Measurement of the growth parameters of precursor B-acute lymphoblastic leukaemic cells in co-culture with bone marrow stromal cells; detection of two cd10 positive populations with different proliferative capacities and survival

Chromosome social distancing and crowd control: the dual role of Ki67

The Ki67 protein is proposed to have two conformations; one which segregates chromosomes before anaphase, and the other which results in chromosome condensation after cell division to exclude large cytosolic components from the reforming nuclei of daughter cells.

Tracking chondrocytes and assessing their proliferation with carboxyfluorescein diacetate succinimidyl ester: effects on cell functions

Distinguishing between implanted and host-derived cells, as well as cells of different phenotypes, is important in determining mechanisms of cell-based repair of cartilage. The objectives of this study were to assess the utility of carboxyfluorescein diacetate, succinimidyl ester ("CFDA, SE" or CFSE) for tracking chondrocytes from superficial (S) and middle (M) zones and their proliferation, and to determine the effects of CFSE on the chondrocyte functions, proliferation, and synthesis of proteoglycan 4 (PRG4) and glycosaminoglycan (GAG). CFSE-labeled and unlabeled S and M zone chondrocytes were plated in either low- or high-density (10,000 or 200,000 cells/cm(2)) monolayer, incubated, and analyzed on days 1 and 7. Cell suspensions were analyzed for retention of CFSE by flow cytometry and fluorescence microscopy and for cell proliferation by assay for DNA and GAG. Cultures were also analyzed for newly synthesized PRG4. Deconvolution of flow cytometric histograms was done to determine the number of cells in each doubling generation. Most chondrocytes were labeled consistently and intensely labeled with CFSE through 10 cycles of division. At day 7 of culture, approximately 95% of S and M zone cells seeded at high density could be distinguished as fluorescent. Chondrocyte proliferation and synthesis of PRG4 were unaffected by cell labeling, while GAG synthesis was slightly diminished. CFSE may be useful in determining the fate and function of implanted chondrocytes in vivo.

Tracking antigen-driven responses by flow cytometry: monitoring proliferation by dye dilution

Cell-tracking reagents such as the green-fluorescent protein labeling dye CFSE and the red-fluorescent lipophilic membrane dye PKH26 are commonly used to monitor cell proliferation by flow cytometry in heterogeneous cell populations responding to immune stimuli. Both reagents stain cells with a bright homogeneous fluorescence, which is partitioned between daughter cells during each cell division. Because daughter cell fluorescence intensities are approximately halved after each division, the intensity of a cell relative to its intensity at the time of staining provides information about how many divisions it has undergone. Knowing how many rounds of division have occurred and the relative number of cells in each daughter generation, one can back-calculate the number of cells in the original population (i.e., cells present at the time of stimulus) that went on to respond by proliferating. Using this information, the precursor cell frequencies and extent of expansion to a specific antigen or mitogen of interest can be calculated. Concurrently, the phenotype of the cells can be determined, as well as their ability to bind antigen or synthesize cytokines, providing more detailed characterization of all cells responding to the antigen, not just effector cells. In multiparameter flow cytometric experiments to simultaneously analyze antigen-specific tetramer binding, cytokine production and T-cell proliferation, we found that only approximately half of the cells that exhibited specific binding to influenza tetramer also proliferated, as measured by dye dilution, and synthesized IFNgamma in response to antigen. We expect the advent of new cell tracking dyes emitting from the violet to the near infrared combined with the increasing number of lasers and detectors on contemporary flow cytometers to further expand the usefulness of this approach to characterization of complex antigen-driven immunological responses.

Cell tracking 2007: a proliferation of probes and applications

The articles in this thematic issue, entitled "Tracking Cell Proliferation and Function," illustrate some of the choices made by authors pushing the envelope for cell tracking applications in their areas of interest. Over the past decade there has been a proliferation in the range of commercially available probes for these studies, the capabilities of the instrumentation used to detect them, and in the biological systems being studied. This introductory to the thematic issue presents the advantages and limitations of the more commonly used probes such as CFSE and PKH26, as well as emerging probes that expand the range of fluorescence available, including quantum dots and the new CellVue dyes. Appropriate method and instrument setup controls and possible data analysis strategies are discussed with the goal of urging experienced investigators to include all critical information and controls when publishing their data and of aiding researchers new to cell tracking to make informed decisions on which cell tracking reagent(s) are best suited for their particular application. All cell tracking assays have the common goal of determining the fate of a particular cell population within a heterogeneous environment, whether in vivo or in vitro. Some of the common themes among the contributions found in this issue include how various probes are used to track (i) cell proliferation, (ii) regulatory and effector immune cell function and (iii) membrane transfer and antigen presentation. Although these represent only a small fraction of the large and growing list of applications for cell tracking, clearly illustrate the growing trend toward the use of multiple tracking reagents and multiple detection modalities to address complex biological questions.

Early myeloid cells expressing c-KIT isoforms differ in signal transduction, survival and chemotactic responses to Stem Cell Factor

Isoforms of the receptor tyrosine kinase, c-KIT, differ in the presence or absence of a GNNK tetrapeptide in the extracellular juxtamembrane region. When expressed in murine NIH3T3 cells, these isoforms of c-KIT showed differential activation of signaling pathways and proliferation in response to Stem Cell Factor (SCF). However, c-KIT is not normally expressed by fibroblasts, but plays a key role in hematopoiesis. Because signaling pathways and cellular responses mediated by c-KIT differ in different cell types, we studied the effects of SCF stimulation on factor-dependent murine early myeloid cells expressing human GNNK+ or GNNK- c-KIT. As in fibroblasts, SCF activation of the GNNK- isoform resulted in stronger, more rapid receptor phosphorylation, and activation of Src kinases, while only a minor effect on the phosphatidylinositol 3-kinase pathway was observed. Similarly, more rapid Src kinase-dependent internalisation of the GNNK- isoform occurred in response to SCF. In contrast to fibroblasts, only minor differences in ERK activation were seen indicating that early hematopoietic cells, unlike fibroblasts, are not dependent on Src kinases for activation of this pathway in response to SCF. Enhanced SCF-dependent growth was observed in GNNK- c-KIT expressing cells due to lower cell attrition. The rate of cell division was similar. Importantly, cells expressing the GNNK- isoform showed a greater chemotactic response to SCF.

Tracking chondrocytes and assessing their proliferation with PKH26: effects on secretion of proteoglycan 4 (PRG4)

Distinguishing between implanted and host-derived cells, as well as between distinct cell phenotypes, would be useful in assessing the mechanisms of cell-based repair of cartilage. The fluorescent tracker dye, PKH26, was previously applied to several cell types to assess proliferation in vitro and to track cells in vivo. The objectives of this study were to assess the utility of PKH26 for tracking chondrocytes from superficial and middle zones and their proliferation, and determine the effects of PKH26 on chondrocyte functions, in particular, proliferation and secretion of Proteoglycan 4 (PRG4). PKH26-labeled and unlabeled superficial and middle zone chondrocytes were plated in either low- or high-density monolayer culture and analyzed for retention of PKH26 by flow cytometry and fluorescence microscopy at days 0 and 7. Cell suspensions and conditioned media were analyzed for DNA and secretion of PRG4, respectively. Flow cytometric histograms were deconvolved so that the number of cells in each doubling generation contributing to the final cell population could be estimated. Chondrocytes were consistently and intensely labeled with PKH26 through 7 cycles of division. At day 7 of culture, >97% of superficial zone cells seeded at low or high density could be distinguished as fluorescent, as could middle zone cells seeded at high density. Retention of cell fluorescence after PKH26 labeling and lack of adverse effects on cell proliferation and synthesis of PRG4 suggest that PKH26 can be useful in determining the fate and function of implanted chondrocytes in vivo, as well as monitoring proliferation in vitro.

Cell division rates of primary human precursor B cells in culture reflect in vivo rates

Bone marrow stroma-based cultures provide a powerful model for studying cell division and apoptosis of primary human precursor B cells. Studies using this model are elucidating the mechanisms by which stromal cells inhibit apoptosis of cultured normal precursor B cells and have demonstrated that the apoptotic rate of cultured leukemic precursor B cells can predict clinical outcome in acute lymphoblastic leukemia. In contrast to apoptosis, cell division in this model has not been well characterized. In this study, we quantified the rates of cell division in cultured primary human normal and leukemic precursor B cells by labeling precursor B cells with the fluorescent dye carboxyfluorescein diacetate, succinimyl ester. Based on the rate of decreasing fluorescent signal over 3 weeks, normal CD19(+), CD10(+) precursor B cells divided once every 90.5 hours, a number that correlates well with the known in vivo rate of 65.5 hours. The division rates were similar among different cultures and constant throughout the 3 weeks of culture, suggesting that the variable expansions of precursor B cells seen among different samples and culture durations are not secondary to different cell division rates. Unlike normal cells, cultured leukemic B cells had a heterogeneous division rate that ranged from once every 26-240 hours. These rates correlated well with their respective in vivo proliferation index. These findings indicate that the stroma-based cultures faithfully replicate in vivo cell division rates and can be used to elucidate the pathways that regulate cell division of primary human precursor B cells.

Immune monitoring in xenotransplantation: the multiparameter flow cytometric mixed lymphocyte culture assay

Xenotransplantation requires monitoring of complex cellular interactions in vitro. A tool to monitor cell proliferation in detail would be instrumental in understanding these cellular interactions in heterogeneous xenogeneic lymphocyte cultures and in patients after xenotransplantation. To accomplish this, we used a fluorescent cell proliferation marker, 5,6-carboxyfluorescein diacetate succinimidyl ester (CFSE), in combination with flow cytometry. CFSE, a green fluorescent molecule, binds covalently to intracellular macromolecules. Each cell division reduces the fluorescent intensity per cell by half and shows a characteristic multipeak pattern in flow cytometric analysis. For this study, human lymphocytes were labeled with CFSE and cultured in the presence of irradiated porcine lymphocytes. Cell proliferation was detected in CFSE-labeled lymphocytes in both a single and a multiparameter flow cytometry setting. Concurrently, tritiated ((3)H) thymidine incorporation, a common method to measure gross cell proliferation, was assessed. The kinetics of CFSE-labeled cell proliferation correlated with (3)H-thymidine incorporation in that both methods showed a lag phase for days 1-3 and a log phase for days 4-7. Multiparameter flow cytometric monitoring of mixed lymphocyte cultures allowed phenotyping and assessment of viability of proliferating populations in heterogeneous xenogeneic stimulated human lymphocyte cultures and complemented the classical (3)H-thymidine incorporation assay. The use of this technique will allow a wide array of immunologic parameters to be measured in a heterogeneous xenogeneic mixed lymphocyte culture. The information gained from these assays is essential to understanding the biological significance of xenogeneic cellular interaction and for monitoring the immune status of the xenotransplanted patient.

Phototoxicity of the fluorescent membrane dyes PKH2 and PKH26 on the human hematopoietic KG1a progenitor cell line

BACKGROUND

The phototoxic effects of the well-known fluorescent membrane dyes PKH2 and PKH26 have been unknown, although their use in cell tracking experiments has increased dramatically. To eliminate the phototoxicity-induced alteration in cell function and morphology, it is essential to examine the suspicious phototoxicity of these dyes.

METHODS

Chemical and phototoxic effects of PKH dyes on the human hematopoietic KG1a cell line were examined. To minimize phototoxicity in long-term cell tracking experiments lasting up to 18 h with a fluorescence microscope system, time-lapse monitoring with different time intervals and exposure times was introduced.

RESULTS

There were no significant effects of the two PKH dyes on cell viability and growth when using dye concentrations up to 5 microM. However, when stained cells were exposed to excitation light, cell viability decreased dramatically, showing the phototoxicity of the PKH dyes. More than 60% of cells stained with 5 microM PKH26 died after 5 min of continuous light exposure. The phototoxic effect was more extensive in cells stained with higher concentrations of the dyes.

CONCLUSIONS

We present guidelines for the optimal use of these dyes by using a defined hardware configuration.

A flow cytometric method to assess antigen-specific proliferative responses of different subpopulations of fresh and cryopreserved human peripheral blood mononuclear cells

We have used PKH26 dye, which is incorporated stably into the membrane of cells, to determine, using flow cytometry, lymphocyte proliferative responses to the antigen tetanus toxoid in fresh and cryopreserved samples. Measuring cell proliferation with this dye has advantages over either 3H-thymidine or Bromodeoxyuridine (BrdU). Whereas the existing methods measure proliferation at a single time point, PKH26 gives a cumulative measure of cell proliferation. As PKH26 is incorporated into the cell membrane, cells do not have to be permeabilised to allow dye incorporation into a cytoplasmic compartment. Most importantly, PKH26 can be used in combination with monoclonal antibodies to surface markers on mixed populations of cells, to determine the proliferation of individual subpopulations, without the need for prior cell fractionation. We also show that PKH26 can be used with similar efficacy in both fresh and cryopreserved samples. In addition since PKH26 is a cumulative measure of proliferative responses we were able to show that restimulation of the dividing population in vitro with fresh antigen presenting cells (APC) and antigen permits characterisation of a further proliferating cell population. The use of PKH26 dye in combination with cell phenotyping and measurement of cytokine production at the single cell level will prove a powerful tool for multiparameter analyses of cellular responses to antigen.

Expression of Constitutively Activated Human c-Kit in Myb Transformed Early Myeloid Cells Leads to Factor Independence, Histiocytic Differentiation, and Tumorigenicity

The cDNAs encoding wild type (WT) human receptor tyrosine kinase c-Kit and a constitutively activated mutant, V816Kit, were introduced into granulocyte-macrophage colony-stimulating factor (GM-CSF )-dependent early murine hemopoietic cells, which had been transformed with activated Myb. WTKit cells were able to grow in the presence of the human ligand for Kit, stem cell factor (SCF ), but displayed reduced growth and clonogenic potential in either SCF or GM-CSF compared with the parental cells in GM-CSF. In contrast, V816Kit cells grew without factor at a higher rate than the parental cells in GM-CSF and displayed increased clonogenicity. Dissection of the growth characteristics in liquid culture showed that in the presence of appropriate factors, the different populations had similar proliferation rates, but that V816Kit profoundly increased cell survival compared with WTKit or parental cells. This suggests that the signals transduced by WTKit activated with SCF, and by V816Kit, were not identical. Also, WTKit and V816Kit-expressing cells both varied from the early myeloid progenitor phenotype of the parental cells and gave rise to a small number of large to giant adherent cells that expressed macrophage (α-naphthyl acetate) esterase and neutrophil (naphtol-AS-D-chloroacetate) esterase, were highly phagocytic and phenotypically resembled histiocytes. Thus, WTKit activated by SCF and V816Kit were able to induce differentiation in a proportion of Myb-transformed myeloid cells. The factor independent V816Kit cells, unlike the parental and WTKit expressing cells, were shown to produce tumors of highly mitotic, invasive cells at various stages of differentiation in syngeneic mice. These results imply that constitutively activated Kit can promote the development of differentiated myeloid tumors and that its oncogenic effects are not restricted to lineages (mast cell and B-cell acute lymphoblastic leukemia), which have been reported previously. Furthermore, the mixed populations of cells in culture and in the tumors phenotypically resembled the leukemic cells from patients with monocytic leukemia with histiocytic differentiation (acute myeloid leukemia-M5c), a newly proposed subtype of myeloid leukemia.

Expression of Constitutively Activated Human c-Kit in Myb Transformed Early Myeloid Cells Leads to Factor Independence, Histiocytic Differentiation, and Tumorigenicity

The cDNAs encoding wild type (WT) human receptor tyrosine kinase c-Kit and a constitutively activated mutant, V816Kit, were introduced into granulocyte-macrophage colony-stimulating factor (GM-CSF )-dependent early murine hemopoietic cells, which had been transformed with activated Myb. WTKit cells were able to grow in the presence of the human ligand for Kit, stem cell factor (SCF ), but displayed reduced growth and clonogenic potential in either SCF or GM-CSF compared with the parental cells in GM-CSF. In contrast, V816Kit cells grew without factor at a higher rate than the parental cells in GM-CSF and displayed increased clonogenicity. Dissection of the growth characteristics in liquid culture showed that in the presence of appropriate factors, the different populations had similar proliferation rates, but that V816Kit profoundly increased cell survival compared with WTKit or parental cells. This suggests that the signals transduced by WTKit activated with SCF, and by V816Kit, were not identical. Also, WTKit and V816Kit-expressing cells both varied from the early myeloid progenitor phenotype of the parental cells and gave rise to a small number of large to giant adherent cells that expressed macrophage (α-naphthyl acetate) esterase and neutrophil (naphtol-AS-D-chloroacetate) esterase, were highly phagocytic and phenotypically resembled histiocytes. Thus, WTKit activated by SCF and V816Kit were able to induce differentiation in a proportion of Myb-transformed myeloid cells. The factor independent V816Kit cells, unlike the parental and WTKit expressing cells, were shown to produce tumors of highly mitotic, invasive cells at various stages of differentiation in syngeneic mice. These results imply that constitutively activated Kit can promote the development of differentiated myeloid tumors and that its oncogenic effects are not restricted to lineages (mast cell and B-cell acute lymphoblastic leukemia), which have been reported previously. Furthermore, the mixed populations of cells in culture and in the tumors phenotypically resembled the leukemic cells from patients with monocytic leukemia with histiocytic differentiation (acute myeloid leukemia-M5c), a newly proposed subtype of myeloid leukemia.

Interaction of acute leukemia cells with the bone marrow microenvironment: implications for control of minimal residual disease

There is increasing evidence for an interaction between acute leukemia cells and the microenvironment of the bone marrow. Blast cells from cases of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) bind to cellular and extracellular matrix components of the bone marrow stroma. In AML, adhesion to stroma is mediated by the combined action of beta 1 (principally VLA-4) and beta 2 integrins, while in precursor-B ALL VLA-4 and VLA-5 integrins play a major role. Adhesion molecules such as CD31, CD44, non-beta 1, beta 2 integrins, growth factor receptors such as c-kit, and other molecules are also likely to play a role. Binding of acute leukemia blasts to ligands on stroma has several pathophysiological consequences. Stromal contact is able to inhibit programmed cell death (apoptosis) in a proportion of cases of both AML and ALL. In ALL, diffusible molecules derived from stroma appear to contribute. Marrow stroma also plays a part in regulating leukemic cell proliferation. While this is partly due to stromal production of hemopoietic growth factors, in soluble or transmembrane form or bound to extracellular matrix, signalling mediated directly by binding of adhesion molecules on leukemic cells may also have a role. Contact of ALL blasts with marrow fibroblasts is followed by migration of leukemic cells, utilizing VLA-4 and VLA-5 integrins, potentially allowing homing of blasts to favourable microenvironmental sites, or controlling egress into the circulation. AML cells compete for stromal binding sites with natural killer cells and cytotoxic lymphocytes, which are known to inhibit their clonogenic growth. We speculate that these complex interactions between leukemic blasts, cellular and matrix components of stroma, and cytotoxic lymphocytes, play a critical role in determining the fate of small numbers of leukemic cells surviving after cytotoxic chemotherapy.

Viable bone marrow stromal cells are required for the in vitro survival of B-cell precursor acute lymphoblastic leukemic cells

The growth of B-cell precursor acute lymphoblastic leukemic (BCP ALL) cells in vitro is dependent on interactions with bone marrow (BM) stromal cells. We have recently demonstrated that the rate of cell division of BCP ALL cells increases when cultured in direct contact with BM stromal cells. A number of studies have examined the binding of BCP ALL cells to BM stromal cells and extracellular matrix components. To date there have been no studies examining the effect of such binding on the growth and survival of BCP ALL cells. In this study, by measuring the growth parameters of these cells with use of a lipophilic fluorescent probe, PKH 26 GL, we demonstrate the positive effect of viable BM stromal cells on BCP ALL cell survival in 10 patient samples. At the same time, by comparing these cultures with cultures of the same patient samples in the presence of glutaraldehyde-fixed stromal cells, deoxycholic acid-derived stromal cell matrices, purified laminin, collagen or fibronectin, the role of various stromal cell-derived contact components in BCP ALL survival was tested. It was shown that the survival of BCP ALL cells in vitro was dependent upon viable BM stromal cells present in co-culture as the various contact components did not show any functional effect on BCP ALL cell survival.

Human bone marrow stromal cell contact and soluble factors have different effects on the survival and proliferation of paediatric B-lineage acute lymphoblastic leukaemic blasts

Recent studies have confirmed that in vitro viability and proliferation of precursor B-cell leukaemia (ALL) cells are linked to the presence of bone marrow derived stromal cells. To investigate whether this effect is mediated by direct contact or through the action of soluble factors, using a method we have recently described, the growth parameters of ALL bone marrow blast cells from eight newly diagnosed patients were determined with the lipophilic fluorescent probe PKH 26 GL. The viability of ALL cells and the rate of cell division in cultures containing either medium alone; stromal cell conditioned medium; stromal cell layers allowing direct contact, or in 0.4 microns microporous membrane cultures suspended above stromal cell layers were examined. In all eight samples an improved maintenance of ALL cells in a viable state in cultures containing bone marrow stromal cells was observed. The survival of leukaemic cells was equivalent in 0.4 microns microporous membrane cultures suspended above stromal cell layers and in cultures of leukaemic cells in direct contact with stromal cell layers. It was thus demonstrated that this effect was mediated by the action of soluble factor(s) present in these cultures. However, the improved maintenance of ALL cells in a viable state was observed in only one of the eight cases when ALL cells were cultured in stromal cell conditioned medium alone. The highest rate of cell division of leukaemic cells was observed in ALL cells in direct contact with bone marrow stromal cells. The activities of stromal cell derived soluble factors could not be reproduced by recombinant forms of likely candidate factors including IL-1 beta, IL-4, IL-6, IL-7, SCF, TNF alpha, TGF beta, LIF, NGF or a mixture of these factors when examined in cultures of the same patient samples. This study implicates the existence of a novel bone marrow derived factor(s) that improves survival of ALL cells in vitro.