CD3(+) and/or CD14(+) depletion from cord blood mononuclear cells before ex vivo expansion culture improves total nucleated cell and CD34(+) cell yields

Cord blood (CB) is used increasingly in transplant patients lacking sibling or unrelated donors. A major hurdle in the use of CB is its low cell dose, which is largely responsible for an elevated risk of graft failure and a significantly delayed neutrophil and platelet engraftment. As a positive correlation has been shown between the total nucleated cell (TNC) and CD34(+) cell dose transplanted and time to neutrophil and platelet engraftment, strategies to increase these measures are under development. One strategy includes the ex vivo expansion of CB mononuclear cells (MNC) with MSC in a cytokine cocktail. We show that this strategy can be further improved if CD3(+) and/or CD14(+) cells are first depleted from the CB MNC before ex vivo expansion. Ready translation of this depletion strategy to improve ex vivo CB expansion in the clinic is feasible as clinical-grade devices and reagents are available. Ultimately, the aim of improving TNC and CD34(+) transplant doses is to further improve the rate of neutrophil and platelet engraftment in CB recipients.

Proinflammatory cytokines inhibit osteogenic differentiation from stem cells: implications for bone repair during inflammation

OBJECTIVE

The effects of inflammation on bone development from mesenchymal stem cells (MSC) are unclear due to the difficulty in isolating MSC. The aim of this study was to develop a MSC isolation method and to determine the in vitro effects of interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha) on their osteogenic differentiation.

METHODS

Murine MSC were isolated from the limbs of C57/Bl6 mice through collagenase digestion of bone and enriched as the Stem cell antigen (Sca-1)(+) CD31(-) CD45(-) population, using lineage immunodepletion, followed by fluorescence-activated cell sorting (FACS). They were differentiated along the osteoblast linage in the presence or absence of IL-1beta and TNFalpha. Mineralization was measured as was the expression of a number of osteogenic genes by quantitative polymerase chain reaction (PCR).

RESULTS

We show that osteogenic differentiation from the MSC population is suppressed by IL-1beta and TNFalpha. In addition to suppression of bone mineralization, both cytokines inhibited the differentiation-associated increases in alkaline phosphatase (ALP) activity and the gene expression for ALP, alpha1(I) procollagen, runt-related transcription factor 2 (Runx2) and osterix. However, only TNFalpha inhibited osteonectin and osteopontin mRNA expression and only IL-1beta reduced cell proliferation.

CONCLUSIONS

The convenient isolation technique enables the easy generation of sufficient MSC to permit the molecular analysis of their differentiation. We were thus able to show that the proinflammatory cytokines, IL-1beta and TNFalpha, can compromise bone development from this primary MSC population, although with some significant differences. The potential involvement of specific inflammatory mediators needs to be taken into account if optimal bone repair and presumably that of other tissues are to be achieved with MSC.

Epitope recognition of antibodies that define the sialomucin, endolyn (CD164), a negative regulator of haematopoiesis

Endolyn (CD164) is a sialomucin that functions as an adhesion molecule and a negative regulator of CD34+ CD38- human haematopoietic precursor cell proliferation. The 105A5 and 103B2/9E10 CD164 monoclonal antibodies (mAbs), which act as surrogate ligands, recognize distinct glycosylation-dependent classes I and II epitopes located on domain I of the native and recombinant CD164 proteins. Here, we document five new CD164 mAbs, the 96 series, that rely on conformational integrity, but not glycosylation, of exons 2- and 3-encoded CD164 domains, thereby resembling the class III mAbs, N6B6 and 67D2. Although all the 96 series class III mAbs labelled both the 105A5+ and 103B2/9E10+ cells, cross-competition and immunoblotting studies allow them to be categorized into two distinct class III subgroups, i.e. the N6B6-like subgroup that only recognizes 80-100 kDa proteins and the 67D2-like subgroup that also recognizes a higher molecular weight (>220 kDa) form. To more closely define the reactivity patterns of mAbs to the classes I and II epitopes, the global glycosylation patterns of the soluble human (h) CD164 proteins were determined using lectin binding, high-performance liquid chromatography (HPLC) and mass spectrometry. hCD164 recombinant proteins bound to the lectins, Galanthus nivalis agglutinin, Datura stramonium agglutinin, Sambucus nigra agglutinin, Maackia amurensis agglutinin and peanut agglutinin, indicating the presence of high mannose and complex N-glycans, in addition to core 1 O-glycans (the Tn antigen) and alpha2-3 and alpha2-6 sialic acid moieties. Our HPLC and mass spectrometry results revealed both high mannose and complex N-glycosylation with various numbers of branches increasing the complexity of the glycosylation pattern. Most O-glycans were small, core 1 or 2 based. High levels of sialylation in alpha2-3 and alpha2-6 linkages, without sialyl-Lewis X, indicate that the majority of these hCD164 recombinant proteins are unable to bind to selectins in our assay system, but may interact with Siglec molecules.

A novel epitope of CD59 expressed by primitive human hematopoietic progenitors

OBJECTIVE

The aim of this study was to determine the identity of the cell surface molecule on primitive hematopoietic cells recognized by monoclonal antibody HCC-1.

MATERIALS AND METHODS

Screening of a cDNA expression library prepared from human bone marrow stromal cells with HCC-1 yielded a single cDNA, which when expressed in FDCP-1 cells, resulted in the specific acquisition of HCC-1 binding. The cDNA demonstrated complete identity with CD59, a phosphoinositol glycan-linked membrane protein that protects cells against autologous complement attack. The ubiquitous expression of CD59 is in marked contrast to the restricted reactivity of HCC-1. Studies were performed to examine the basis for the novel specificity of HCC-1 for CD59. The epitope on CD59 identified by HCC-1 was mapped using a series of rat/human CD59 chimeric proteins. Immunoprecipitation analyses were performed to determine whether CD59 associates with other membrane proteins.

RESULTS

Mutagenesis of Asn18 did not alter the binding of HCC-1 to CD59, suggesting that N-linked carbohydrates are not responsible for the binding specificity of HCC-1. The epitope for HCC-1 was shown to differ from that identified by previously described CD59 antibodies, encompassing residues A31, L33, R55, and L59. An 80 kDa protein co-immunoprecipitated with CD59 in the HCC-1(-) cell line HL-60 but not in HCC-1(+) K562 cells.

CONCLUSION

Collectively, these data support the hypothesis that the unique specificity of HCC-1 for CD59 is due in part to recognition of a novel epitope, which is masked as a result of association with an as yet unidentified 80 kDa protein.

Vascular cell adhesion molecule-1 (CD106) is cleaved by neutrophil proteases in the bone marrow following hematopoietic progenitor cell mobilization by granulocyte colony-stimulating factor

Mobilized progenitor cells currently represent the most commonly used source of hematopoietic progenitor cells (HPCs) to effect hematopoietic reconstitution following myeloablative chemotherapies. Despite their widespread use, the molecular mechanisms responsible for the enforced egress of HPCs from the bone marrow (BM) into the circulation in response to mobilizing agents such as cytokines remain to be determined. Results of this study indicate that expression of vascular cell adhesion molecule-1 (VCAM-1) is strongly reduced in vivo in the BM during HPC mobilization by granulocyte colony-stimulating factor (G-CSF) and stem cell factor. Two serine proteases, namely, neutrophil elastase and cathepsin G, were identified, which cleave VCAM-1 and are released by neutrophils accumulating in the BM during the course of immobilization induced by G-CSF. The proposal is made that an essential step contributing to the mobilization of HPCs is the proteolytic cleavage of VCAM-1 expressed by BM stromal cells, an event triggered by the degranulation of neutrophils accumulating in the BM in response to the administration of G-CSF.

Monoclonal antibody BB9 raised against bone marrow stromal cells identifies a cell-surface glycoprotein expressed by primitive human hemopoietic progenitors

OBJECTIVE

The identification of cell-surface antigens whose expression is limited to primitive hematopoietic progenitor cells (HPC) is of major value in the identification, isolation, and characterization of candidate stem cells in human hemopoietic tissues. Based on the observation that bone marrow stromal cells and primitive HPC share several cell-surface antigens, we sought to generate monoclonal antibodies to HPC by immunization with cultured human stromal cells.

METHODS

BALB/c mouse were immunized with human bone marrow (BM)-derived stromal cells. Splenocytes isolated from immunized mice were fused with the NS-1 murine myeloma cell line and resulting hybridomas selected in HAT medium, then screened for reactivity against stromal cells, peripheral blood (PB), and BM cells.

RESULTS

A monoclonal antibody (MAb), BB9, was identified based on its binding to stromal cells, a minor subpopulation of mononuclear cells in adult human BM, and corresponding lack of reactivity with leukocytes in PB. BB9 bound to a minor subpopulation of BM CD34(+) cells characterized by high-level CD34 antigen and Thy-1 expression, low-absent expression of CD38, low retention of Rhodamine 123, and quiescent cycle status as evidenced by lack of labeling with Ki67. CD34(+)BB9(+) cells, in contrast to CD34(+)BB9(-) cells, demonstrated a capacity to sustain hematopoiesis in pre-CFU culture stimulated by the combination of IL-3, IL-6, G-CSF, and SCF. BB9 also demonstrated binding to CD34(+) cells from mobilized PB.

CONCLUSION

Collectively, these data therefore demonstrate that MAb BB9 identifies an antigen, which is selectively expressed by hierarchically primitive human HPC and also by stromal cells.

Mucin-like molecules as modulators of the survival and proliferation of primitive hematopoietic cells

Current data suggest that interplay between two classes of molecules contributes to the regulation of hematopoiesis: hematopoietic growth factors, which regulate the survival, proliferation, and development of primitive hematopoietic cells and cell adhesion molecules (CAMs), which are responsible for the localization of hematopoiesis to the bone marrow (BM) and for mediating physical association between developing hematopoietic cells and marrow stromal tissue. A range of cell surface molecules representing several CAM superfamilies including integrins, selectins, the immunoglobulin gene superfamily and an emerging family of mucin-like molecules (the sialomucins) are involved in supporting cell-cell and cell-extracellular matrix (ECM) interactions between primitive hematopoietic cells and the stromal cell-mediated hematopoietic microenvironment (HM) of the bone marrow. There is abundant evidence in non-hematopoietic tissues that CAMs are signalling molecules which participate in a range of signal transduction events important not only for regulating cell adhesion and motility, but also for cell growth and survival. Although the signalling functions of CAMs have not been studied extensively in primitive hematopoietic progenitors (HPCs), extrapolation from burgeoning data in other systems is consistent with the hypothesis that hematopoiesis within the BM is regulated by interaction between signals generated locally by CAMs and those elicited by cytokines. Evidence in support of this notion was initially provided by studies on normal HPCs demonstrating cross-talk between members of the integrin superfamily and cytokine receptors. In this article we review recent reports that mucin-like molecules are also signalling molecules on primitive hematopoietic cells and that the signals they deliver potently inhibit hematopoiesis.

Integrin-mediated interactions between human bone marrow stromal precursor cells and the extracellular matrix

To date, the precise interactions between bone marrow stromal cells and the extracellular matrix that govern stromal cell development remain unclear. The integrin super-family of cell-surface adhesion molecules represents a major pathway used by virtually all cell types to interact with different extracellular matrix components. In this study, purified populations of stromal precursor cells were isolated from the STRO-1-positive fraction of normal human marrow, by fluoresence-activated cell sorting, and then assayed for their ability to initiate clonogenic growth in the presence of various integrin ligands. Bone marrow-derived stromal progenitors displayed differential growth to fibronectin, vitronectin, and laminin, over collagen types I and III, but showed a similar affinity for collagen type IV. The integrin heterodimers alpha1beta1, alpha2beta1, alpha5beta1, alpha6beta1, alpha(v)beta3, and alpha(v)beta5 were found to coexpress with the STRO-1 antigen on the cell surface of CFU-F, using dual-color analysis. Furthermore, only a proportion of stromal precursors expressed the integrin alpha4beta1, while no measurable levels of the integrin alpha3beta1 could be detected. Subsequent adhesion studies using functional blocking antibodies to different integrin alpha/beta heterodimers showed that stromal cell growth on collagen, laminin, and fibronectin was mediated by multiple beta1 integrins. In contrast, cloning efficiency in the presence of vitronectin was mediated in part by alpha(v)beta3. When human marrow stromal cells were cultured under osteoinductive conditions, their ability to form a mineralized matrix in vitro was significantly diminished in the presence of a functional blocking monoclonal antibody to the beta1 integrin subunit. The results of this study indicate that beta1 integrins appear to be the predominant adhesion receptor subfamily utilized by stromal precursor cells to adhere and proliferate utilizing matrix glycoproteins commonly found in the bone marrow microenvironment and bone surfaces. Furthermore, these data suggest a possible role for the beta1 integrin subfamily during the development of stromal precursor cells into functional osteoblast-like cells.

Relationship between novel isoforms, functionally important domains, and subcellular distribution of CD164/endolyn

Functional analyses have indicated that the human CD164 sialomucin may play a key role in hematopoiesis by facilitating the adhesion of human CD34(+) cells to the stroma and by negatively regulating CD34(+)CD38(lo/-) cell proliferation. We have identified three novel human CD164 variants derived by alternative splicing of bona fide exons from a single genomic transcription unit. The predominant CD164(E1-6) isoform, encoded by six exons, is a type I transmembrane protein containing two extracellular mucin domains (I and II) interrupted by a cysteine-rich non-mucin domain. The 103B2/9E10 and 105A5 epitopes, which specify ligand binding characteristics, are located on the exon 1-encoded mucin domain I. Three human CD164(E1-6) mRNA species, exhibiting differential polyadenylation site usage, are differentially expressed in hematopoietic and non-hematopoietic tissues. This study provides additional evidence that human CD164(E1-6) represents the ortholog of murine MGC-24v and rat endolyn. Comparative analysis of murine MGC-24v/CD164(E1-6) with human CD164(E1-6) revealed two potential splice variants and a similar genomic structure. Whereas the human CD164 gene is located on chromosome 6q21, the mouse gene occurs in a syntenic region on chromosome 10B1-B2. By confocal microscopy, human CD164 in CD34(+)CD38(+) hematopoietic progenitor (KG1B) and epithelial cell lines appears to be localized primarily in endosomes and lysosomes, with low concentrations at the cell surface. However, in a minority of KG1B cells, CD164 is more prominently expressed at the plasma membrane and in the recycling endosomes, suggesting that its distribution is regulated in cells of hematopoietic origin.

Intrinsic noise at synapses between a wing hinge stretch receptor and flight motor neurons in the locust

Variability in postsynaptic potential (PSP) amplitude due to intrinsic noise limits the reliability of communication between neurons. I measured PSP variability at synapses between a forewing stretch receptor and wing depressor motor neurons in locusts, a pathway that is important in the control of flying. The intrinsic noise in the stretch receptor output synapse was measured by subtracting the background noise, originating in other synaptic pathways onto the motor neuron, from the variability in the amplitudes of PSPs evoked by the stretch receptor. Intrinsic synaptic noise caused successive PSPs to vary by 4–10 % in basalar and subalar flight motor neurons. Recordings from pairs of these wing depressor motor neurons showed that the amount of transmitter released varied independently between different output sites from the stretch receptor. Histograms of excitatory postsynaptic potential amplitude were normal distributions that lacked separate peaks. I estimate that quantal amplitude is significantly less than 0.1 mV and that several hundred quanta are released for each presynaptic spike. This accords well with a previous estimate of the number of discrete anatomical synapses and would facilitate modulation of output from the stretch receptor.

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.

Combination of stem cell factor and granulocyte colony-stimulating factor mobilizes the highest number of primitive haemopoietic progenitors as shown by pre-colony-forming unit (pre-CFU) assay

Fifty-two patients with poor prognosis carcinoma of the breast underwent peripheral blood stem cell (PBSC) mobilization using five different regimens. The yields of primitive haemopoietic progenitors were quantified by a recently described pre-colony-forming unit (pre-CFU) assay using limiting dilution analysis (LDA). Results of days 14 and 35 pre-CFU were also correlated with conventional CD34+ cell enumeration, CFU-GM (granulocyte-macrophage) and long-term culture-initiating cell (LTCIC) assays. The yield of pre-CFUs with the combination of granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF) was significantly higher than with G-CSF alone, cyclophosphamide (Cyclo) and granulocyte-monocyte colony-stimulating factor (GM-CSF), interleukin (IL)-3 and GM-CSF, or Cyclo alone. No significant correlation between neutrophil engraftment and pre-CFU could be demonstrated. Furthermore, CFU-GM was shown to bear a stronger correlation with pre-CFU and LTCIC than CD34+ cell measurement; thus, CFU-GM remains a useful biological tool for haemopoietic stem cell assay. We conclude that the combination of G-CSF and SCF mobilizes the highest number of pre-CFUs as measured by functional pre-CFU assay, which provides an alternative measurement of primitive haemopoietic progenitors to the LTCIC assay.

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.

The human AC133 hematopoietic stem cell antigen is also expressed in epithelial cells and targeted to plasma membrane protrusions

The human AC133 antigen and mouse prominin are structurally related plasma membrane proteins. However, their tissue distribution is distinct, with the AC133 antigen being found on hematopoietic stem and progenitor cells and prominin on various epithelial cells. To determine whether the human AC133 antigen and mouse prominin are orthologues or distinct members of a protein family, we examined the human epithelial cell line Caco-2 for the possible expression of the AC133 antigen. By both immunofluorescence and immunoprecipitation, the AC133 antigen was found to be expressed on the surface of Caco-2 cells. Interestingly, immunoreactivity for the AC133 antigen, but not its mRNA level, was down-regulated upon differentiation of Caco-2 cells. The AC133 antigen was specifically located at the apical rather than basolateral plasma membrane. An apical localization of the AC133 antigen was also observed in various human embryonic epithelia including the neural tube, gut, and kidney. Electron microscopy revealed that, within the apical plasma membrane of Caco-2 cells, the AC133 antigen was confined to microvilli and absent from the planar, intermicrovillar regions. This specific subcellular localization did not depend on an epithelial phenotype, because the AC133 antigen on hematopoietic stem cells, as well as that ectopically expressed in fibroblasts, was selectively found in plasma membrane protrusions. Hence, the human AC133 antigen shows the features characteristic of mouse prominin in epithelial and transfected non-epithelial cells, i.e. a selective association with apical microvilli and plasma membrane protrusions, respectively. Conversely, flow cytometry of murine CD34(+) bone marrow progenitors revealed the cell surface expression of prominin. Taken together, the data strongly suggest that the AC133 antigen is the human orthologue of prominin.

Cytochemical evidence that acetylcholine is a neurotransmitter of neurons that make excitatory and inhibitory outputs in the locust ocellar visual system

Three different cytochemical methods were used to detect acetylcholine in large, second-order neurons of locust ocelli (L-neurons). The first method used polyclonal antibodies raised against choline cleaved from acetylcholine and then conjugated with native protein, and this revealed strong staining for acetylcholine in axons whose number, size, and location indicated that they were of L-neurons. A corresponding staining pattern was found using the second method with a polyclonal antiserum against choline acetyltransferase (ChAT). The third method was the histochemical detection at the electron microscope level of acetylcholinesterase, the enzyme responsible for the breakdown of acetylcholine. We found that this enzyme is located in synaptic clefts of L-neurons in both of the brain regions where L-neurons are known to make excitatory and inhibitory output synapses. Acetylcholinesterase was confined to synaptic sites, which is consistent with a role in synaptic transmission at these synapses. Taken together, the findings suggest that L-neurons use acetylcholine as a neurotransmitter.

The performance of synapses that convey discrete graded potentials in an insect visual pathway

Synapses from nonspiking neurons transmit small graded changes in potential, but variability in their postsynaptic potential amplitudes has not been extensively studied. At synapses where the presynaptic signal is an all-or-none spike, the probabilistic manner of neurotransmitter release causes variation in the amplitudes of postsynaptic potentials. I have measured the reliability of the operation of synapses that convey small graded potentials between pairs of identified large, second-order neurons in the locust ocellar system. IPSPs are mediated by small rebound spikes, which are graded in amplitude, in the presynaptic neuron. A transfer curve plotting amplitudes of spikes against amplitudes of IPSPs has a characteristic S shape with a linear central portion where IPSP amplitude is between -0.2 and -0.6 as large as spike amplitude but shows appreciable scatter. Approximately half of the scatter is attributable to background noise, most of which originates in photoreceptors and persists in darkness. The remaining noise is intrinsic to the synapse itself and is usually 0.3-0.7 mV in amplitude. It limits the resolution with which two spike amplitudes can be distinguished from one another to approximately 2 mV and, because the linear part of the transfer curve occupies approximately 10 mV in spike amplitudes, limits the number of discrete signal levels that can be conveyed across the synapse to approximately five. The amplitude of the noise is constant throughout the synaptic operating range, which means it is unlikely that presynaptic membrane potential controls transmitter release by setting a single probability level for quantal release.

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.

PSGL-1-mediated adhesion of human hematopoietic progenitors to P-selectin results in suppression of hematopoiesis

Cellular interactions are critical for the regulation of hematopoiesis. The sialomucin PSGL-1/CD162 mediates the attachment of mature leukocytes to P-selectin. We now show that PSGL-1 also functions as the sole receptor for P-selectin on primitive human CD34+ hematopoietic progenitor cells (HPC). More importantly, ligation of PSGL-1 by immobilized or soluble ligand or anti-PSGL-1 antibody results in a profound suppression of HPC proliferation stimulated by potent combinations of early acting hematopoietic growth factors. These data demonstrate an unanticipated but extremely marked growth-inhibitory effect of P-selectin on hematopoiesis and provide direct evidence that PSGL-1, in addition to its well-documented role as an adhesion molecule on mature leukocytes, is a potent negative regulator of human hematopoietic progenitors.

Seeing what is coming: building collision-sensitive neurones

The image of a rapidly approaching object has to elicit a quick response. An animal needs to know that the object is approaching on a collision course and how imminent a collision is. The relevant information can be computed from the way that the image of the object grows on the retina of one eye. Firm data about the types of neurones that react to such looming stimuli and trigger avoidance reactions come from recent studies on the pigeon and the locust. The neurones responsible are tightly tuned to detect objects that are approaching on a direct collision course. In the pigeon these neurones signal the time remaining before collision whereas in the locust they have a crucial role in the simple strategy this animal uses to detect an object approaching on a collision course.

Cytoskeleton and integrin-mediated adhesion signaling in human CD34+ hemopoietic progenitor cells

Significant progress has been made recently in the understanding of cell adhesion signaling. Many components of focal adhesion complexes have been identified in fibroblasts and endothelial cells, showing considerable overlap and complementarity between growth signaling mediated by growth factor receptors and adhesive signaling mediated by cell adhesion receptors such as integrins. These studies showed that the cytoskeleton is essential for the correct intracellular localization of large signaling complexes that regulate the cellular machinery. Although adhesive interactions are essential to maintain steady-state hemopoiesis, the study of the function and role of adhesive interactions in hemopoietic progenitor and stem cells is less advanced. As in fibroblasts, functional overlap between hemopoietic growth factor receptors and cell adhesion receptors has been demonstrated, with the cytoskeleton likely playing a critical role in integrating information provided by soluble factors and cell adhesion molecules constituting the hemopoietic microenvironment. The intention of this article is to give a critical review of the current knowledge about the cytoskeleton and integrin-mediated signaling in hemopoietic progenitor cells.

Prolonged release and c-kit expression of haemopoietic precursor cells mobilized by stem cell factor and granulocyte colony stimulating factor

Mobilization of haemopoietic precursor cells into the circulation by the combination of cytokines, stem cell factor (SCF) and G-CSF in previously untreated patients with carcinoma of the breast resulted in increased yield of collected peripheral blood precursor cells (PBPC). This mobilization of PBPC by SCF with G-CSF lasted several days after ceasing the cytokines in comparison to the rapid fall of PBPC after ceasing G-CSF. Possible mechanisms for this increased and prolonged mobilization were investigated. Immunological phenotyping with CD38, Thy-1 and MDR-1 of the CD34-positive mobilized PBPC detected no difference in maturity compared to PBPC mobilized by G-CSF alone. However, the down-regulation of c-kit, which is associated with the mechanism of mobilization, was much greater in the PBPC mobilized by SCF and G-CSF. The potential clinical implication of increased and prolonged mobilization is increased yield, allowing transplantation of heavily pre-treated patients, transplantation with PBPC from a single apheresis, or PBSC support for multiple courses of high-dose therapy from one mobilization procedure.

Differential cell surface expression of the STRO-1 and alkaline phosphatase antigens on discrete developmental stages in primary cultures of human bone cells

Human osteoblast-like cells can be readily cultured from explants of trabecular bone, reproducibly expressing the characteristics of cells belonging to the osteoblastic lineage. Dual-color fluorescence-activated cell sorting was employed to develop a model of bone cell development in primary cultures of normal human bone cells (NHBCs) based on the cell surface expression of the stromal precursor cell marker STRO-1 and the osteoblastic marker alkaline phosphatase (ALP). Cells expressing the STRO-1 antigen exclusively (STRO-1+/ALP-), were found to exhibit qualities preosteoblastic in nature both functionally by their reduced ability to form a mineralized bone matrix over time, as measured by calcium release assay, and in the lack of their expression of various bone-related markers including bone sialoprotein, osteopontin, and parathyroid hormone receptor based on reverse trancriptase polymerase chain reaction (PCR) analysis. The majority of the NHBCs which expressed the STRO-1-/ALP+ and STRO-1-/ALP- phenotypes appeared to represent fully differentiated osteoblasts, while the STRO-1+/ALP+ subset represented an intermediate preosteoblastic stage of development. All STRO-1/ALP NHBC subsets were also found to express the DNA-binding transcription factor CBFA-1, confirming that these cultures represent committed osteogenic cells. In addition, our primer sets yielded four distinct alternative splice variants of the expected PCR product for CBFA-1 in each of the STRO-1/ALP subsets, with the exception of the proposed preosteoblastic STRO-1+/ALP- subpopulation. Furthermore, upon re-culture of the four different STRO-1/ALP subsets only the STRO-1+/ALP- subpopulation was able to give rise to all of the four subsets yielding the same proportions of STRO-1/ALP expression as in the original primary cultures. The data presented in this study demonstrate a hierarchy of bone cell development in vitro and facilitate the study of bone cell differentiation and function.

Osteoclast-mediated bone resorption is stimulated during short-term administration of granulocyte colony-stimulating factor but is not responsible for hematopoietic progenitor cell mobilization

The cellular and molecular mechanisms responsible for hematopoietic progenitor cell (HPC) mobilization from bone marrow (BM) into peripheral blood after administration of cytokines such as granulocyte colony-stimulating factor (G-CSF) are still unknown. In this study we show that high concentrations of soluble calcium induce the detachment of BM CD34(+) HPC adherent on fibronectin, a major component of BM extracellular matrix. Because G-CSF has been shown to induce osteoporosis in patients with congenital neutropenia and in G-CSF-overexpressing transgenic mice, we hypothesized that short-term G-CSF administration may be sufficient to induce bone resorption, resulting in the release of soluble calcium in the endosteum leading in turn to the inhibition of attachment to fibronectin and the egress of HPC from the BM. We show herein that in humans, serum osteocalcin concentration, a specific marker of bone formation, is strongly reduced after 3 days of G-CSF administration. Furthermore, in patients mobilized with G-CSF either alone or in association with stem cell factor or interleukin-3, the reduction of serum osteocalcin is significantly correlated with the number of HPC mobilized in peripheral blood. Urine levels of deoxypyridinoline (DPyr), a specific marker of bone resorption, gradually elevated during the time course of G-CSF administration until day 7 after cessation of G-CSF, showing a simultaneous stimulation of bone degradation during G-CSF-induced HPC mobilization. In an in vivo murine model, we found that the number of osteoclasts was dramatically increased paralleling the elevation of DPyr after G-CSF administration. When pamidronate, an inhibitor of osteoclast-mediated bone resorption, was administered together with G-CSF in mice, the G-CSF-induced increase of DPyr levels was completely abolished whereas the numbers of colony-forming cells mobilized in peripheral blood were not decreased, but unexpectedly increased relative to the numbers elicited by G-CSF alone. Collectively, our data therefore show that short-term administration of G-CSF induces bone degradation by a simultaneous inhibition of bone formation and an enhanced osteoclast-mediated bone resorption. This increased bone resorption is inhibited by pamidronate without reducing G-CSF-induced HPC mobilization, suggesting that the activation of bone resorption after G-CSF administration is not the direct cause of HPC mobilization as initially hypothesized, but a parallel event.

Granulocyte colony-stimulating factor (G-CSF) dose-dependent efficacy in peripheral blood stem cell mobilization in patients who had failed initial mobilization with chemotherapy and G-CSF

For 10 consecutive patients in our unit who did not show a significant rise in blood progenitor cells within 14 days following chemotherapy and G-CSF, we increased the G-CSF dose from 5 to 10 microg/kg/day (n = 9) or from 10 to 15 microg/kg/day (n = 1). As a result, there were significant increases in total yield as well as yield per apheresis of mononuclear cells, CD34+ cells and CFU-GM (P < 0.025, <0.01 and <0.005, respectively). After G-CSF dose escalation, six of the 10 patients had sufficient CD34+ cells for performing transplantation. These results demonstrate a dose-dependent response of progenitor cell mobilization by G-CSF when used in combination with chemotherapy. Moreover, increasing the dose of G-CSF as late as the third week of mobilization may still provide sufficient cell yield even with patients who did not show a significant mobilization with conventional doses of G-CSF.

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.

Stem cell factor as a single agent induces selective proliferation of the Philadelphia chromosome positive fraction of chronic myeloid leukemia CD34(+) cells

The interaction between p145(c-KIT) and p210(bcr-abl) in transduced cell lines, and the selective outgrowth of normal progenitors during long-term culture of chronic myeloid leukemia (CML) cells on stroma deficient in stem-cell factor (SCF) suggests that the response of CML cells to SCF may be abnormal. We examined the proliferative effect of SCF(100 ng/mL), provided as the sole stimulus, on individual CD34(+) cells from five normal donors and five chronic-phase CML patients. Forty-eight percent of isolated single CML CD34(+) cells proliferated after 6 days of culture to a mean of 18 cells, whereas only 8% of normal CD34(+) cells proliferated (mean number of cells generated was 4). SCF, as a single agent, supported the survival and expansion of colony-forming unit-granulocyte-macrophage (CFU-GM) from CML CD34(+)CD38(+) cells and the more primitive CML CD34(+)CD38(-) cells. These CFU-GM colonies were all bcr-abl positive, showing the specificity of SCF stimulation for the leukemic cell population. Coculture of CML and normal CD34(+) cells showed exclusive growth of Ph+ cells, suggesting that growth in SCF alone is not dependent on secretion of cytokines by CML cells. SCF augmentation of beta1-integrin-mediated adhesion of CML CD34(+) cells to fibronectin was not increased when compared with the effect on normal CD34(+) cells, suggesting that the proliferative and adhesive responses resulting from SCF stimulation are uncoupled. The increased proliferation may contribute to the accumulation of leukemic progenitors, which is a feature of CML.

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.

Dual control by divalent cations and mitogenic cytokines of alpha 4 beta 1 and alpha 5 beta 1 integrin avidity expressed by human hemopoietic cells

Beta-1 integrins have essential functions in hemopoietic and immune systems by controlling phenomenons such as cell homing and cell activation. The function alpha 4 beta 1 and alpha 5 beta 1 integrins is regulated by divalent cations and, as demonstrated more recently, by mitogenic cytokines which activate them by "inside-out" mechanisms. Using the adhesive interaction of a cytokine-dependent human hemopoietic cell line to immobilized fibronectin, we have analyzed the requirements in divalent cations Mn2+, Mg2+ and Ca2+ for alpha 4 beta 1 and alpha 5 beta 1 activation by "inside-out" mechanisms triggered by cytokines such as granulocyte-macrophage colony stimulating factor or KIT ligand, or by external conformational constraints with the function-activating anti-beta 1 integrin monoclonal antibody 8A2. The intrinsic difference between these two modes of beta 1 integrin activation was revealed by their different requirements in divalent cations. We found that in the absence of any divalent cations, alpha 4 beta 1 and alpha 5 beta 1 were non-functional even after further stimulation by cytokines or 8A2. However, whilst either Ca2+, Mg2+ or Mn2+ were able to restore adhesive functions of alpha 4 beta 1 and alpha 5 beta 1 when activated by 8A2, only Mg2+ and Mn2+ were able to support activation of alpha 4 beta 1 and alpha 5 beta 1 by cytokines. Furthermore, high concentrations of Ca2+ exceeding 20 mM dramatically inhibited cell adhesion to fibronectin induced by Mn2+ and cytokines but not by 8A2. On the contrary, in the presence of both Ca2+ and Mg2+, Mn2+ had an additive effect on the activation of alpha 4 beta 1 and alpha 5 beta 1 by mitogenic cytokines. The presence of the absence of these divalent cations did not inhibit early tyrosine phosphorylation induced by the binding of KIT ligand to its tyrosine-kinase receptor KIT. Therefore, we propose that in hemopoietic cells, Ca2+, Mg2+ and Mn2+ may modulate in vivo alpha 4 beta 1 and alpha 5 beta 1 regulation by mitogenic cytokines, a phenomenon involved in the regulation of hemopoietic progenitor cell homing within the bone marrow.

Local circuit for the computation of object approach by an identified visual neuron in the locust

The lobula giant movement detector (LGMD) neuron in the locust visual system is part of a motion-sensitive pathway that detects objects approaching on a collision course. Here we show that the retinotopic units presynaptic to the LGMD make synapses directly with each other and these synapses are immediately adjacent to their outputs onto the LGMD. Synapses occur along the fine dendrites of the LGMD in the distal lobula, often in large numbers and completely covering the LGMD processes. Gamma aminobutyric acid (GABA) was eliminated as a possible neurotransmitter at these synapses when immunogold-tagged monoclonal GABA antibody did not specifically label the afferent processes. We used a histochemical method to demonstrate that acetylcholine esterase, the enzyme that hydrolyses acetylcholine at cholinergic synapses, was present in the synaptic clefts between the retinotopic units and along the membrane of the LGMD. It is well established that acetylcholine has both excitatory and inhibitory effects and we propose that these retinotopic units excite the LGMD, but inhibit each other; and that the synapses form the substrate for a critical race between excitation caused by edges moving out over successive photoreceptors, and inhibition spreading laterally. This results in the selective response to objects approaching on a collision course.

Identification and isolation of candidate human keratinocyte stem cells based on cell surface phenotype

Despite the central role of human epidermal stem cells in tissue homeostasis, wound repair, and neoplasia, remarkably little is known about these cells, largely due to the absence of molecular markers that distinguish them from other proliferative cells within the germinative/basal layer. Epidermal stem cells can be distinguished from other cells in the basal layer by their quiescent nature in vivo and their greater overall proliferative capacity. In this study, we demonstrate enrichment and isolation of a subpopulation of basal epidermal cells from neonatal human foreskin based on cell surface phenotype, which satisfy these criteria. These putative stem cells are distinguished from other basal cells by their characteristic expression of high levels of the adhesion molecule alpha6, a member of the integrin family (alpha6bri), and low levels of a proliferation-associated cell surface marker recognized by recently described mAb 10G7 (10G7(dim)). We conclude that cells with the phenotype alpha6bri10G7(dim) represent the epidermal stem cell population based on the demonstration that these cells (i) exhibit the greatest regenerative capacity of any basal cells, (ii) represent a minor subpopulation (approximately 10%) of immature epidermal cells, which (iii) are quiescent at the time of isolation from the epidermis, as determined by cell cycle analysis.

MUC18, a member of the immunoglobulin superfamily, is expressed on bone marrow fibroblasts and a subset of hematological malignancies

Despite the importance of bone marrow stromal cells in hemopoiesis, the profile of surface molecule expression is relatively poorly understood. Mice were immunized with cultured human bone marrow stromal cells in order to raise monoclonal antibodies to novel cell surface molecules, which might be involved in interactions with hemopoietic cells. Three antibodies, WM85, CC9 and EB4 were produced, and were found to identify a 100-110 kDa antigen on bone marrow fibroblasts. Molecular cloning revealed the molecule to be MUC18 (CD146), a member of the immunoglobulin superfamily, previously described as a marker of metastatic melanoma. In addition to the expected expression on melanoma cell lines and endothelial cells, a number of human leukemic cell lines were found to express MUC18, including all six T leukemia lines tested, one of five B lineage lines and one of four myeloid lines. Analysis of bone marrow samples from patients revealed positivity in 20% of B lineage ALL (n = 20), one of three T-ALL, 15% of AML (n = 13) and 43% of various B lymphoproliferative disorders (n = 7). No apparent reactivity was observed with mononuclear cells from normal peripheral blood or bone marrow, including candidate hemopoietic stem cells characterized by their expression of the CD34 antigen. However, positive selection of bone marrow mononuclear cells labeled with MUC18 antibody revealed a rare subpopulation (<1%) containing more than 90% of the stromal precursors identified in fibroblast colony-forming assays. The structure and tissue distribution of MUC18 suggest a functional role in regulation of hemopoiesis.

Ex vivo culture of peripheral blood CD34+ cells: effects of hematopoietic growth factors on production of neutrophilic precursors

A major potential application for ex vivo culture of hematopoietic progenitor cells is the treatment of cytopenia following high-dose chemotherapy and hematopoietic transplantation. We have previously postulated that infusion of a sufficient number of neutrophil postprogenitor cells generated by ex vivo culture of CD34+ cells may be able to abrogate neutropenia. In this article, we describe further development of an efficient stromal-free, cytokine-dependent, static culture system for generation of these cells. Our previous studies indicated that maximal production of nucleated cells and myeloid progenitor cells from PB CD34+ cells occurred with multiple hematopoietic growth factor (HGF), notably the 6-HGF combination of interleukin (IL)-1, IL-3, IL-6, granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage-CSF (GM-CSF), and stem cell factor (SCF). In the present study, we determine the contribution of each of these 6 HGF in generation of neutrophilic precursors. SCF, G-CSF, and IL-3 were found to be the most important HGF for production of neutrophilic cells. The 4-HGF combination of IL-3, IL-6, G-CSF, and SCF was optimized by performing dose-response experiments and shown to be as potent as 6 HGF for production of nascent CFU-GM and neutrophilic precursors.

Increased recruitment of hematopoietic progenitor cells underlies the ex vivo expansion potential of FLT3 ligand

The ligand for flt-3 (FLT3L) exhibits striking structural homology with stem cell factor (SCF) and monocyte colony-stimulating factor (M-CSF) and also acts in synergy with a range of other hematopoietic growth factors (HGF). In this study, we show that FLT3L responsive hematopoietic progenitor cells (HPC) are CD34+CD38-, rhodamine 123dull, and hydroperoxycyclophosphamide (4-HC) resistant. To investigate the basis for the capacity of FLT3L to augment the de novo generation of myeloid progenitors from CD34+CD38- cells, single bone marrow CD34+CD38- cells were sorted into Terasaki wells containing serum-free medium supplemented with interleukin-3 (IL-3), IL-6, granulocyte colony-stimulating factor (G-CSF), SCF (4 HGF) +/- FLT3L. Under these conditions, FLT3L recruited approximately twofold more CD34+CD38- cells into division than 4 HGF alone. The enhanced proliferative response to FLT3L was evident by day 3 and was maintained at all subsequent time points examined. In accord with these findings, we also show that transduction of CD34+CD38- cells with the LAPSN retrovirus is enhanced by FLT3L. The results of these experiments therefore indicate that increased recruitment of primitive HPC into cell cycle underlies the ex vivo expansion potential of FLT3L and also its ability to improve retroviral transduction of HPC.

Adhesion molecules in haemopoiesis

In the adult mammal, haemopoiesis is restricted to the extravascular compartment of the bone marrow (BM) where primitive haemopoietic stem cells (HSC) and their clonogenic progeny develop in intimate contiguity with a heterogeneous population of stromal cells that comprise the haemopoietic micro-environment (HM). Although the importance of cellular interactions between primitive haemopoietic progenitor cells (HPC) and marrow stromal cells is well established, precise definition of the nature of many of these interactions at the molecular level is lacking and remains an objective of fundamental importance to understanding of haemopoietic regulation. Current data suggest that a wide variety of cell surface molecules representing several adhesion molecule superfamilies, including integrins, selectins, sialomucins and the immunoglobulin gene superfamily, are involved in supporting cell-cell and cell-extracellular matrix (ECM) interactions. These diverse CAM-ligand interactions, rather than simply serving to initiate and maintain contact between HPC and stromal cells and ECM components, also have an additional, more direct role in controlling the growth and development of primitive haemopoietic cells.

Integrin expression and function on human osteoblast-like cells

The integrin family of cell adhesion molecules are a series of cell surface glycoproteins that recognize a range of cell surface and extracellular matrix (ECM)-associated ligands. To date, the precise role of individual integrin molecules in bone cell-ECM interactions remains unclear. Cell binding assays were performed to examine the ability of normal human bone cells (NHBCs) to adhere to different ECM proteins in vitro. NHBCs displayed preferential adhesion to fibronectin over collagen types I, IV, and vitronectin and showed low affinity binding to laminin and collagen type V. No binding was observed to collagen type III. The integrin heterodimers alpha 1 beta 1, alpha 2 beta 1, alpha 3 beta 1, alpha 5 beta 1, alpha v beta 3, and alpha v beta 5 were found to be constitutively expressed on the cell surface of NHBCs by flow cytometric analysis. The integrins alpha 4 beta 1 and alpha 6 beta 1 were not expressed by NHBCs. Subsequent binding studies showed that NHBC adhesion to collagen and laminin was mediated by multiple integrins where cell attachment was almost completely inhibited in the presence of a combination of function-blocking monoclonal antibodies (Mabs) to alpha 1 beta 1, alpha 2 beta 1, alpha 3 beta 1, and beta 1. In contrast, the adhesion of NHBCs to fibronectin was only partially inhibited (50%) in the presence of blocking Mabs to alpha 3 beta 1, alpha 5 beta 1, and beta 1. The attachment of NHBCs to collagen, laminin, fibronectin, and vitronectin was also found to be unaffected in the presence of a function-blocking Mab to alpha v beta 3. The results of this study indicate that beta 1 integrins appear to be the predominant adhesion receptor subfamily utilized by human osteoblast-like cells to adhere to collagen and laminin and in part to fibronectin.

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.

Expression of the Wilms' tumor gene (WT1) in normal hemopoiesis

The Wilms tumor suppressor gene (WT1) is mutated in a number of cases of Wilms' tumor as well as in mesothelioma and leukemia. It encodes a transcription factor derived from any one of four alternate transcripts. WT1 has a restricted pattern of expression within the body and within the hemopoietic system its expression is limited to primitive leukemias and a number of leukemic cell lines. Given the overexpression of WT1 in leukemias, we have addressed the question of whether this gene is expressed within the normal hemopoietic system. Mononuclear bone marrow (BM) cells obtained from normal donors were separated by fluorescence-activated cell sorting (FACS) into "primitive" (CD34+) and "mature" (CD34-) cell populations. Total RNA extracted from these cells was subjected to reverse transcriptase polymerase chain reaction (RT-PCR) using primers based on the WT1 sequence, to examine the expression of this gene within the hemopoietic system. Phenotypic purity of cells was guaranteed by performing single-cell sorting followed by RT-PCR to define the precise cellular phenotypes that express WT1. Expression of WT1 was detected in cells bearing the CD34+ phenotype but not in those cells lacking expression of CD34. In addition, single-cell analysis revealed that expression of WT1 occurred in the candidate stem cell-containing population of hemopoietic cells which have the phenotype CD34+ CD38-. Moreover, the single-cell RT-PCR analysis also demonstrated that differential expression of alternate transcripts of WT1 occurs between hemopoietic progenitor cells with the same phenotype. In conclusion, expression of WT1 is limited to early progenitors of the blood system, which suggests that this gene plays a critical role in hemopoietic development.

Signaling of object approach by the DCMD neuron of the locust

The locust descending contralateral motion detector (DCMD) responds to movements anywhere within a wide visual field, but responds most strongly to the images of approaching objects. It has been claimed that the response peaks before the end of an approach movement, providing a signal that anticipates collision. However, we find that when the locust eye is presented with appropriate computer-generated images of approaching objects, the response builds up until after movement has stopped. Premature peaking in the response is due to failure to stimulate the eye with sufficiently small and frequent jumps in image edges. We conclude that the DCMD signals impending collision by tracking edge motion throughout object approach.

Specificity and functional effects of antibodies to human stem cell factor

Three monoclonal antibodies (Mabs), 7H6, 4B10 and Genzyme Mab, and a commercially-available polyclonal antiserum (Genzyme) to human Stem Cell Factor (SCF) were compared for their ability to detect native and recombinant SCF in a variety of assays, and for blocking of SCF function. All antibodies were found to bind to the membrane bound isoform as well as soluble SCF and to bind to both glycosylated (yeast MGF) and unglycosylated (E. coli SCF) recombinant factor. Mabs 7H6 and 4B10, as well as the polyclonal antiserum could immunoprecipitate membrane-associated SCF and all the antibodies could detect recombinant soluble SCF on western blots, although the binding of all except 7H6 was partially sensitive to reduction. Titration of the antibodies on CHO cells expressing membrane-associated human SCF showed similar dose-dependence for all Mabs with 70% of maximum binding seen at 3, 5 and 8 micrograms/ml for 7H6, 4B10 and Genzyme Mab respectively, however the maximum binding seen with 7H6 was approximately 2-fold greater than with 4B10 and 7-fold greater than Genzyme Mab. Competitive binding experiments of the Mabs on cells expressing membrane SCF gave non-reciprocal blocking in all cases with 7H6 completely blocking 4B10 and Genzyme Mab binding. All antibodies except the Genzyme Mab effectively blocked SCF binding to c-Kit-expressing cells, and were strongly inhibitory in an assay of in vitro haemopoiesis which is believed to depend on adhesive interactions, as well as the "classical' cytokine-receptor interaction, mediated by SCF binding to c-Kit.

Cytokine regulation of proliferation and cell adhesion are correlated events in human CD34+ hemopoietic progenitors

Adhesive interactions with the extracellular matrix of the bone marrow (BM) stroma are of critical importance in the regulation of hematopoiesis. In part, these interactions are presumed to play an important role in retaining CD34+ hematopoietic progenitor cells (HPCs) within the BM environment, in close proximity with BM stromal cells and the cytokines they produce. Evidence of a more direct role for cell adhesion in the regulation of hematopoiesis is provided by recent data showing that adhesive interactions can also provide important costimulatory signals. We have previously shown that normal CD34+ HPCs express high levels of fibronectin (Fn) receptors very late antigen-4 (VLA-4) and VLA-5 in a low-affinity state, which do not allow HPCs to strongly adhere on immobilized Fn, and that cytokines such as interleukin-3, granulocyte-monocyte colony-stimulating factor, and stem cell factor transiently activate these receptors, providing HPCs with an adhesive phenotype on Fn. Thus, knowledge of the functional states of adhesion receptors is critical to our understanding of the physiological mechanisms responsible for the regulation of normal hematopoiesis. Herein, we show that combinations of cytokines that synergize to stimulate the proliferation of CD34+ HPCs result in additive stimulation of the adhesion of these cells to Fn. Thus, the activation level of Fn receptors expressed by normal CD34+ HPCs is highly correlated with their proliferative state, suggesting a functional link between these two events. Therefore, we propose a 2-step model with an initial activation of VLA-4 and VLA-5 generated by cytokine receptors that is followed by a secondary signal resulting from Fn binding to VLA-4 and VLA-5, which may cooperate with those generated by cytokine receptors.

The biology and application of human bone marrow stromal cell precursors

The importance of the stromal tissue of the bone marrow in regulating hemopoiesis is well documented. However, several features of marrow stromal cell biology remain poorly understood, in particular, the ontogeny and phylogeny of the various stromal elements that comprise the microenvironment of the bone marrow. In this article we review recent data concerning the immunophenotype and functional characteristics of precursor cells for marrow stromal tissue. The study of these stromal precursor cells (SPC) represents an exciting new field of research that will almost certainly expand in the future as we gain a greater understanding of the cellular and molecular events, environmental cues, and growth factors that physiologically regulate the commitment and subsequent development of SPC. Although the field of marrow SPC biology is in its infancy, we predict that future studies will result in several novel clinical applications for SPC. We, therefore, conclude this article by speculating on a number of these potential applications and, thus, view SPC and their progeny as likely vehicles for several novel and important cellular therapies, including gene therapy.

A powerful new technique for isolating genes encoding cell surface antigens using retroviral expression cloning

cDNA expression cloning using retroviral vectors provides a means of stably introducing genes into target cells at efficiencies that surpass those achieved by transfection. Furthermore, retroviral vectors allow for the introduction and expression of complex cDNA libraries in a wide range of cell types, including cells of hemopoietic origin. Here we report a novel method for rapidly isolating genes encoding cell surface molecules (CSM) from a human bone marrow stromal cell cDNA library constructed in the retroviral vector, pRUFneo. With a newly described, highly efficient selection strategy using mAb and Ab-coated magnetic beads, we have successfully isolated six cDNA encoding previously defined CSM, including beta 1 integrin and endoglin. Moreover, we have used this approach to define the gene and hence the CSM identified by three previously unclustered mAb. These results confirm previous studies demonstrating the general utility of retroviral cDNA libraries and further extend their use to the expression cloning of cDNA encoding CSM.

A powerful new technique for isolating genes encoding cell surface antigens using retroviral expression cloning

cDNA expression cloning using retroviral vectors provides a means of stably introducing genes into target cells at efficiencies that surpass those achieved by transfection. Furthermore, retroviral vectors allow for the introduction and expression of complex cDNA libraries in a wide range of cell types, including cells of hemopoietic origin. Here we report a novel method for rapidly isolating genes encoding cell surface molecules (CSM) from a human bone marrow stromal cell cDNA library constructed in the retroviral vector, pRUFneo. With a newly described, highly efficient selection strategy using mAb and Ab-coated magnetic beads, we have successfully isolated six cDNA encoding previously defined CSM, including beta 1 integrin and endoglin. Moreover, we have used this approach to define the gene and hence the CSM identified by three previously unclustered mAb. These results confirm previous studies demonstrating the general utility of retroviral cDNA libraries and further extend their use to the expression cloning of cDNA encoding CSM.