presence of 100 ng/mL interleukin (IL)-3 (Ba progenitor assay) resulted in an increase of 97A6(+) cells, starting from 1% of day-0 cells to almost 70% (basophils) after day 7. Culture of sorted BM CD34(+)97A6(+) cells in the presence of 100 ng/mL stem cell factor (SCF) for 35 days (mast cell progenitor assay) resulted in the growth of MC (>30% on day 35). Anti-IgE-induced IgE receptor cross-linking on Ba for 15 minutes resulted in a 4-fold to 5-fold upregulation of 97A6 antigen expression. These data show that the 97A6-reactive antigen plays a role in basophil activation and is expressed on multipotent CD34(+) progenitors, MC progenitors, Ba progenitors, as well as on mature Ba and tissue MC. The lineage-specificity of MoAb 97A6 suggests that this novel marker may be a useful tool to isolate and analyze Ba/MC and their progenitors.

Unicellular-unilineage erythropoietic cultures: molecular analysis of regulatory gene expression at sibling cell level

In vitro studies on hematopoietic control mechanisms have been hampered by the heterogeneity of the analyzed cell populations, ie, lack of lineage specificity and developmental stage homogeneity of progenitor/precursor cells growing in culture. We developed unicellular culture systems for unilineage differentiation of purified hematopoietic progenitor cells followed by daughter cell analysis at cellular and molecular level. In the culture system reported here, (1) the growth factor (GF) stimulus induces cord blood (CB) progenitor cells to proliferate and differentiate/mature exclusively along the erythroid lineage; (2) this erythropoietic wave is characterized by less than 4% apoptotic cells; (3) asymmetric divisions are virtually absent, ie, nonresponsive hematopoietic progenitors with no erythropoietic potential are forced into apoptosis; (4) the system is cell division controlled (cdc), ie, the number of divisions performed by each cell is monitored. Single-cell reverse transcriptase-polymerase chain reaction (RT-PCR) analysis was applied to this culture system to investigate gene expression of diverse receptors, markers of differentiation, and transcription factors (EKLF, GATA-1, GATA-2, p45 NF-E2, PU.1, and SCL/Tal1) at discrete stages of erythropoietic development. Freshly isolated CD34(+) cells expressed CD34, c-kit, PU.1, and GATA-2 but did not express CD36, erythropoietin receptor (EpoR), SCL/Tal1, EKLF, NF-E2, GATA-1, or glyocophorin A (GPA). In early to intermediate stages of erythroid differentiation we monitored the induction of CD36, Tal1, EKLF, NF-E2, and GATA-1 that preceeded expression of EpoR. In late stages of erythroid maturation, GPA was upregulated, whereas CD34, c-kit, PU.1, and GATA-2 were barely or not detected. In addition, competitive single-cell RT-PCR was used to assay CD34 mRNA transcripts in sibling CD34(+)CD38(-) cells differentiating in unilineage erythroid cultures: this analysis allowed us to semiquantitate the gradual downmodulation of CD34 mRNA from progenitor cells through their differentiating erythroid progeny. It is concluded that this novel culture system, coupled with single-cell RT-PCR analysis, may eliminate the ambiguities intrinsic to molecular studies on heterogeneous populations of hematopoietic progenitors/precursors growing in culture, particularly in the initial stages of development.

Expression of MUC-1 epitopes on normal bone marrow: implications for the detection of micrometastatic tumor cells

PURPOSE

The expression of the carcinoma-associated mucin MUC-1 is thought to be restricted to epithelial cells and is used for micrometastatic tumor cell detection in patients with solid tumors, including those with breast cancer. Little is known, however, about the expression of MUC-1 epitopes in normal hematopoietic cells.

MATERIALS AND METHODS

MUC-1 expression was analyzed by flow cytometry and immunocytology on bone marrow (BM) mononuclear cells and purified CD34+ cells from healthy volunteers, using different anti-MUC-1-specific monoclonal antibodies. In addition, Western blotting of MUC-1 proteins was performed.

RESULTS

Surprisingly, 2% to 10% of normal human BM mononuclear cells expressed MUC-1, as defined by the anti-MUC-1 antibodies BM-2 (2E11), BM-7, 12H12, MAM-6, and HMFG-1. In contrast, two antibodies recognizing the BM-8 and the HMFG-2 epitopes of MUC-1 were not detected. MUC-1+ cells from normal BM consisted primarily of erythroblasts and normoblasts. In agreement with this, normal CD34+ cells cultured in vitro to differentiate into the erythroid lineage showed a strong MUC-1 expression on day 7 proerythroblasts. Western blotting of these cells confirmed that the reactive species is the known high molecular weight MUC-1 protein.

CONCLUSION

Our data demonstrate that some MUC-1 epitopes are expressed on normal BM cells and particularly on cells of the erythroid lineage. Hence the application of anti-MUC-1 antibodies for disseminated tumor cell detection in BM or peripheral blood progenitor cells may provide false-positive results, and only carefully evaluated anti-MUC-1 antibodies (eg, HMFG-2) might be selected. Furthermore, MUC-1-targeted immunotherapy in cancer patients might be hampered by the suppression of erythropoiesis.

Characterization of purified and ex vivo manipulated human hematopoietic progenitor and stem cells in xenograft recipients

Research on the biology, regulation, and transplantation of human hematopoietic stem cells requires test systems for the detection, monitoring, and quantitation of these cells. Xenografted animal models provide suitable stem cell assays, since they allow long-term engraftment, multilineage differentiation, and serial transfer of human hematopoietic cells. Recent techniques for the separation of hematopoietic cells have provided highly purified cellular subsets selected on the basis of the surface marker phenotype. The stem cell content of these subsets, however, is still unclear. Also, innovative approaches for the induction of hematopoietic cell proliferation and differentiation have generated ex vivo manipulated cells whose biological properties and functions still remain to be assessed. This paper reports on the biological characterization of these cell populations by the use of xenograft models.

Approaches to dendritic cell-based immunotherapy after peripheral blood stem cell transplantation

High-dose chemotherapy with peripheral blood progenitor cell transplantation (PBPCT) is a potentially curative treatment option for patients with both hematological malignancies and solid tumors, including breast cancer. However, based on a number of clinical studies, there is strong evidence that minimal residual disease (MRD) persists after high-dose chemotherapy in a number of patients, which eventually results in disease recurrence. Therefore, several approaches to the treatment of MRD are currently being evaluated, including treatment with dendritic cell (DC)-based cancer vaccines. DCs, which play a crucial role with regard to the initiation of T-lymphocyte responses, can be generated ex vivo either from CD34+ hematopoietic progenitor cells or from blood monocytes. They can be pulsed in vitro with tumor-derived peptides or proteins, and then used as a professional antigen-presenting cell (APC) vaccine for the induction of antigen-specific T-lymphocytes in vivo. This paper summarizes our preclinical studies on the induction of primary HER-2/neu specific cytotoxic T-lymphocyte (CTL) responses using peptide-pulsed DC. As HER-2/neu is overexpressed on 30-40% of breast and ovarian cancer cells, this novel vaccination approach might be particularly applicable to advanced breast or ovarian cancer patients after high-dose chemotherapy and autologous PBPCT.

Expression of novel surface antigens on early hematopoietic cells

The purpose of this report is to demonstrate the expression of very recently identified surface antigens on CD34+ and AC133+ bone marrow (BM) cells. Coexpression analysis of AC133 and defined antigens on CD34+ BM cells revealed that the majority of the CD164+, CD135+, CD117+, CD38low, CD33+, and CD71low cells resides in the AC133+ population. In contrast, most of the CD10+ and CD19+ B cell progenitors and a fraction of the CD71high population are AC133-, indicating that CD34+AC133+ cells are enriched in primitive and myeloid progenitor cells, whereas CD34+AC133- cells mainly consist of B cell and late erythroid progenitors. This corresponds to the highly reduced percentage of CD10+ B cells and the absence of CD71high erythroid progenitors on AC133+ selected BM cells. A portion of 0.2-0.7% of the AC133+ selected cells do not coexpress CD34. These cells are very small and define a uniform CD71-, CD117-, CD10-, CD38low, CD135+, HLA-DRhigh, CD45+ population with unknown delineation. Four color analysis on CD34+CD38- BM cells revealed that virtually all of these primitive cells express AC133. Using an improved liposome-enhanced labeling technique for the staining of weakly expressed antigens, subsets of this population could be identified which express the angiopoietin receptors TIE (67.6%) and TEK (36.8%), the vascular endothelial growth factor receptors FLT1 (7%), FLT4 (3.2%), and KDR (10.4%), or the receptor tyrosine kinases HER-2 (15.4%) and FLT3 (CD135; 77.6%). Our results suggest that the CD34+CD38- population is heterogeneous with respect to the expression of the analyzed receptor tyrosine kinases.

Isolation of highly purified autologous and allogeneic peripheral CD34+ cells using the CliniMACS device

The CliniMACS CD34+ selection device was used for positive selection of apheresis products for autologous transplantation from 10 patients with malignant diseases and for allogeneic transplantation from 26 healthy donors. A total of 71 separations were performed. In 1 allogeneic donor, CD34+ progenitors were also isolated from bone marrow. Between 0.27 and 8.9 x 10(10) nucleated cells (median 4.9 x 10(10)) containing 0.09%-10.8% (median 0.67%) CD34+ progenitor cells were separated. After separation, a median number of 227 x 10(6) mononuclear cells (MNC) (51-524) were recovered, with a median viability of 99% (22%-100%) and a median purity of 97.0% (68.3%-99.7%) CD34+ cells. Depletion of T cells was extensive, with a median of 0.04% residual CD3+ cells (range <0.01%-0.92%). Residual CD19+ cells were between <0.01% and 17%, including CD34+CD19+ cells. Recovery of CD34+ cells was calculated according to the ISHAGE guidelines and ranged from 24% to 105% (median 71%). We conclude that with the CliniMACS device CD34+ cells with high purity and recovery can be isolated with concomitant effective T cell depletion in the allogeneic setting and with a high purging efficacy in the autologous setting.

The sialomucin CD164 (MGC-24v) is an adhesive glycoprotein expressed by human hematopoietic progenitors and bone marrow stromal cells that serves as a potent negative regulator of hematopoiesis

Mucin-like molecules represent an emerging family of cell surface glycoproteins expressed by cells of the hematopoietic system. We report the isolation of a cDNA clone that encodes a novel transmembrane isoform of the mucin-like glycoprotein MGC-24, expressed by both hematopoietic progenitor cells and elements of the bone marrow (BM) stroma. This molecule was clustered as CD164 at the recent workshop on human leukocyte differentiation antigens. CD164 was identified using a retroviral expression cloning strategy and two novel monoclonal antibody (MoAb) reagents, 103B2/9E10 and 105.A5. Both antibodies detected CD164/MGC-24v protein expression by BM stroma and subpopulations of the CD34(+) cells, which include the majority of clonogenic myeloid (colony-forming unit-granulocyte-macrophage [CFU-GM]) and erythroid (blast-forming unit-erythroid [BFU-E]) progenitors and the hierarchically more primitive precursors (pre-CFU). Biochemical and functional characterization of CD164 showed that this protein represents a homodimeric molecule of approximately 160 kD. Functional studies demonstrate a role for CD164 in the adhesion of hematopoietic progenitor cells to BM stromal cells in vitro. Moreover, antibody ligation of CD164 on primitive hematopoietic progenitor cells characterized by the cell surface phenotype CD34(BRIGHT)CD38(-) results in the decreased recruitment of these cells into cell cycle, suggesting that CD164 represents a potent signaling molecule with the capacity to suppress hematopoietic cell proliferation.

CD164, a novel sialomucin on CD34(+) and erythroid subsets, is located on human chromosome 6q21

CD164 is a novel 80- to 90-kD mucin-like molecule expressed by human CD34(+) hematopoietic progenitor cells. Our previous results suggest that this receptor may play a key role in hematopoiesis by facilitating the adhesion of CD34(+) cells to bone marrow stroma and by negatively regulating CD34(+) hematopoietic progenitor cell growth. These functional effects are mediated by at least two spatially distinct epitopes, defined by the monoclonal antibodies (MoAbs), 103B2/9E10 and 105A5. In this report, we show that these MoAbs, together with two other CD164 MoAbs, N6B6 and 67D2, show distinct patterns of reactivity when analyzed on hematopoietic cells from normal human bone marrow, umbilical cord blood, and peripheral blood. Flow cytometric analyses revealed that, on average, 63% to 82% of human bone marrow and 55% to 93% of cord blood CD34(+) cells are CD164(+), with expression of the 105A5 epitope being more variable than that of the other identified epitopes. Extensive multiparameter flow cytometric analyses were performed on cells expressing the 103B2/9E10 functional epitope. These analyses showed that the majority (>90%) of CD34(+) human bone marrow and cord blood cells that were CD38(lo/-) or that coexpressed AC133, CD90(Thy-1), CD117(c-kit), or CD135(FLT-3) were CD164(103B2/9E10)+. This CD164 epitope was generally detected on a significant proportion of CD34(+)CD71(lo/-) or CD34(+)CD33(lo/-) cells. In accord with our previous in vitro progenitor assay data, these phenotypes suggest that the CD164(103B2/9E10) epitope is expressed by a very primitive hematopoietic progenitor cell subset. It is of particular interest to note that the CD34(+)CD164(103B2/9E10)lo/- cells in bone marrow are mainly CD19(+) B-cell precursors, with the CD164(103B2/9E10) epitope subsequently appearing on CD34(lo/-)CD19(+) and CD34(lo/-)CD20(+) B cells in bone marrow, but being virtually absent from B cells in the peripheral blood. Further analyses of the CD34(lo/-)CD164(103B2/9E10)+ subsets indicated that one of the most prominent populations consists of maturing erythroid cells. The expression of the CD164(103B2/9E10) epitope precedes the appearance of the glycophorin C, glycophorin A, and band III erythroid lineage markers but is lost on terminal differentiation of the erythroid cells. Expression of this CD164(103B2/9E10) epitope is also found on developing myelomonocytic cells in bone marrow, being downregulated on mature neutrophils but maintained on monocytes in the peripheral blood. We have extended these studies further by identifying Pl artificial chromosome (PAC) clones containing the CD164 gene and have used these to localize the CD164 gene specifically to human chromosome 6q21.

Endoglin, a component of the TGF-beta receptor system, is a differentiation marker of human choriocarcinoma cells

Endoglin is an integral membrane glycoprotein that binds transforming growth factor-beta1 (TGF-beta1) with high affinity and it is strongly expressed on syncytiotrophoblasts throughout pregnancy. Here, we describe the expression of endoglin by the choriocarcinoma cell line JAR as evidenced by flow cytometry, immunoprecipitation, Western blot and reverse transcriptase polymerase chain reaction analyses. Cross-linking experiments of [125I]-labeled TGF-beta1 to JAR cells indicated that endoglin expressed at the surface of these cells binds TGF-beta. Furthermore, staining of human choriocarcinoma tissue sections with a polyclonal antibody to endoglin demonstrated a high expression of endoglin in syncytiotrophoblast-like areas, as opposed to a negative staining of cytotrophoblast-like cells. This pattern of endoglin expression was confirmed by experiments with methotrexate, an inducer of giant, multinucleated, non-proliferative cells, morphologically indistinguishable from the naturally occurring syncytiotrophoblasts. Thus, treatment of the JAR and JEG-3 choriocarcinoma cell lines with methotrexate led to an increase in endoglin expression, as demonstrated by Western and Northern blot analyses. Taken together, our results suggest that endoglin, in addition to being involved in placental development, may also be a cellular differentiation marker.

A case of bone marrow mastocytosis associated with multiple myeloma

Mastocytosis is a term used for a spectrum of disorders characterized by abnormal growth and accumulation of mast cells. The cutaneous variants of the disease have to be distinguished from systemic mastocytosis (SM), in which at least one extracutaneous organ is involved. In contrast to cutaneous mastocytosis, SM is often associated with another hematologic neoplasm. In most cases clonal myeloid malignancies such as a myeloproliferative or myelodysplastic syndrome occur. In a few cases of SM, however, clonal lymphoid disorders have been described. We here report on a case of SM associated with multiple myeloma. At first presentation, the 48-year old female patient showed monoclonal IgGlambda gammopathy and bone marrow (BM) mastocytosis, but no BM plasma cell infiltrates. Eight years later, the patient presented with BM mastocytosis and overt multiple myeloma. The co-existence of myeloma and mastocytosis was demonstrable by staining serial BM sections with antibodies against mast cell tryptase, CD68R, and the plasma cell marker VS38c. Interphase FISH analysis of BM sections revealed a numeric gain of chromosome 5 and chromosome 7 in the plasma cells but not in the mast cell infiltrates, thereby confirming the presence of two different neoplastic cell populations. To our knowledge, this is the first report describing the co-existence of multiple myeloma and mastocytosis.

Analysis of c-kit receptor dimerization by fluorescence resonance energy transfer

Stem cell factor (SCF) binding to the c-kit receptor triggers homodimerization and intermolecular tyrosine phosphorylation of the c-kit receptor, thus initiating signal transduction. Receptor dimerization is a critical early step in this process. Prior biochemical studies of c-kit receptor dimerization have mainly used affinity cross-linking techniques, which are beset with problems including low efficiency of cross-linking and the usual requirement for radiolabeled SCF to detect the cross-linked complex. We used the fluorescence resonance energy transfer (FRET) technique to examine the effects of SCF and other hematopoietic cytokines on c-kit receptor dimerization. The nonneutralizing anti-c-kit receptor monoclonal antibody 104D2 was directly conjugated to fluorescein isothiocyanate (FITC) or to the carbocyanine dye Cy3 and used to label cytokine-responsive human hematopoietic cell lines. The ability of SCF to induce c-kit receptor dimerization was assessed by flow cytometric analysis of FRET between the donor fluorochrome FITC and the acceptor fluorochrome Cy3. SCF induced a dose-dependent increase in c-kit receptor dimerization that correlated well with the concentrations of SCF required to stimulate cell proliferation. Receptor dimerization was detectable within 3 minutes after the addition of SCF and was maximal 30 minutes after the addition of SCF. Confocal microscopy showed redistribution of the c-kit receptor (from a diffuse distribution on the cell surface to "caps" at one end of the cell) within 3 minutes after SCF addition, followed by receptor internalization. Reappearance of the c-kit receptor on the cell surface required new protein synthesis, suggesting that the c-kit receptor is not recycled to the cell surface after internalization. Finally, erythropoietin (Epo), but not the structurally and functionally related cytokine thrombopoietin (Tpo), stimulated c-kit receptor dimerization detectable by FRET, and tyrosine phosphorylation of the c-kit receptor. These results suggest that exposure to Epo can activate the c-kit receptor and provide further evidence for cross-talk between the Epo and c-kit receptors in human hematopoietic cell lines. Studies with progeny of burst-forming unit-erythroid (BFU-E) suggest that the FRET technique is sufficiently sensitive to detect c-kit receptor dimerization on normal human hematopoietic cells.

Functional and phenotypic characterization of cord blood and bone marrow subsets expressing FLT3 (CD135) receptor tyrosine kinase

The class III receptor tyrosine kinase FLT3/FLK2 (FLT3; CD135) represents an important molecule involved in early steps of hematopoiesis. Here we compare cell-surface expression of FLT3 on bone marrow (BM) and cord blood (CB) cells using monoclonal antibodies (MoAbs) specific for the extracellular domain of human FLT3. Flow cytometric analysis of MACS-purified BM and CB cells showed that 63% to 82% of BM CD34+ and 88% to 95% of the CB CD34+ cells coexpress FLT3. Clonogenic assays and morphological characterization of FACS-sorted BM CD34+ cells demonstrate that colony-forming unit-granulocyte-macrophage (CFU-GM) and immature myelo-monocytic precursor cells are enriched in the subpopulation staining most brightly with the FLT3 MoAb whereas the majority of the burst-forming units-erythroid (BTU-E) and small cells with lymphoid morphology are found in the FLT3- population. In contrast, statistically indistinguishable proportions of CFU-granulocyte-erythrocyte-megakaryocyte-macrophage (CFU-GEMM) and more primitive cobblestone area forming cells (CAFC) were detected in both fractions, albeit the FLT3+ fraction consistently showed more CAFC activity than the FLT3- fraction. Although in both, BM and CB the majority of CD34+CD117+ (KIT+), CD34+CD90+ (Thy-1+), and CD34+CD109+ cells coexpress FLT3, three-color phenotypic analyses are consistent with the functional findings and suggest that the most primitive cells defined as CD34+CD38-, CD34+CD71low, CD34+HLA-DR-, CD34+CD117low, CD34+CD90+, and CD34+CD109+ express low levels of cell-surface FLT3 and were therefore not enriched to a statistically significant extent with the bright versus negative sorting scheme. Thus, clear segregation of the most primitive progenitors from BM CD34+ cells was confounded by low apparent levels of FLT3 cell-surface expression on these cells, whereas myeloid progenitors unambiguously segregated with the FLT3 brightest cells and erythroid progenitors with the FLT3 dimmest. Additional phenotypic analyses using MoAbs against progenitor/stem cell markers including the mucinlike molecule MGC-24v (CD164), the receptor tyrosine kinases TIE, FMS (CD115), and KIT (CD117) further illustrate the differences in surface antigen expression profiles of BM and CB CD34+ cells. Notably, CD115 is rarely detected on CB CD34+ cells, whereas 20% to 25% of the BM CD34+FLT3+ cells are CD115+. Furthermore, 80% to 95% of the CB CD34+CD117+ but only 60% to 75% of the BM CD34+CD117+ cells coexpress FLT3. Only a negligible amount of CD34+CD19+ are detected in CB, while in BM 20% to 30% of CD34+CD19+ presumed pro/pre-B cells coexpress FLT3. In contrast, the majority of the CD34+CD164+ and CD34+TIE+ subsets in both CB and BM coexpress FLT3. Analysis of unseparated cells showed that FLT3 expression is not restricted to CD34+ subsets. About 65% to 70% of lymphocyte-gated BM CD34-FLT3+ cells are positive for the monocytic marker CD115 whereas 25% to 30% of these cells consist of CD10 expressing B-cell precursors. Finally, CD34- monocytes in BM, CB, and PB express FLT3 whereas granulocytes are FLT3-. Our data show that detectable FLT3 appears first at low levels on the surface of primitive multilineage progenitor cells and disappears during defined stages of B-cell development, but is upregulated and maintained during monocytic maturation.

Analysis of Tie receptor tyrosine kinase in haemopoietic progenitor and leukaemia cells

We generated a panel of monoclonal antibodies against the extracellular domain of the Tie receptor tyrosine kinase and studied its expression in human haemopoietic and tumour cell lines and in samples from leukaemia patients. Most of the erythroblastic/megakaryoblastic (6/8), 2/7 myeloid and 3/6 B-lymphoblastic leukaemia cell lines were Tie-positive. The erythroblastic/megakaryoblastic leukaemia cell lines also expressed the related Tie-2/Tek gene and, surprisingly, its recently cloned ligand gene angiopoietin-1, which was located in chromosome 8q23.1. In addition, 16% of freshly isolated leukaemia samples were Tie positive. Peripheral blood mononuclear cells were Tie negative, but a few Tie positive cells were found in immunoperoxidase staining of mobilized peripheral blood stem cells. Long-term culture of isolated umbilical cord blood CD34+ Tie+ and CD34+ Tie- cells indicated that the Tie+ fraction contained a slightly higher frequency of cobblestone area forming cells (CAFC). Thus, Tie is expressed on haemopoietic progenitor cells and some leukaemic blasts. The coexpression of Tie-2 and angiopoietin-1 in megakaryoblastic leukaemia cell lines suggests the existence of an autocrine ligand/receptor signalling loop in these cells.

Flk-1 expression defines a population of early embryonic hematopoietic precursors

We have investigated the expression pattern of the Flk-1 receptor tyrosine kinase in mouse embryonic and fetal hematopoietic tissues as well as on hematopoietic precursor cells derived from these tissues. RNA analysis indicated that flk-1 was expressed in the yolk sac at day 10 of gestation, in the whole embryo at day 10 and 12 of gestation, in the liver throughout fetal life and in embryoid bodies (EBs) generated from ES cells differentiated in culture. Flk-1 message was also detected in erythroid and macrophage colonies generated from precursors of yolk sac, fetal liver, adult marrow and EB origin. Using an antibody directed against the extracellular portion of the molecule we have found that up to 50% of cells from EBs differentiated for 4 days express Flk-1. Following the development of this early Flk-1+ population the number of receptor-positive cells declines progressively to represent less than 5% of the EBs by day 12 of differentiation. Kinetic analysis revealed that the establishment of the EB Flk-1+ population precedes the development of cells which express CD34, Ly6A (Sca-1) and AA4.1. Cell sorting experiments demonstrated that all day-4 EB-derived hematopoietic precursors are Flk-1+ whereas greater than 95% of those found within the day-12 EBs are Flk-1-, suggesting that the precursor population which expresses this receptor represents an early but transient wave of hematopoietic development. Analysis of yolk sac and whole embryos at day 8.5 of gestation revealed a small but distinct Flk-1+ population that contained hematopoietic precursors. Day-12.5 fetal liver contained few Flk-1+ cells that showed little hematopoietic potential. Together these findings indicate that Flk-1 is expressed on an early population of hematopoietic precursors that may represent the onset of embryonic hematopoiesis.

Parameters predicting response to alpha-interferon treatment in chronic hepatitis C

BACKGROUND/AIMS

Sustained response to alpha-interferon treatment for chronic hepatitis C is seen in only 25% of cases. Therefore, it is desirable to define pretreatment factors predicting responders.

MATERIALS AND METHODS

Forty-nine patients with chronic hepatitis C were treated with a standard alpha-interferon regimen (3 x 3 MU s.c./week). Demographic, biochemical and immunological parameters, and HCV genotypes were obtained prior to initiation of treatment and evaluated for their value in predicting response to alpha-interferon therapy.

RESULTS

Response, as defined by normalization of ALT, was 71% during interferon therapy and sustained response after discontinuation of interferon 24.5%. Patients infected with HCV-genotype 1b had significantly more often "community-acquired" disease. Their outcome was worse with a response rate of 44% during therapy and a sustained response of 12.5%, as compared to 87% and 27% respectively in patients infected with genotypes other than 1b. On multivariate analysis, absence of cirrhosis, HCV-genotype other than 1b, higher ALT levels and higher numbers of CD8 positive liver infiltrates were found to be predictors of response during alpha-interferon therapy.

CONCLUSION

Response to alpha-interferon therapy seems to be influenced both by viral virulence factors and by the intensity of the host immune response to HCV.

Preclinical studies with Fc(gamma)R bispecific antibodies and granulocyte colony-stimulating factor-primed neutrophils as effector cells against HER-2/neu overexpressing breast cancer

Immunotherapies directed to the proto-oncogene product HER-2/neu, which is overexpressed on a subset of breast and other carcinomas, currently receive considerable attention. We have investigated cell-mediated effector mechanisms of HER-2/neu antibodies against breast cancer cell lines. Compared to unfractionated control blood, whole blood from patients during granulocyte colony-stimulating factor (G-CSF) treatment exhibits significantly enhanced lysis (P < 0.001) of SK-BR-3 cells in the presence of HER-2/neu antibody 520C9. The extent of tumor cell killing correlated positively (r = 0.74) to polymorphonuclear neutrophil (PMN) blood counts. Fractionation of whole blood into plasma, mononuclear cells, and PMNs showed major killing capacity to reside in the granulocyte fraction. PMNs were efficiently cytolytic with a panel of HER-2/neu antibodies and against various breast cancer cell lines. Experiments with blocking antibodies to Fc(gamma)R documented Fc(gamma)RII (CD32) as the major trigger molecule for monoclonal antibody 502C9-mediated cytotoxicity. Killing via 520C9 was significantly influenced by an allotypic polymorphism of Fc(gamma)RIIa, the CD32 molecule expressed on PMNs. In reverse antibody-dependent cell-mediated cytotoxicity experiments with a panel of HER-2/neu-directed bispecific antibodies, Fc(gamma)RIII (CD16) proved to be an efficient trigger molecule in blood from healthy volunteers. During G-CSF treatment, however, Fc(gamma)RI (CD64)-expressed on monocytes and G-CSF primed, but not on healthy donor PMNs-became the predominant cytotoxic trigger molecule. Thus, G-CSF application increased effector cell numbers for HER-2/neu-directed immunotherapy, and G-CSF primed PMNs proved particularly effective with a [HER-2/neu x Fc(gamma)RI] bispecific antibody. These findings support clinical trials with HER-2/neu-directed antibodies in combination with G-CSF in breast cancer patients overexpressing HER-2/neu.

Surface antigen expression on CD34+ cord blood cells: comparative analysis by flow cytometry and limiting dilution (LD) RT-PCR of chymopapain-treated or untreated cells

Expression of antigens coexpressed on cord blood (CB) CD34+ cells was evaluated by flow cytometry analysis and reverse transcriptase polymerase chain reaction (RT-PCR). Antigen expression was also comparatively analyzed by flow cytometry and limiting dilution (LD) RT-PCR to investigate effects of chymopapain on epitopes of several cell surface markers: LD RT-PCR allows detection of the expression of antigens degraded by chymopapain which are not identified by flow cytometry. Monoclonal antibodies (MoAbs) that recognize chymopapain resistant epitopes on several coexpressed cell surface markers were identified: these included MoAbs directed against CD11a, CD13, CD18, CD38, CD45RO, CD51, HLA-DR, Thy-1, c-kit, flt-3 (STK-1), and mdr-1. Interestingly, chymopapain treatment caused enhanced staining with MoAbs against HLA-DR, Thy-1, flt-3, mdr-1, and CD51. The frequency (LD RT-PCR) of CD18, CD38, Thy-1, and c-kit RT-PCR signals on pure sorted CD34+ CD18-, CD34+ CD38-, CD34+ Thy-1-, and CD34+ c-kit- cells, respectively, was similar in corresponding subsets treated or not with chymopapain. In contrast, the frequency of CD33 RT-PCR signals on sorted CD34+ CD33- cells was higher in chymopapain-treated samples than in untreated samples and thus confirmed at the transcriptional level that the epitope recognized by anti-CD33 is chymopapain sensitive. Our findings extend data on the phenotypic profile of CB CD34+ cells and show that several key cell surface markers of hematopoietic progenitor cells are chymopapain resistant. In addition, the results of the present study demonstrate that the RT-PCR can be applied to the analysis of multiple RNA species in small numbers of hematopoietic progenitor cells and show that LD RT-PCR allows the identification and frequency determination of rare cells which are undetectable by flow cytometry.

The Tie receptor tyrosine kinase is expressed by human hematopoietic progenitor cells and by a subset of megakaryocytic cells

Growth factor receptors in human hematopoietic progenitor cells have become the focus of intense interest, because they may provide tools for the monitoring, enrichment, and expansion of stem cells. We have shown earlier that the Tie receptor tyrosine kinase is expressed in erythroid and megakaryoblastic human leukemia cell lines, in the blood islands of the yolk sac, and in endothelial cells starting from day 8.0 of mouse development. Here, the expression of Tie was studied in human hematopoietic cells of various sources. Peripheral blood mononuclear cells were Tie-. However, a large fraction of CD34+ cells from umbilical cord blood (UCB) and bone marrow (BM) expressed tie protein and mRNA. On average, 64% of the fluorescence-activated cell sorting-gated UCB CD34+ cells including CD38- cells and a fraction of cells expressing low levels of c-Kit were Tie+. Also, 30% to 60% of BM CD34+ cells were Tie+, including most of the BM CD34+CD38-, CD34+Thy-1+, and CD34+HLA-DR- cells. Under culture conditions allowing myeloid, erythroid, and/or megakaryocytic differentiation, purified UCB CD34+ cells lost Tie mRNA and protein expression concomitantly with that of CD34; however, a significant fraction of cells expressed Tie during megakaryocytic differentiation. These data suggest that, in humans, the Tie receptor and presumably its ligand may function at an early stage of hematopoietic cell differentiation.

Human FLT3/FLK2 receptor tyrosine kinase is expressed at the surface of normal and malignant hematopoietic cells

FLT3/FLK2 is a receptor tyrosine kinase (RTK) which is thought to play an important role in early stages of hematopoiesis. Monoclonal antibodies (mAbs) against the extracellular domain of human FLT3 were generated to study the cell surface expression of this class III RTK on normal bone marrow cells and on leukemic blasts from patients with acute leukemias. Functional analysis of five mAbs (SF1 series) revealed that all of them can mimic to variable extents the activity of the FLT3 ligand (FL) upon receptor activation and modulation, while only one mAb weakly inhibited ligand binding. Using flow cytometry, we detected surface expression of FLT3 on cell lines of the myeloid (4/8) and B lymphoid (7/10) lineages. On normal human bone marrow cells, the expression of FLT3 is restricted, in agreement with a presumed function of this receptor at the level of the stem cells and early committed progenitors. Expression of FLT3 was found on a fraction of CD34-positive and CD34-negative cells. Three-color analysis further revealed that most of the CD34 FLT3+ cells coexpress CD117 (KIT) at a high level. Finally, FLT3 is expressed on leukemic blasts of 18/22 acute myeloid leukemias (AML) and 3/5 acute lymphoid leukemias (ALL) of the B lineage, providing a possible application in diagnosis and therapy of these diseases.

Expression and signal transduction of the FLT3 tyrosine kinase receptor

FLT3 is a receptor tyrosine kinase of 130-55 kDa expressed on normal bone marrow stem and early progenitor cells and on leukemic blasts from patients with acute leukemias. The FLT3 ligand, FL, is a new cytokine which acts on hematopoietic progenitors in synergy with other cytokines. FLT3 transduces FL-mediated signal through interaction with a number of cytoplasmic substrates.

The adhesion molecule E-cadherin and a surface antigen recognized by the antibody 9C4 are selectively expressed on erythroid cells of defined maturational stages

The antigen expression of immature erythroid bone marrow cells was studied using two recently generated monoclonal antibodies (mAb), mAb 67A4 and 9C4, with specificities for the epithelial cell adhesion molecule E-cadherin (E-cad; mAb 67A4), and a novel 110 kDa differentiation antigen (mAb 9C4) with unknown molecular structure. Pappenheim staining of FACS-purified cells labeled with mAb 9C4 and anti-glycophorin A (GA) revealed that the majority of the 9C4+GA- and 9C4+GA+ cells consisted of erythroblasts. In contrast, the E-cad-positive population comprised normoblasts and erythroblasts. While the E-cad+GA- fraction contained mainly erythroblasts and basophilic normoblasts, the E-Cad+GA+ population was enriched in orthochromatic and polychromatophilic normoblasts. By colony assays of affinity column-purified cells it could be shown that erythroid colony forming units (CFU-E) were enriched and erythroid burst forming units (BFU-E) were depleted in the 9C4- and E-cad-positive fractions. Flow cytometric analysis of bone marrow cells double-labeled with mAb 67A4 and anti-CD71, anti-CD117, anti-CD34, or anti-GA revealed that about 90% of the E-cad-positive cells coexpressed CD71, about 70% were positive for CD117, about 50% for GA, and only about 5% coexpressed CD34. The expression pattern of 9C4 antigen was similar to that of E-Cad with the exception that only a minority of the 9C4-positive cells coexpressed GA. Lymphoid and myeloid markers were negative on both the E-Cad- and 9C4-positive populations. In these studies we describe the identification of a new mAb-defined antigen which is specifically expressed on erythroblasts and CFU-E(9C4) and demonstrate that E-Cad is not only expressed on epithelial cells but also on erythropoietic cells of defined maturational stages.

Effects of hematopoietic growth factors on interleukin 6 secretion by blast cells derived from acute myelogenous leukemia patients

Interleukin 6 (IL6) secretion by blast cells derived from peripheral blood of patients with acute myelogenous leukemia (AML) was characterized. IL6 secretion showed a wide variation both when AML blasts were cultured in medium alone and in the presence of exogenous cytokines. The level of IL6 secretion was significantly correlated to secretion of other cytokines (IL1 alpha, IL1 beta, granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, tumor necrosis factor alpha). IL1 beta, granulocyte-macrophage colony-stimulating factor, macrophage colony-stimulating factor and stem cell factor increased IL6 secretion, whereas IL4 caused decreased IL6 secretion together with increased release of IL1 receptor antagonist.

Effects of interleukin 10 on blast cells derived from patients with acute myelogenous leukemia

The effect of interleukin 10 (IL-10) on proliferation and cytokine secretion by acute myelogenous leukemia (AML) blast cells was investigated in vitro. IL-10 inhibited spontaneous AML blast proliferation for a majority of patients, whereas in the presence of exogenous growth factors (granulocyte-stimulating factor, G-CSF; granulocyte-macrophage colony-stimulating factor, GM-CSF; interleukin 3) the IL-10 effect on blast proliferation showed a wide variation depending on the individual AML patient. IL-10 seemed to cause an irreversible inhibitory effect on AML blasts, as inhibition could also be demonstrated when IL-10 was present only during the initial preincubation of the leukemia cells. IL-10 also inhibited AML blast colony formation. However, independent of the effect on AML blast proliferation, IL-10 decrease cytokine secretion from AML blast cells for all patients, as demonstrated for IL-1 alpha, IL-1 beta, tumor necrosis factor-alpha, GM-CSF and interleukin 6. IL-10 did not inhibit development of apoptosis in AML blasts cultured in vitro. Expression of complement receptors and capability to adhere and internalize bacteria by AML blasts were not altered by IL-10.

E-cadherin is functionally involved in the maturation of the erythroid lineage

Differentiation and proliferation of hematopoietic progenitors take place in the bone marrow and is a tightly controlled process. Cell adhesion molecules of the integrin and immunoglobulin families have been shown to be involved in these processes, but almost nothing was known about the involvement of the cadherin family in the hematopoietic system. A PCR screening of RNA of human bone marrow mononuclear cells with specific primers for classical cadherins revealed that E-cadherin, which is mainly expressed by cells of epithelial origin, is also expressed by bone marrow cells. Western blot analysis and immunofluorescence staining of bone marrow sections confirmed this unexpected finding. A more detailed analysis using immunoaffinity columns and dual color flow cytometry showed that the expression of E-cadherin is restricted to defined maturation stages of the erythropoietic lineage. Erythroblasts and normoblasts express E-cadherin, mature erythrocytes do not. A functional role of E-cadherin in the differentiation process of the erythroid lineage was indicated by antibody-inhibition studies. The addition of anti-E-cadherin antibody to bone marrow mononuclear cultures containing exogeneous erythropoietin drastically diminished the formation of erythropoietic cells. These data suggest a non-anticipated expression and function of E-cadherin in one defined hematopoietic cell lineage.