Flow cytometric sorting of paraffin-embedded tumor tissues considerably improves molecular genetic analysis

The characterization of genetic aberrations in paraffin-embedded tumor material is impaired by contaminating normal cells. In the present study on the genetic causes of loss of HLA expression in diffuse large B-cell lymphoma (DLBCL), we compared the efficacy of microdissection with flow cytometric sorting of tumor cells. Single-cell suspensions from paraffin-embedded material of 5 DLBCL cases were stained for CD79a and DNA content (propidium iodide). Fluorescent in situ hybridization (FISH) using HLA class II and chromosome 6 centromeric probes and loss of heterozygosity (LOH) analysis with 5 HLA-specific microsatellite markers were performed on microdissected and flow cytometry-sorted fractions. FISH confirmed considerable enrichment of the samples after flow cytometric sorting and disclosed tumor heterogeneity in 4 cases. Moreover, lymphomas with a so-called zebra LOH pattern in the microdissected material showed unambiguous LOH after flow cytometric sorting, revealing in 1 case a biologically relevant hemizygous deletion in the HLA region.

The interaction of human dendritic cells with yeast and germ-tube forms ofCandida albicansleads to efficient fungal processing, dendritic cell maturation, and acquisition of a Th1 response-promoting function

T helper cell type 1 (Th1) cell-mediated immunity plays a critical role in protection against the opportunistic pathogen Candida albicans. Virulence of the fungus is closely associated with its ability to form germ-tubes (GT), the early phase of the dimorphic transition from the commensal yeast (Y) to the more invasive hyphal (H) form. In this study, we examined the functional outcome of the interaction of Y or GT forms with human dendritic cells (DCs), professional antigen-presenting cells, which are pivotal for initiation and modulation of T cell responses. DCs phagocytosed and killed Y and GT cells with a comparable efficiency, becoming able to trigger strong proliferative responses by Candida-specific, autologous T cell clones. Both fungal forms induced DC maturation, as indicated by up-regulation of CD83, CD80, CD86, CD40, and major histocompatibility complex classes I and II surface antigens. Chemokine receptors were also modulated in Candida-DCs, which showed increased CCR7/CXCR4 and decreased CCR5 expression. Y- and GT-activated DCs differed in the pattern of cytokine expression. In particular, GT cells, in common with fully differentiated H cells, induced significantly more elevated levels of interleukin (IL)-10 than Y cells. Nevertheless, Y-, GT-, or H-pulsed DCs secreted comparable amounts of IL-12p70. In addition, irrespective of the fungal form triggering DC activation, Candida-DCs acquired the ability to prime naive T lymphocytes with a defined Th1 phenotype. Overall, our findings highlight the induction of substantially similar functional patterns in human DCs encountering the different forms of growth of C. albicans, both seemingly activating the Th1-type immunity which is characteristic of the healthy human subjects, naturally immunized and protected against the fungus.

Quantification and characterization of specific T-cells by antigen-specific cytokine production using ELISPOT assay or intracellular cytokine staining

The novel generation of sensitive T-cell assays facilitates the direct quantitation and characterization of specific T-cell responses. Functional T-cell assays such as the ELISPOT assay and the intracellular cytokine cytometry (ICC) employ the antigen-specific induction of cytokines to detect specific T-cells on a single cell level. ICC has the advantage that the simultaneous phenotypic characterization of the antigen-specific T-cells is possible. There is evidence now from clinical cancer vaccination trials, that there is a relationship between the detection of vaccine-induced T-cells by cytokine-based assays and clinical responses. As these assays become increasingly relevant in clinical practice to suggest issues of assay validation and quality control become of major importance.

[Immunophenotyping of 106 adult patients with acute leukemia by flow cytometry]

OBJECTIVE

To study the immunophenotyping of adult patients with acute leukemia and its association with the prognosis.

METHODS

Immunophenotyping was performed in 106 adult patients with acute leukemia by three-color flow cytometry analysis using CD34/SSC gating.

RESULTS

The antigens expressed in 71 patients with acute myeloid leukemia (AML) were mainly CD13, CD33, HLA-DR, CD34 and CD117. Lymphoid antigen expression was identified in 23.9% adult AML patients and CD56 antigen expression in 15.5% of the AML patients. In 29 patients with acute lymphoblastic leukemia (ALL), the expressed antigens were mainly HLA-DR, CD10, CD19, CD34 and CD7, and 34.5% of these patients were found to be positive for myeloid antigen expression. Complete remission (CR) rate in AML patients with lymphoid antigen expression after chemotherapy was lower than that in AML patients without lymphoid antigen expression (52.9% vs 77.8%, P<0.05), and no significant impact was noted of myeloid antigen expression in ALL on the CR of the patients (70.0% vs 94.7%, P>0.05). The CR rate in AML with CD56 antigen expression was lower than that in AML without CD56 expression (36.4% vs 78.3%, P<0.025), and the CR rate in CD34+ AML was lower than that in CD34- AML (56.0% vs 80.4%, P<0.05).

CONCLUSIONS

Gating of CD45/SSC can eliminate the interference of normal cells to render more reliable immunophenotyping results. The expressions of CD56+, CD34+, lymphoid antigen in adult AML patients, who have lower CR rate, often signify poor prognosis.

Dendritic cell subsets in blood and lymphoid tissue of rhesus monkeys and their mobilization with Flt3 ligand

We provide phenotypic and functional evidence of premonocytoid dendritic cells (DCs) and preplasmacytoid DCs in blood and of corresponding DC subsets in secondary lymphoid tissue of rhesus monkeys. Subsets were identified and sorted by 4-color flow cytometry using antihuman monoclonal antibodies cross-reactive with rhesus monkey. To mobilize pre-DC subsets, fms-like tyrosine 3 kinase ligand (Flt3L; 100 microg/kg subcutaneously) was administered for 10 days. Presumptive pre-DC subsets were identified within the lineage- (Lin-) major histocompatibility complex (MHC) class II+ fraction of blood mononuclear cells. Premonocytoid DCs were CD11c+CD123- (interleukin-3Ralpha- [IL-3Ralpha-]). Preplasmacytoid DCs were characterized as CD11c-CD123++ Flt3L increased the CD11c+ pre-DC (7-fold) and CD123++ pre-DC subsets (3-fold) in blood. The freshly isolated CD11c+ pre-DC subset induced modest proliferation of naive allogeneic T cells. After overnight culture with granulocyte macro-phage-colony-stimulating factor (GMCSF) and CD40L, both subsets up-regulated surface costimulatory molecules, and CD11c+ pre-DCs became potent allostimulators. Freshly isolated CD123++ pre-DCs showed typical plasmacytoid morphology and, when cultured with IL-3 and CD40L for 72 hours, developed mature DC morphology. Following stimulation with CD40L, CD11c+ pre-DCs secreted increased levels of IL-12p40. Importantly, herpes simplex virus-stimulated CD123++ pre-DCs, but not CD11c+ pre-DCs, secreted interferon-alpha (IFN-alpha). Corresponding DC subsets were identified by flow analysis and immunohistochemistry in lymph nodes wherein both populations were increased 2- to 3-fold by Flt3L administration. CD123+ pre-DCs produced IFN-alpha in response to in vivo viral infection. Thus, rhesus monkeys exhibit 2 distinct DC precursor populations that closely resemble those of humans. Both are mobilized into blood and lymphoid tissue by Flt3L, offering potential for their further characterization and possible therapeutic application.

Isolation of Rare Isotype Switch Variants in Hybridoma Cell Lines Using an Agarose Gel Microdrop-Based Protein Secretion Assay

Using gel microdrop (GMD) encapsulation technology and fluorescence-activated cell storing (FACS), we have developed a rapid, sensitive, and reliable method for discriminating and recovering rare isotypic switch variants in hybridoma cell lines. Using the GMD-based IgSwitch assay, a novel approach for isolating subpopulations of IgG-secreting hybridoma cells present at a frequency of approximately 1-10 in 10(6), we successfully isolated spontaneous and in vitro-induced isotypic switch variants in less than half the time required for conventional sublining. The effectiveness and specificity of the assay are demonstrated.

The origin and identification of unknown events associated with low-level leucocyte counting by flow cytometry

BACKGROUND AND OBJECTIVES

Flow cytometric enumeration of residual leucocytes (WBC) in leucocyte-depleted components occasionally reveals a population of events that stain with propidium iodide, but which are outside the main counting region. These extraregional events may result in discrepancies in residual WBC counts.

MATERIALS AND METHODS

To identify the origin of these unknown events, separate populations of mononuclear cells and polymorphonuclear neutrophils (PMNs) (prepared by density-gradient centrifugation) were spiked into leucocyte-depleted red cell concentrates (RCC) to a concentration of 150 cells/ microl and assessed, using LeucoCount and DNA Prep reagents, by flow cytometry. In addition, isolated WBC nuclei, DNA in saline, or enzymatically digested free DNA, was spiked into diluted whole blood (final concentration 5 microg/ml).

RESULTS

Isolated WBC nuclei fell in the main counting region of the dot plot. Extraregional events were generated in leucocyte-depleted RCC spiked with PMN (17/ microl by day 4), but not with mononuclear cells, and increased with sample storage (4 days). A significantly (P < 0.01) greater number of extraregional events was observed using the LeucoCount reagent, compared with the DNA Prep reagent. Enzymatically digested WBC nuclei or free DNA, added to diluted whole blood, generated extraregional events using LeucoCount, but not the DNA Prep reagent. When free DNA was enzymatically digested, no extraregional events were observed.

CONCLUSIONS

These previously unidentified events are probably fragmented nuclei or free DNA originating from PMN owing to a combination of ageing and reagent addition. Currently, in our protocols, the region used for WBC enumeration counts intact WBC nuclei. To achieve WBC counting consistency, flow cytometric gating protocols must be standardized, and a decision taken as to whether to include extraregional events in the count.

Measuring T cell-mediated cytotoxicity using fluorogenic caspase substrates

Cytotoxic T lymphocytes (CTLs) play a major role in the immune response against viruses and other intracellular pathogens. In addition, CTLs are implicated in the control of tumor cells in certain settings. Accurate measures of CTL function are of critical importance to study the pathogenesis of infectious diseases and to evaluate the efficacy of new vaccines and immunotherapies. To this end, we have recently developed a flow cytometry-based CTL (FCC) assay that measures the CTL-induced caspase activation within target cells using cell permeable fluorogenic caspase substrates. This novel assay reliably detects, by flow cytometry or fluorescence/confocal microscopy, antigen-specific CTLs in a wide variety of human and murine systems, and is safer and more informative than the standard 51Cr-release assay. In addition, the flow cytometric CTL (FCC) assay provides an alternative method that is often more sensitive and physiologically informative when compared to previously described FCC assays, as it measures a biological indicator of apoptosis within the target cell. The FCC assay may thus represent a useful tool to further understand the molecular and cellular mechanisms that underlie CTL-mediated killing during tumorigenesis or following infection with viruses or other intracellular pathogens.

Sensitive and viable identification of antigen-specific CD8+ T cells by a flow cytometric assay for degranulation

Flow cytometric detection of antigen-specific CD8+ T cells has previously been limited to MHC-class I tetramer staining or intracellular cytokine production, neither of which measure the cytolytic potential of these cells. Here we present a novel technique to enumerate antigen-specific CD8+ T cells using a marker expressed on the cell surface following activation induced degranulation, a necessary precursor of cytolysis. This assay measures the exposure of CD107a and b, present in the membrane of cytotoxic granules, onto the cell surface as a result of degranulation. Acquisition of cell surface CD107a and b is associated with loss of intracellular perforin and is inhibited by colchicine, indicating that exposure of CD107a and b to the cell surface is dependent on degranulation. CD107a and b are expressed on the cell surface of CD8+ T cells following activation with cognate peptide, concordant with production of intracellular IFNgamma. Finally, CD107-expressing CD8+ T cells are shown to mediate cytolytic activity in an antigen-specific manner. Measurement of CD107a and b expression can also be combined with MHC-class I tetramer labeling and intracellular cytokine staining to provide a more complete assessment of the functionality of CD8+T cells expressing cognate T cell receptors (TCR).

The flow cytometric PKH-26 assay for the determination of T-cell mediated cytotoxic activity

We present a rapid flow cytometric and non-radioactive functional assay developed for the determination of the cytotoxic activity of T lymphocytes, natural killer cells, and lymphokine-activated killer cells. In contrast to indirect evaluation of cytotoxicity using radioactive assays, this assay is based on the quantitative and qualitative flow cytometric analysis of cell damage on a single cell level. Target cells are stained with PKH-26, a lipophilic dye that stably integrates into the cell membrane, without disturbing its surface marker expression. It, thus, permits the distinction between target and effector cells. After short term in vitro incubation (1.5-3h), AnnexinV-FITC (ann-FITC) staining allows to discriminate between apoptotic and non-apoptotic target cells. Data analysis is performed first by gating on PKH-26 positive target cells, followed by the analysis of the ann-FITC positive subpopulation. The percentage of cytotoxicity in the PKH-26 gated cell population is calculated by subtracting unspecific ann-FITC positive target cells, measured in appropriate controls without effector cells. Using in vitro generated antigen-specific cytotoxic T lymphocytes, we demonstrate that this flow cytometric assay is sensitive, correlates well with the standard 51Cr release assay, and is easy to handle.

Development and use of a vaccinia virus neutralization assay based on flow cytometric detection of green fluorescent protein

A rapid and sensitive neutralization assay is required to evaluate alternative smallpox vaccines. Here we describe the development and use of a 96-well plate, semi-automated, flow cytometric assay that uses a recombinant vaccinia virus expressing enhanced green fluorescent protein and which would be applicable to other viruses.

Effects of endogenous and synthetic opioid peptides on neutrophil function in vitro

BACKGROUND

Opioid peptides released from immunocytes during inflammation and stress in critically ill patients are associated with an altered immune response. Moreover, concentrations of opioid peptides are increased in peripheral blood and at the sites of inflammatory reactions.

METHODS

Using flow cytometric assay of whole human blood, we investigated direct effects of endogenous and synthetic opioid peptides on surface expression of complement receptors CD35 and CD11b/CD18 and Fcã receptor III CD16, and superoxide anion generation of neutrophils.

RESULTS

The endogenous opioid peptides beta-endorphin(1-31) and met-enkephalin, representing the N-terminal fragment of beta-endorphin(1-31), and the synthetic delta opioid receptor agonists D-Ala(2)-D-Leu(5)-enkephalin and D-Pen(2)-enkephalin produced concentration-dependent stimulation of neutrophil activity. Incubation with met-enkephalin 10(-7) M or beta-endorphin(1-31) 10(-7) M led to an increase in receptor expression of up to 10% (met-enkephalin) and 15% (beta-endorphin(1-31)). After incubation with D-Ala(2)-D-Leu(5)-enkephalin or D-Pen(2/5)-enkephalin, receptor expression was increased by up to 30%. This correlated with concentration-dependent stimulation of the production of reactive oxygen intermediates, as shown by an increase of up to 40% in oxidative burst activity. All effects were abolished after preincubation with naloxone or with the selective delta opioid antagonist naltrindole, whereas the selective micro receptor antagonist d-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH(2) showed only partial inhibitory effects.

CONCLUSIONS

Our data suggest a delta opioid receptor-mediated stimulatory effect on neutrophil function. beta-Endorphin(27-31), the C-terminal fragment of beta-endorphin(1-31), did not alter neutrophil function, indicating that beta-endorphin(1-31) mediates its effect on neutrophils via the N-terminal fragment. This study may contribute to a better understanding of neuroimmune interaction.

Increased cell apoptosis in bone marrow trephine biopsies and immunomagnetically isolated myeloid progenitor cells in patients with chronic idiopathic neutropenia

The frequency of apoptotic cells in bone marrow trephine biopsies and cytospins of immunomagnetically isolated myeloid progenitor cells was determined in 39 patients with chronic idiopathic neutropenia (CIN) and 12 hematologically normal individuals using the in situ end-labeling (ISEL) apoptosis detection method. We found that 66.7% of the patients but none of the normal controls displayed apoptotic cells equal to or higher than 5% of the total mononuclear cells in bone marrow biopsies (p<0.01). In the double stain, we also found that the proportion of apoptotic CD15(+) myeloid precursor cells did not differ significantly between patients and control subjects, while the proportion of apoptotic CD34(+) hemopoietic cells could not be estimated with accuracy because of the presence of CD34(+) endothelial cells. Significantly increased apoptosis was noted in cytospins of immunomagnetically isolated patient CD34(+) and CD34(+)/CD33(+) cells but not CD34(-)/CD33(+) cells, compared to the controls ( p<0.001, p<0.02 and p>0.05, respectively). These findings confirm and extend our previous observations in flow-cytometric studies of apoptosis in CIN, indicating that increased apoptosis in CIN bone marrow concerns mainly the CD34(+) and CD34(+)/CD33(+) progenitor cell compartments. We conclude that the accelerated apoptosis in these compartments may account for the impaired neutrophil production in CIN patients.

[Detection of platelet activation by flow cytometry in patients with pre-eclampsia]

OBJECTIVE

To explore the clinical significance of expression alterations of static and activated platelet glycoprotein CD41a, CD62p, and CD63 in patients with pre-eclampsia.

METHODS

We used non-washing immunolabeling technique for fluorescence labeling of the static and activated platelet with CD41a, CD62p, and CD63 monoclonal antibodies of the blood samples from 16 patients with pre-eclampsia, 15 women with normal pregnancies and 20 healthy subjects. The expression of the monoclonal antibody was detected by flow cytometry.

RESULTS

The average static and activated platelet glycoprotein CD41a, CD62p, and CD63 expression levels in patients with pre-eclampsia were apparently higher than those of the normal pregnant women (P<0.01), while the comparison between the latter and the control group did not reveal any significant differences (P>0.05).

CONCLUSION

High levels of platelet glycoprotein CD62p and CD63 expressions are present in patients with preeclampsia, suggesting the presence of platelet activation in these patients.

Normal Features of Tissue-Engineered Auricular Cartilage by Flow Cytometry and Histology: Patient Safety

BACKGROUND: Cytokinetic abnormalities in DNA content, such as aneuploidy, haploidy, and tetraploidy, have been found to occur in human cartilaginous tumors. The high number of chondrocytes needed for tissue-engineered cartilaginous implants requires the cells to be passaged repeatedly. The theoretical risk of changes in the normal diploid state of these cells during their growth in vitro and after generation of tissue-engineered cartilage in vivo is not known.

MATERIALS AND METHODS: Auricular chondrocytes were obtained from 6 patients and cultured in vitro. Chondrocyte number was increased by repeated passaging. The passaged cells were implanted in nude mice for 8 weeks to generate tissue-engineered cartilage. Fresh control chondrocytes along with the passaged cells and cells obtained from the tissue-engineered constructs were collected and compared for DNA content by flow cytometry.

RESULTS: Flow cytometry demonstrated 100% diploidy with no evidence of aneuploidy, haploidy, or tetraploidy in all groups of cells. Histology of the tissue-engineered cartilage also showed no evidence of cellular atypia.

CONCLUSION: The number of human auricular chondrocytes can be increased by repeated passaging and passaged chondrocytes can be safely used for implantation to generate tissue-engineered constructs without a change in the normal diploid state of the cells. Histology of the cartilage generated showed normal features without atypia. (Otolaryngol Head Neck Surg 2003;129:390–6.)

A protocol for combining proliferation, tetramer staining and intracellular cytokine detection for the flow-cytometric analysis of antigen specific T-cells

Flow-cytometry can be used in different ways in order to analyze or enumerate antigen specific T-cells. The three basic principles are direct staining of the T-cell receptor using so called tetramer reagents, staining intracellular cytokines following antigen-specific ex vivo T-cell activation or staining with dyes that are incorporated (increase in staining) or distributed between daughter cells (decrease in staining) upon proliferation in response to a specific antigen challenge. Each system has its advantages and disadvantages. Here we demonstrate that tetramer staining, cytokine flow cytometry and staining with CFDA-SE can be combined permitting the analysis of proliferation and cytokine production with a subset of T-cells specific for a single peptide antigen.

Isolation of mast cell secretory lysosomes using flow cytometry

BACKGROUND

Mast cells are specialized secretory cells of the immune system. Through exocytosis of their secretory lysosomes and secretory granules, mast cells release biologically active substances such as histamine and proteases. Mast cell secretory granules have been studied extensively but much less attention has been given to secretory lysosomes. Studies on mast cell secretory lysosomes are limited by the lack of selective markers and the difficulty to isolate this organelle from conventional lysosomes. Our goal was to develop better tools to study secretory lysosomes.

METHODS

We engineered a rat mast cell line over expressing a rat mast cell protease (RMCP) tagged with a red fluorescent protein (RMCP-DsRed). We used single organelle flow analysis (SOFA) to detect fluorescently labeled secretory lysosomes. The labeled organelles were then sorted using the fluorescence-assisted organelle sorting (FAOS) method.

RESULTS

We show that the RMCP-DsRed fusion protein selectively localizes to the lysosomal compartment and is exocytosed upon activation, confirming its localization in secretory lysosomes. Lysosomal fractions from cells expressing the RMCP-DsRed fusion were analyzed by SOFA and a specific population of secretory lysosome was identified. Finally, we sorted secretory lysosomes and showed that the sorted material had a higher specific activity for the compartment marker hexosaminidase than a sample obtained by conventional methods.

CONCLUSIONS

Our work further demonstrates the usefulness of flow cytometry to study cellular organelles, and provides new tools to better understand the physiology of secretory lysosomes.

Absolute TCD4+ counting by a minimalist dual-platform flow cytometric method

The aim of this work was to compare the performance of an absolute TCD4+ counting method based on total WBC gating versus the standard lymphocyte (Ly) gating method, in order to develop a flow cytometric (FCM) minimalist strategy for TCD4+ enumeration.

METHOD

132 routine peripheral blood samples, mainly from HIV infected patients, were labelled with CD3-FITC/CD4-PE/CD45-PECy5 and analyzed by two gating methods: a) standard method based on Ly immunological gating (CD45++SSClow), followed by the determination of CD3+CD4+ percentage and absolute number (# calculation using Ly # from hematological analyser (HA); b) total WBC immunological gate on biparametric scatter CD45/CD4, followed by CD4++SSClow percentage determination and absolute number calculation using WBC absolute number from hematological counter without using the WBC differential. Moreover on 63 samples Ly # based on Ly % from FCM and WBC counting from HA was compared with Ly # from HA.

RESULTS

The TCD4+/microL ranged from 3 to 3277 and the statistical analysis results showed: a) linear regression: r2 = 0.9847; b) Bland & Altman analysis: difference mean = -56.22; agreement range = +95.68 / -208.12; c) the mean of result difference/mean value*100 between two methods was -9.06%; d) comparison between regression line and the boundaries for acceptable residual values based on regressed confidence limits found by A. Kunkl et al showed regression line within boundaries near the upper limits. The Ly/microL count ranged from 635 to 8752. The statistical analysis results showed: a) linear regression: r2 = 0.9764; b) Bland & Altman analysis: difference mean = -362.93; agreement range = +134.51 / -860.37; c) the mean of result difference/mean value*100 between two methods was -16.12%.

CONCLUSIONS

Our results suggest a fair agreement between the two gating methods, but the one based on total WBC gate gives TCD4+/microL counts systematically higher than the standard method. This finding can be attributed to a systematic lower estimation of Ly% by HA.

Measurements and modeling of water transport and osmoregulation in a single kidney cell using optical tweezers and videomicroscopy

With an optical tweezer installed in our optical microscope we grab a single Madin Darby Canine kidney cell and keep it suspended in the medium without touching the glass substrate or other cells. Since the optically trapped cell remains with a closely round shape, we can directly measure its volume by using videomicroscopy with digital image analysis. We submit this cell to a hyperosmotic shock (up-shock) and video record the process: the cell initially shrinks due to osmotic efflux of water and after a while, due to regulatory volume increase (RVI), an osmoregulation response, it inflates again (water influx) until it reaches a new volume (the regulatory volume VR). In addition to considering standard osmotic water transport, we model RVI using a simple phenomenological model. We obtain an expression for cell volume variation as a function of time that fits very well with our experimental data, where two characteristic times appear naturally: one related to water transport and the other related to RVI. From the fit we obtain water permeability, osmolyte influx rate for RVI, and regulatory volume. With the addition of the hormone vasopressin, water permeability increases while the regulatory volume decreases until inhibition of RVI. In summary, we present a technique to measure directly volume changes of a single isolated kidney cell under osmotic shock and a phenomenological analysis of water transport that takes into account osmoregulation.

[Large-scale real-time titration of green-fluorescence-protein-marked recombinant retrovirus: comparison with standard titration method]

OBJECTIVE

To compare large-scale real-time titration method (LaSRT) with standard titration method by flow cytometry (FACS) for determining the titers of green-fluorescence-protein (GFP)-marked recombinant retrovirus.

METHODS

(1) Standard titration method: NIH3T3 cells were inoculated at 2x10(5) /well in 6-well plate, and after cell culture for 12 h, 0.5 ml, 50 microl and 5 microl GFP-marked recombinant retrovirus (n=3) were respectively used to infect the cells, with the final concentration of polybrene being 8 microg/ml. Forty-eight hours later, the cells were treated with trypsin and assayed for the positive rate of GFP by means of FACS. When the positive rate was lower than 10%, the titer was calculated according to the equation: virus titer (TU/ml) =2x10(5)xGFP positive rate/volume of virus stock solution used. (2) LaSRT method: The cells were inoculated at 5,000 cells/well in a 96-well plate, and after cell culture for 12 h, 90 microl/well complete culture medium was used with 8 microg/ml polybrene and 10% newborn bovine serum, 10 microl virus was added into the first well, and ten-fold dilution of the previous virus-containing solution was performed before the virus was added into the next well (8 wells in each group, altogether 3 groups). Forty-eight hours later, inverted fluorescence microscope was used to observe the fluorescence-positive cells in each well. The virus titer was calculated according to the equation: virus titer (TU/ml) =mx10(n+1), where n is the serial number of the reference well, and m the number of positive cells. (3) LaSRT was used to study the influence of freezing/thawing on the titers of recombinant retroviruses.

RESULTS

The virus titer obtained with standard method by FACS was (1.54+/-0.38)x10(6) TU/ml, and that of LaSRT was (1.33+/-0.57)x10(6) TU/ml (P>0.05). After one cycle of freezing/thawing, the virus titer dropped to (18.1+/-9.9)% (n=7).

CONCLUSION

LaSRT is more rapid and convenient as well as easier to determine the virus titer compared with standard method, and no significant difference is found between the two titration methods.

Differences between peripheral blood and cord blood in the kinetics of lineage-restricted hematopoietic cells: implications for delayed platelet recovery following cord blood transplantation

Cord blood (CB) cells are a useful source of hematopoietic cells for transplantation. The hematopoietic activities of CB cells are different from those of bone marrow and peripheral blood (PB) cells. Platelet recovery is significantly slower after transplantation with CB cells than with cells from other sources. However, the cellular mechanisms underlying these differences have not been elucidated. We compared the surface marker expression profiles of PB and CB hematopoietic cells. We focused on two surface markers of hematopoietic cell immaturity, i.e., CD34 and AC133. In addition to differences in surface marker expression, the PB and CB cells showed nonidentical differentiation pathways from AC133(+)CD34(+) (immature) hematopoietic cells to terminally differentiated cells. The majority of the AC133(+)CD34(+) PB cells initially lost AC133 expression and eventually became AC133(-)CD34(-) cells. In contrast, the AC133(+)CD34(+) CB cells did not go through the intermediate AC133(-)CD34(+) stage and lost both markers simultaneously. Meanwhile, the vast majority of megakaryocyte progenitors were of the AC133(-)CD34(+) phenotype. We conclude that the delayed recovery of platelets after CB transplantation is due to both subpopulation distribution and the process of differentiation from AC133(+)CD34(+) cells.

Colocalization analysis of sialomucins CD34 and CD164

Flow cytometric protocols are employed to identify and characterize hemopoietic stem/progenitor populations before transplantation. Cell surface antigens, including CD34, are employed in this process and widely used in harvest protocols, which largely ignores the potential functional role of such antigens. Transmembrane glycoprotein sialomucins, including CD34 and CD164, have been implicated in cell-to-cell interactions and activation. CD164, also expressed on early hemopoietic populations, was reported to have a possible function facilitating CD34(+) cells to adhere to bone marrow stroma. In this study, we employed high-definition laser-scanning confocal microscopy to investigate CD34 and CD164 surface co-localization patterns on bone marrow and cord blood cells and to compare the expression patterns using a three-dimensional computer-generated method developed in house. Differential interference microscopy analysis revealed bone marrow membrane activity was higher than the corresponding cord blood counterpart, perhaps indicating the marrow microenvironmental nature. Fluorescence analysis of CD34 and CD164 antigens showed both were expressed first in a halo-like pattern and second in antigen-dense pockets. Three-dimensional computer analyses further revealed that this pocketing corresponded to dense crest-like surface structures appearing to rise from the point of adherence on the slide. Further, it was found that CD34 and CD164 display strong colocalization patterns on cells expressing both antigens. The dual nature of the CD34 and CD164 antigens discovered here lends further evidence to the previous literature implicating a strong functional link between these two sialomucins, which should be considered in the transplantation arena and in the function of such sialomucins as negative regulators of cell proliferation.