Cytofluorometric methods for assessing absolute numbers of cell subsets in blood. European Working Group on Clinical Cell Analysis

Flow cytometric lymphocyte subset enumeration: 10 years of external quality assessment in the Benelux countries

A biannual external quality assessment (EQA) scheme for flow cytometric lymphocyte immunophenotyping is operational in the Benelux countries since 1996. We studied the effects of the methods used on assay outcome, and whether or not this EQA exercise was effective in reducing between-laboratory variation. Eighty test samples were distributed in 20 biannual send-outs. Per send-out, 50-71 participants were requested to enumerate CD3+, CD4+, and CD8+ T cells, B cells, and NK cells, and to provide methodological details. Participants received written debriefings with personalized recommendations after each send-out. For this report, data were analyzed using robust multivariate regression. Five variables were associated with significant positive or negative bias of absolute lymphocyte subset counts: (i) platform methodology (i.e., single-platform assays yielded lower CD4+ and CD8+ T-cell counts than did dual-platform assays); (ii) sample preparation technique (i.e., assays based on mononuclear cells isolation yielded lower T-cell counts than those based on red cell lysis); (iii) gating strategies based on CD45 and sideward scatter gating of lymphocytes yielded higher CD4+ T-cell counts than those based on "backgating" of lymphocytes guided by CD45 and CD14); (iv) stabilized samples were generally associated with higher lymphocyte subset counts than nonstabilized samples; and (v) laboratory. Platform methodology, sample stabilization, and laboratory also affected assay variability. With time, assay variability tended to decline; this trend was significant for B-cell counts only. In addition, significant bias and variability of results, independent of the variables tested for in this analysis, were also associated with individual laboratories. In spite of our recommendations, participants tended to standardize their techniques mainly with respect to sample preparation and gating strategies, but less with absolute counting techniques. Failure to fully standardize protocols may have led to only modest reductions in variability of results between laboratories.

Evaluation of a green laser pointer for flow cytometry

Flow cytometers typically incorporate expensive lasers with high-quality (TEM00) output beam structure and very stable output power, significantly increasing system cost and power requirements. Red diode lasers minimize power consumption and cost, but limit fluorophore selection. Low-cost DPSS laser pointer modules could possibly offer increased wavelength selection but presumed emission instability has limited their use. A $160 DPSS 532 nm laser pointer module was first evaluated for noise characteristics and then used as the excitation light source in a custom-built flow cytometer for the analysis of fluorescent calibration and alignment microspheres. Eight of ten modules tested were very quiet (RMS noise < or = 0.6% between 0 and 5 MHz). With a quiet laser pointer module as the light source in a slow-flow system, fluorescence measurements from alignment microspheres produced CVs of about 3.3%. Furthermore, the use of extended transit times and < or =1 mW of laser power produced both baseline resolution of all 8 peaks in a set of Rainbow microspheres, and a detection limit of <20 phycoerythrin molecules per particle. Data collected with the transit time reduced to 25 micros (in the same instrument but at 2.4 mW laser output) demonstrated a detection limit of approximately 75 phycoerythrin molecules and CVs of about 2.7%. The performance, cost, size, and power consumption of the tested laser pointer module suggests that it may be suitable for use in conventional flow cytometry, particularly if it were coupled with cytometers that support extended transit times.

“6 markers/5 colors” extended white blood cell differential by flow cytometry

Electronic white blood cell (WBC) differential by standard cytology (hematology analyzer and visual inspection of blood smears) is limited to five types and identification of abnormal cells is only qualitative, often problematic, poorly reproducible, and labour costing. We present our results on WBC differential by flow cytometry (FCM) with a 6 markers, 5 colors CD36-FITC/CD2-PE+CRTH2-PE/CD19-ECD/CD16-Cy5/CD45-Cy7 combination, on 379 subjects, with detection of 12 different circulating cell types, among them 11 were quantified. Detection of quantitative abnormalities of whole leucocytes, neutrophils, eosinophils, basophils, monocytes, or lymphocytes was comparable by FCM and by standard cytology in terms of sensitivity and specificity. FCM was better than standard cytology in detection and quantification of circulating blast cells or immature granulocytes, with a first lineage orientation in the former case. All cases of lymphocytosis, with lineage assignment, were detected by FCM. FCM identified a group of patients with excess of CD16pos monocytes as those having an inflammatory syndrome. WBC differential by FCM is at least as reliable as by standard cytology. FCM superiority consists in identification and systematic quantification of parameters that cannot be assessed by standard cytology such as lineage orientation of blast cells or lymphocytes, and expression of markers of interest such as CD16 on inflammatory monocytes.

An internal positive control for the enumeration of CD45(+) and CD34(+) cells by flow cytometry allows monitoring of reagent and operator performance

BACKGROUND

Three-color flow cytometry assays are used to determine CD34(+) cell doses prior to stem cell transplantation. These assays require high-quality reagents that are dispensed accurately to ensure reproducible results. We have developed a flow cytometry assay for CD34(+) cells with an integral positive control (KG1a cells) for monitoring reagent and operator performance.

METHODS

The method was validated using samples from 127 allogeneic donations (42 BM, 85 PBSC) from healthy donors and 195 autologous donations (46 BM, 149 PBSC) from patients in remission from hematologic malignancies. The mean, SD and range of CD45(+) and CD34(+)cell counts were determined for each donation type. An internal control was used to assess performance of reagents and operators by comparison with a predetermined target value and an experienced operator.

RESULTS

Replicate studies showed the method to be accurate and precise, with KG1a cells at 97.7+/-3.9% of the target value and a CV of 4.0%. In routine use over 322 samples, the accuracy was 91.7+/-17.7% of the target value, with a CV of 19.3%. Investigations into the cause of the reduced precision showed that reagents performed consistently well but operator performance was variable, with two of six operators significantly under-dispensing KG1a cells.

DISCUSSION

This study validates our three-color flow cytometry assay and demonstrates that KG1a cells may be used to monitor test performance in the routine working environment. In addition to monitoring performance within a single laboratory, its wider use in multicenter studies may be helpful regarding standardization of methods.

Diagnostic accuracy and clinical utility of a simplified low cost method of counting CD4 cells with flow cytometry in Malawi: diagnostic accuracy study

OBJECTIVES

To assess the diagnostic accuracy and clinical utility of a simplified low cost method for measuring absolute and percentage CD4 counts with flow cytometry.

DESIGN

A CD4 counting method (Blantyre count) using a CD4 and CD45 antibody combination with reduced blood and reagent volumes. Diagnostic accuracy was assessed by measuring agreement of the index test with two other assays (TruCount and FACSCount). Clinical utility was investigated by comparing CD4 counts with the new assay with WHO clinical staging in patients with HIV.

SETTING

Research laboratories and antiretroviral therapy clinic at a medical school and large government hospital in southern Malawi.

PARTICIPANTS

Assay comparisons were performed on consecutive blood samples sent for CD4 counting from 129 patients with HIV. Comparison of CD4 count with staging was conducted on 253 consecutive new patients attending the antiretroviral therapy clinic.

MAIN OUTCOME MEASURES

Limits of agreement with 95% confidence intervals between index test and reference standards.

RESULTS

The limits of agreement for Blantyre count and TruCount were excellent (cell count -48.9 to 27.0 x10(9)/l for absolute counts in the CD4 range <400x10(9)/l and -2.42% to 2.37% for CD4 percentage). The assay was affordable with reagent costs per test of $0.44 ( pound0.22, euro0.33) for both absolute count and CD4 percentage, and $0.11 for CD4 percentage alone. Of 193 patients with clinical stage I or II disease, who were ineligible for antiretroviral therapy by clinical staging criteria, 73 (38%) had CD4 counts <200x10(9)/l. By contrast, 12 (20%) of 60 patients with stage III or IV disease had CD4 counts >350x10(9)/l.

CONCLUSIONS

This simplified method of counting CD4 cells with flow cytometry has good agreement with established commercial assays, is affordable for routine clinical use in Africa, and could improve clinical decision making in patients with HIV.

In vitro micronucleus assay scored by flow cytometry provides a comprehensive evaluation of cytogenetic damage and cytotoxicity

This laboratory has previously reported on the development of a flow cytometry-based method for scoring in vitro micronuclei in mouse lymphoma (L5178Y) cells [S.L. Avlasevich, S.M. Bryce, S.E. Cairns, S.D. Dertinger, In vitro micronucleus scoring by flow cytometry: differential staining of micronuclei versus apoptotic and necrotic chromatin enhances assay reliability, Environ. Molec. Mutagen. 47 (2006) 56-66]. With this method, necrotic and mid/late stage apoptotic cells are labeled with the fluorescent dye ethidium monoazide. Cells are then washed, stripped of their cytoplasmic membranes, and incubated with RNase plus a pan-nucleic acid dye (SYTOX Green). This process provides a suspension of free nuclei and micronuclei that are differentially stained relative to chromatin associated with dead/dying cells. The current report extends this line of investigation to include the human cell line TK6. Additionally, methods are described that facilitate simultaneous quantitative analysis of cytotoxicity, perturbations to the cell cycle, and what we hypothesize is aneuploidization. This comprehensive cytogenetic damage assay was evaluated with the following diverse agents: etoposide, ionizing radiation, methyl methanesulfonate, vinblastine, ethanol, and staurosporine. Cells were harvested after 30h of continuous treatment (in the case of chemicals), or following graded doses of radiation up to 1Gy. Key findings include the following: (1) Significant discrepancies in top dose selection were found for five of the six agents studied when relative survival measurements were based on Coulter counting versus flow cytometry. (2) Both microscopy- and flow cytometry-based scoring methods detected dose-dependent micronucleus formation for the four genotoxic agents studied, whereas no significant increases were observed for the presumed non-genotoxicants ethanol and staurosporine when top dose selection was based on flow cytometric indices of cytotoxicity. (3) SYTOX and ethidium monoazide fluorescence signals conveyed cell cycle and cell death information, respectively, and appear to represent valuable aids for interpreting micronucleus data. (4) The frequency of hypodiploid nuclei increased in response to each of the genotoxic agents studied, but not following exposure to ethanol or staurosporine. Collectively, these results indicate that a comprehensive assessment of genotoxicity and other test article-induced toxicities can be acquired simultaneously using a simple two-color flow cytometry-based technique.

Evaluation of a single-platform microcapillary flow cytometer for enumeration of absolute CD4+ T-lymphocyte counts in HIV-1 infected Thai patients

BACKGROUND

Various assays are used to enumerate peripheral blood absolute CD4+ T-lymphocytes. Flow cytometry is considered the gold standard for this purpose. However, the high cost of available flow cytometers and monoclonal antibody reagents make it difficult to implement such methods in the resource-poor settings. In this study, we evaluated a cheaper, recently developed single-platform microcapillary cytometer for CD4+ T-lymphocyte enumeration, the personal cell analyzer (PCA), from Guava Technologies.

METHODS

CD4+ and CD8+ T-lymphocyte counts in whole blood samples from 250 HIV-1 infected Thais were determined, using a two-color reagent kit and the Guava PCA, and compared with the results obtained with two reference microbead-based methods from Becton Dickinson Biosciences: the three-color TruCOUNT tube method and the two-color FACSCount method. Statistical correlations and agreements were determined using linear correlation and Bland-Altman analysis.

RESULTS

Absolute CD4+ T-lymphocyte counts obtained using the Guava PCA method highly correlated with those obtained using TruCOUNT method (R(2) = 0.95, mean bias +13.1 cells/microl, limit of agreement [LOA]-117.9 to +144.1 cells/microl) and the FACSCount method (R2 = 0.94, mean bias = +33.2 cells/microl, LOA-101.8 to +168.3 cells/microl). Absolute CD8+ T-lymphocyte counts obtained using the Guava PCA method also highly correlated with those obtained with the two reference methods (R(2) = 0.92 and 0.88, respectively).

CONCLUSION

This study shows that the enumeration of CD4+ T-lymphocytes using the Guava microcapillary cytometer PCA method performed well when compared with the two reference bead-based methods. However, like the two reference methods, this new method needs substantial technical expertise.

Diagnostic relevance of the determination of lymphocyte subpopulations in environmental medicine

Earlier hopes that determination of lymphocyte subpopulations might become a strong diagnostic tool in environmental medicine have not been fulfilled in recent years. Analysis of the scientific literature rather shows that there are only few examples for environmental exposures causing reproducible shifts of lymphocyte subpopulations. Moreover, current knowledge suggests that "environmental diseases" are not associated with characteristic changes of subpopulation patterns. If lymphocyte subpopulations are analyzed, each diagnostic step, including indication, sample handling, analytic procedure and data-interpretation, should adhere to good quality criteria. Taking all together, the determination of lymphocyte subpopulations in the context of environmental medicine comes under category IV of the criteria of the Commission for Methods and Quality Assurance in Environmental Medicine of the German federal health authority (Robert Koch-Institute; RKI): "A procedure cannot be recommended because there is not sufficient information to justify it" (here: no solid trends in epidemiological examinations), "and because theoretical considerations speak against an application" (here: high physiological variability and missing exposure or substance specificity).

Flow cytometric assessment of autologous gammadelta T cells in patients with acute myeloid leukemia: potential effector cells for immunotherapy?

BACKGROUND

Gammadelta T cells are a rare component of the circulating innate immune system capable of exerting anti-neoplastic activity. This population may be suitable for the adoptive immunotherapy of acute myeloid leukemia (AML). Little is known however, about the frequency and function of circulating gammadelta T cells in AML. The aim of the study was to enumerate peripheral blood gammadelta T cells in patients with AML and explore the feasibility of their use clinically.

METHODS

We compared the absolute circulating gammadelta T cell levels in 33 AML patients before and after treatment versus 20 healthy volunteers using flow cytometry. The function of gammadelta T cells was assessed by detection of intracelluar interferon-gamma (IFN-gamma) and cytotoxicity against leukemic blasts.

RESULTS

AML patients with high blast counts prior to induction chemotherapy had marginally decreased gammadelta T cell levels compared with healthy controls: median 38/microL versus 83/microL; P = 0.051. Sequential gammadelta T cell enumeration after induction showed significantly decreased counts in patients with a persistently high blast burden compared to patients with reduced but detectable residual disease (molecular maker or borderline bone marrow infiltration): median 7/microL versus 105/microL; P = 0.008. Patients with residual disease had significantly higher gammadelta T cell counts compared to those retested after they had achieved complete remission (CR); P = 0.0025. In CR, gammadelta T cell counts remained lower than those of healthy individuals: median 33/microL versus 83/microL, P = 0.030. We detected a sharp increase (on average, four-fold higher than values in CR) of gammadelta T cells in patients in very early morphologic or molecular relapse. We also tested the functional properties of gammadelta T cells from patients with AML in CR. Flow cytometric assessment of IFN-gamma revealed similar numbers of gammadelta T cells expressing the T1 cytokine compared with healthy controls. We also showed that gammadelta T cells were able to kill leukemic target cells in vitro.

CONCLUSION

Flow cytometric assessment of gammadelta T cells in patients with AML revealed quantitative shifts with respect to disease status. Our data suggest that gammadelta T cells warrant further investigation as potential therapeutic agents.

Comparison of capillary based microflurometric assay for CD4+ T cell count estimation with dual platform Flow cytometry

The CD4+ T cell count estimation is an important monitoring tool for HIV disease progression and efficacy of anti-retroviral treatment (ART). Due to availability of ART at low cost in developing countries, quest for reliable cost effective alternative methods for CD4+ T cell count estimation has gained importance. A simple capillary-based microflurometric assay (EasyCD4 System, Guava Technology) was compared with the conventional flow cytometric assay for estimation of CD4+ T cell counts in 79 HIV infected individuals. CD4+ T cell count estimation by both the assays showed strong correlation (r = 0.938, p < 0.001, 95% CI 0.90 to 0.96). The Bland Altman plot analysis showed that the limits of variation were within agreeable limits of ± 2SD (-161 to 129 cells/mm³). The Easy CD4 assay showed 100% sensitivity for estimating the CD4+ T cell counts < 200 cells/mm³ and < 350 cells/mm³ and 97% sensitivity to estimate CD4+ T cell count < 500 cells/mm³. The specificity ranged from 82 to 100%. The Kappa factor ranged from 0.735 for the CD4+ T cell counts < 350 cells/mm³ to 0.771 for < 500 cells/mm³ CD4+ T cell counts. The system works with a simple protocol, is easy to maintain and has low running cost. The system is compact and generates minimum amount of waste. Hence the EasyCD4 System could be applied for estimation of CD4+ T cell counts in resource poor settings.

Affordable flow cytometry for enumeration of absolute CD4+ T-lymphocytes to identify subtype C HIV-1 infected adults requiring antiretroviral therapy (ART) and monitoring response to ART in a resource-limited setting

BACKGROUND

The World Health Organization (WHO)'s "3 x 5 program" has spurred efforts to place 3 million people on combination antiretroviral therapy (ART) for treatment of AIDS in resource-limited countries. Paradoxically, the cost of CD4+ T-lymphocyte count essential for decision-making to commence HIV positive adults on ART as well as for monitoring responses to ART remains unaffordable in most resource-limited countries. Thus, low-cost methods for enumerating CD4+ T-lymphocyte are urgently needed.

OBJECTIVE

To evaluate Cyflow cytometry (Cyflow SL, Partec, Munster, Germany) for enumeration of absolute CD4+ T-lymphocyte in subtype C HIV-1 seropositive subjects using FACSCount (Becton and Dickinson, Immunocytometry Systems, San Jose, CA, USA) as the "predicate method".

METHODS

A total of 150 HIV-1 seropositive subjects were included in the evaluation exercise. Fifty-eight specimens were collected from pregnant HIV-1 seropositive women (subtype C drug resistance study). Twenty-seven specimens were collected from women and their spouses with AIDS followed in a Duke ART study to assess the immunologic and virologic responses to generic ART, comprising Stavudine, Lamivudine and Nevirapine (Stalanev, Varichem Labs, Harare, Zimbabwe). Sixty-five specimens were collected from AIDS patients enrolled in an ongoing Kaposi Sarcoma (KS) study to investigate impact of ART on KS progression. Enumeration of CD4+ T-lymphocytes using FACSCount is routinely conducted for all the three studies. The Medical Research Council of Zimbabwe and Medicines Control Authority of Zimbabwe approved the studies. Whole blood was collected in EDTA vacutainer tubes and aliquoted into two tubes (200 microL in each). CD4+ T-lymphocyte counts were enumerated using a Cyflow counter, in the Department of Immunology and a FACSCount in the Department of Obstetrics and Gynaecology within 6 hours of phlebotomy following manufacturers' instructions.

RESULTS

Using linear regression analysis, there was a very strong correlation (R = 0.991) between the overall CD4+ T-lymphocyte counts obtained by FACSCount and those obtained by Cyflow. When data analysis was stratified by study groups, there was a strong correlation between the FACSCount and Cyflow CD4+ T-lymphocyte counts from subjects in the three independent studies; Subtype C resistance (R2 = 0.987), Duke ART (R2 = 0.980) and KS (R2 = 0.994), Table 1. Using Bland-Altman plots, the overall, absolute CD4+ T lymphocytes obtained by the two methods were in excellent agreement (mean difference 1.21, 95% Confidence Interval {CI): -2.1 to 3.3). For the 0-250 CD4+ T-lymphocytes range, the CD4 counts obtained using FACSCount were also in good agreement with those obtained using Cyflow counter (mean difference = 2.6 cells/microL, 95% CI: -1.1 to 6.3). Similarly, in the 251-500 (mean difference 1.0, cells/microL, 95% CI: -3.7 to 5.6) and the 501-1200 (mean difference = 0.29 cells/microL, 95% CI: -8.1 to 8.7) CD4 T-lymphocytes range, good agreement was observed.

CONCLUSION

The Cyflow counter is as accurate as the FACSCount in enumerating absolute CD4+ T-lymphocytes in the range 1-1200 cells/muL. Cyflow cytometry is relatively affordable, easy to use technology that is useful not only in identifying HIV seropositive individuals who require ART but also for monitoring immunologic responses to ART.

Flow rate calibration. III. The use of stabilized biostandards to calibrate the flow rate and calculate absolute CD4+ T-cell counts

BACKGROUND

We have previously reported a flow rate calibration method for the determination of absolute CD4(+) T-lymphocyte counts that removes the need for the addition of latex beads to each sample. However, a limitation with this approach is that a calibration factor (CF) needs to be applied to adjust for differences in viscosity between latex bead suspensions and biological specimens. We have also demonstrated the value of using stabilized whole blood samples in external quality assessment (EQA) studies; such samples have a stable absolute lymphocyte count for over 1 year, at 4 degrees C. It was successfully demonstrated that this material can be used as a flow rate biocalibration (FRB) material for use as a flow cytometric control to provide a sample with a known CD4(+) T-lymphocyte count. Such material has advantages over latex bead technology as it can act as a full process control as well as having the same matrix and viscosity characteristics as the test material, thus removing the need for a CF.

METHODS

In this study, we have analyzed 268 consecutive normal, abnormal, and HIV(+) samples using FRB, incorporating the PanLeucoGating approach and compared this to the MultiSet method, defined as the predicate.

RESULTS

Percentage similarity statistics revealed the following: 0-3,000 CD4(+) cells/mul mean percentage difference (MPD; bias) 1.2%, 95% CI of 5.6-8%; 0-200 CD4(+) cells/microl MPD of 1.25%, 95% CI of 11.63-14.13%; 201-500 CD4(+) cells/microl MPD of 1%, 95% CI of 4.6-6.6%.

DISCUSSION

This study demonstrates that stabilized whole blood can be used for FRB. It has the advantage of being a full process control, in addition to costing less than latex beads with highly comparable results. As bench top flow cytometers are extremely stable, this is a low cost and robust alternative to bead based methods for generating absolute CD4 counts.

Immunomagnetic cell selection performed for HLA haploidentical transplants with the CliniMACS device: effect of additional platelet removal on CD34+ cell recovery

Immunomagnetic CD34+ cell selection (ICS) is a widely employed technology in autotransplant and allotransplant settings. When an haploidentical transplant is performed, a high dose of purified CD34+ cells together with efficient T and B cell depletion are required to minimize the risks of graft versus host disease (GVHD) and Epstein-Barr virus (EBV)-related lymphoma. To ameliorate the performances of the CliniMACS (Miltenyi Biotec) ICS device, we compared 73 ICS performed following the manufacturer's recommended platelet depletion versus 48 performed after adjunctive centrifugations to increase platelet depletion of the leukapheresis (LKF) product. A total of 121 ICS (from single or fractioned LKF products) were carried out on 93 LKF collected from 47 related healthy donors. A statistical significance in terms of CD34+ cell recovery (81.8% vs. 71.2%) was found in favor of the modified ICS procedure (p=0.0049) with a comparable stem cell purity and viability. The modification of the standard manufacturer's technique for increasing platelet depletion can further improve the recovery of stem cells with no influence on T and B cell depletion. These results demonstrate the negative influence exerted on CD34+ cell recovery by LKF platelet contamination.

Panning of multiple subsets of leukocytes on antibody-decorated poly(ethylene) glycol-coated glass slides

The antibody (Ab) array format provides a unique opportunity to pan and characterize multiple leukocyte subsets in parallel. However, the questions of reproducibility and robustness of leukocyte panning on Ab arrays need to be answered for this technology to become an immunophenotyping tool. The present study sought to address several of these questions, including: (1) purity of leukocyte subsets captured on Ab regions, (2) dynamics of leukocyte binding, (3) elimination of non-specific cell adhesion, and (4) standardization of cell washing conditions. Abs for CD4 T-cells, CD8 T-cells, CD36 monocytes, and CD16b neutrophils were dispensed onto standard glass slides containing a thin film of poly(ethylene glycol) (PEG) hydrogel. PEG gel coating was highly effective in eliminated non-specific cell adhesion on the surface. Incubation of the Ab arrays with red blood cell (RBC) depleted whole blood resulting in antigen-specific panning of leukocyte subsets on the respective Ab domains. A flow through chamber was employed to determine optimal shear stress conditions for removal of non-specifically attached cells. The purity of the four subsets remaining on the surface after washing was determined by Wright staining and immunofluorescence, and was found to be as follows: CD4 T-cells (99.2+/-0.3%), CD8 T-cells (98.7+/-0.3%), CD36 monocytes (97.2+/-0.9%), and CD16b neutrophils (99.1+/-0.6%). In conclusion, the methods described in this study allow to separate whole blood into pure leukocyte subsets with minimal sample preparation and handling. These approaches will be valuable in the future development of Ab arrays as tools for quantitative immunophenotyping of leukocytes.

The Impact of Erythrocyte Lysing Procedures on the Recovery of Hematopoietic Progenitor Cells in Flow Cytometric Analysis

Since preanalytic lysing of erythrocytes remains critical in flow cytometry, we investigated the influence of four lysing procedures on the quantification of leukocyte and CD34+ cells in hematopoietic cell transplants (HCTs). Samples were derived from stem cell-enriched mobilized whole blood collected by apheresis (unselected) and immunologically purified stem cell products (selected) and were measured using the dual-platform (2-PF) method with two flow cytometric systems. Additionally, cells were measured by a volume-based technique (single platform [1-PF]). Results were identical in the 2-PF mode (unselected HCTs, r = 0.998; selected HCTs, r = 0.999). In comparison with the 2-PF results, the single-platform (1-PF) measurements revealed a mean decrease of 59.5% for CD34+ cells (50.8% for CD45+ cells) in unselected HCTs and a mean decrease of 52% for CD34+ cells (49.8% for CD45+ cells) in selected HCTs. In order to check the accuracy of cell quantification using the 1-PF method, leukocyte reference values from hematology counter results were compared with flow cytometric (1-PF)-counted nucleated cells. That analysis revealed good congruency, with r = 0.998 for unselected HCTs and r = 0.999 for selected HCTs. In conclusion, all lysing procedures that we used induced substantial loss of leukocytes and CD34+ cells. As demonstrated by the high accuracy of the 1-PF technique, all erythrocyte lysing procedures caused significant cell loss, which led to inconsistent counting of CD34+ cells in nonvolumetric flow cytometric (2-PF) protocols.

A simplified flow cytometry method of CD4 and CD8 cell counting based on thermoresistant reagents: implications for large scale monitoring of HIV-infected patients in resource-limited settings

OBJECTIVE

To validate a simplified flow cytometry assay for CD4 and CD8 T cell counting based on monoclonal antibodies which are made resistant to high temperatures (simplified thermoresistant assay (STRA)).

METHOD

The STRA employs FITC-conjugated anti-CD4 and anti-CD8 monoclonal antibodies, predispensed into test tubes and chemically treated to be resistant to high temperatures. Five correlation studies were performed in three different laboratories on a total of 560 blood samples from HIV-1 infected patients. Each study correlated the STRA with either double or single platform assays currently available. Accelerated stability tests on the FITC-conjugated monoclonal antibodies were performed to assess the resistance of the STRA to high temperatures.

RESULTS

Comparison of STRA with both single platform and double platform assays gave correlation coefficients ranging 0.957-0.987 for CD4+ T cells and 0.946-0.968 for CD8+ T cells. In all correlation studies there was a perfect data overlapping in the low-pathological interval of CD4+ T cells (0-400 cells/ml). The FITC-conjugated CD4 and CD8 monoclonal antibodies maintained intact binding activity and fluorescence brightness after storage for 4 weeks at 45 degrees C and can be stored for up to 8 years in regular conditions (+4 degrees C).

CONCLUSIONS

The STRA correlates well with both single-platform and double-platform flow-cytometry assays currently used to assess CD4+ T cells. The test procedure is simple, rapid, and easy to perform. The reagents can be stored under unfavorable environmental conditions for long period of time. These features should facilitate access to flow cytometry testing in resource-poor settings.

In vitro micronucleus scoring by flow cytometry: differential staining of micronuclei versus apoptotic and necrotic chromatin enhances assay reliability

The in vitro micronucleus test has received considerable attention in recent years for its use in drug safety assessment and toxicological research. The less tedious nature of the assay relative to chromosome aberration analyses is a driving force, and explains why many chemical and drug safety programs have adopted the endpoint. Development of a high-throughput micronucleus scoring system would further enhance the utility of the assay for lead optimization and other early drug development work. Although several variations of a flow cytometric (FCM) method for scoring cell-culture-derived micronuclei (MN) have been described in the literature, they have been unable to distinguish true MN from apoptotic and necrotic chromatin (Nüsse M and Marx K 1997: Mutat Res 392: 109-115). Here, we report advances to this methodology whereby a sequential staining procedure is used to differentially label these types of sub-2n particles. With the use of ethidium monoazide (EMA), the chromatin of dead and dying cells is labeled. After a photoactivation step that covalently binds EMA to chromatin, cytoplasmic membranes are digested and resulting lysates are incubated with RNase plus a pan-nucleic acid dye (SYTOX Green). This process provides a suspension of free nuclei and sub-2n particles that are labeled with either SYTOX or SYTOX and EMA. Preliminary studies with heat-shocked L5178Y mouse cells demonstrated that EMA stains necrotic and mid- through late-stage apoptotic cells. Importantly, the sequential labeling procedure provided reliable micronucleus enumeration, even when cultures contained high percentages of dead cells. Subsequently, experiments with the following diverse genotoxicants were performed: hydroxyurea, methyl methanesulfonate, benzo[a]pyrene, etoposide, cyclophosphamide, and vinblastine. Additionally, the nongenotoxicants sucrose, tributyltin methoxide, and dexamethasone were tested up to 5 mg/ml, or to cytotoxic concentrations. FCM data were found to correspond closely with microscopy-based measurements. Collectively, these data suggest that this sequential EMA/SYTOX staining procedure provides reliable, high-throughput enumeration of in vitro MN.

Clinical impact of a new automated system employed for peripheral blood stem cell collection

At the moment, PBSC collections can be performed using semi-automated or automated cell separator devices. The automated methods offer the advantages of a decreased working load for dedicated personnel and high standardization of the collection procedure. Herein we report our single institutional experience in 80 PBSC collections employing the new automated COM.TEC Fresenius autoMNC program that provides the ability to predict the total number of CD34(+) cells collected, based on the pre-leukapheresis CD34(+) cell count in peripheral blood. Fourty-eight patients and 21 healthy donors were mobilized with chemotherapy + G-CSF or G-CSF alone, respectively. Eighty leukapheresis collections were performed starting with a CD34(+) cell count in peripheral blood at least of 20/microL. Collection parameters and related side effects were evaluated. The mean CD34(+) cell collection efficiency in patients and donors was 81.8% (sd 27.6) and 95.1% (sd 15.6), respectively. The mean difference between real and predicted CD34(+) cells was +30.2% (sd 92.9) for patients and +4.6% (sd 30.3) for donors. The mean leukapheresis bag volume was 240.7 ml (sd 67.3) and 310.3 ml (sd 86.8) with a mean HCT of 10.9% (sd 34.4) and 9.2% (sd 3.9) for patients and donors, respectively. The automated PBSC collection with the new program COM.TEC Fresenius autoMNC demonstrated a very high CD34(+) cell collection efficiency. Moreover, the ability to predict the CD34(+) cell yield permits improved management of the leukapheresis collection, with the only disadvantage of larger leukapheresis volume and higher hematocrit.

Comparison of disruption procedures for enumeration of activated sludge floc bacteria by flow cytometry

BACKGROUND

In a wastewater treatment plant, the degradation process is performed by a variable and mixed community of microorganisms in an aerobic aquatic environment. The activated-sludge process is based on the formation of strong microbial flocs where many bacteria are attached to sludge flocs.

METHODS

Cytometric analysis requires an homogeneous cell suspension and so detachment of bacteria from flocs is required. In this study, sonication and homogenization were compared to find the most adequate pretreatment method for bacterial cytometric analysis in activated sludge samples. Bacterial viability was tested with a nucleic acid double-staining (NADS) protocol (Barbesti et al., Cytometry 2000;40:214-218) and on flow cytometry.

RESULTS

Each method showed a good efficiency in terms of bacterial detachment; thus finally, the choice of which could be the best treatment method was based on both viability results and analysis rapidity. On the basis of the degree of cell detachment and viability, the maximum value was obtained by sonication (2 x 45'').

CONCLUSIONS

The use of flow cytometry in conjunction with fluorescent dyes and an adequate pretreatment represents a useful method to rapidly detect and enumerate bacteria in activated sludge samples.

Relation between JAK2 (V617F) mutation status, granulocyte activation, and constitutive mobilization of CD34+ cells into peripheral blood in myeloproliferative disorders

We studied the relationship between granulocyte JAK2 (V617F) mutation status, circulating CD34(+) cells, and granulocyte activation in myeloproliferative disorders. Quantitative allele-specific polymerase chain reaction (PCR) showed significant differences between various disorders with respect to either the proportion of positive patients (53%-100%) or that of mutant alleles, which overall ranged from 1% to 100%. In polycythemia vera, JAK2 (V617F) was detected in 23 of 25 subjects at diagnosis and in 16 of 16 patients whose disease had evolved into myelofibrosis; median percentages of mutant alleles in these subgroups were significantly different (32% versus 95%, P < .001). Circulating CD34(+) cell counts were variably elevated and associated with disease category and JAK2 (V617F) mutation status. Most patients had granulocyte activation patterns similar to those induced by administration of granulocyte colony-stimulating factor. A JAK2 (V617F) gene dosage effect on both CD34(+) cell counts and granulocyte activation was clearly demonstrated in polycythemia vera, where abnormal patterns were mainly found in patients carrying more than 50% mutant alleles. These observations suggest that JAK2 (V617F) may constitutively activate granulocytes and by this means mobilize CD34(+) cells. This exemplifies a novel paradigm in which a somatic gain-of-function mutation is initially responsible for clonal expansion of hematopoietic cells and later for their abnormal trafficking via an activated cell progeny.

Evaluation of a new single-parameter volumetric flow cytometer (CyFlow(green)) for enumeration of absolute CD4+ T lymphocytes in human immunodeficiency virus type 1-infected Thai patients

Use of the standard dual-platform flow cytometric method for determination of CD4(+) T-lymphocyte counts, which needs both a flow cytometer (FCM) and hematological analyzer, would inevitably lead to increased variability. The development of new single-platform (SP) FCMs that provide direct CD4(+) T-lymphocyte counts for improved assay precision and accuracy have recently attracted attention. This study evaluated one of those systems, CyFlow(green) (Partec), a single-parameter SP volumetric FCM. The performance of CyFlow(green) was compared with those of two reference standard SP microbead-based technologies of the three-color TruCOUNT tube with the FACScan FCM and a two-color FACSCount system (Becton Dickinson Biosciences). Absolute CD4(+) and CD8(+) T-lymphocyte counts in 200 human immunodeficiency virus type 1-seropositive blood specimens were determined. Statistical analysis for correlation and agreement were performed. A high correlation of absolute CD4 counts was shown when those obtained with CyFlow(green) were compared with those obtained with the bead-based three-color TruCOUNT system (R(2)=0.96; mean bias, -69.1 cells/microl; 95% confidence interval [CI], -225.7 to+87.5 cells/microl) and the FACSCount system (R(2)=0.97; mean bias, -40.0 cells/microl; 95% CI, -165.1 to+85.1 cells/microl). The correlation of the CD4(+) T-lymphocyte counts obtained by the two bead-based systems was high (R(2)=0.98). Interestingly, CyFlow(green) yielded CD4(+) T-lymphocyte counts that were 21.8 and 7.2 cells/microl lower than those obtained with the TruCOUNT and the FACSCount systems, respectively, when CD4(+) T-lymphocyte counts were <250 CD4(+) T-lymphocyte counts/microl range or 17.3 and 5.8 cells/microl less, respectively, when CD4(+) T-lymphocyte counts were <200 cells/microl. The single-parameter CyFlow(green) volumetric technology performed well in comparison with the performance of the standard SP bead-based FCM system. However, a multicenter comparative study is needed before this FCM machine is implemented in resource-limited settings.

Peripheral blood progenitor cell mobilization and collection in 42 patients with primary systemic amyloidosis

BACKGROUND

High-dose chemotherapy followed by an inoculum of autologous peripheral blood progenitor cells (PBPCs) can improve survival in patients affected with primary systemic amyloidosis (AL). It has been documented, however, that the morbidity and mortality of PBPC mobilization and collection in this setting are higher than in patients with other diseases. To minimize the mobilization and collection-related risks, we developed a multidisciplinary approach involving different specialists to manage AL patients with predominant heart and renal involvement.

STUDY DESIGN AND METHODS

We report our experience in 42 patients (23 men, 19 women; median age, 51.2 years; range, 28-68 years) with AL who underwent PBPC mobilization and collection. Twenty of the 42 patients (47.6%) had cardiac involvement and 35 of 42 (83.3%) renal involvement. Thirty-three patients (78.5%) were mobilized with granulocyte-colony-stimulating factor (G-CSF) alone (10 microg/kg) and 9 (21.4%) with cyclophosphamide (CTX) (3 g/m(2)) plus G-CSF (10 microg/kg).

RESULTS

The median number of collections per patient after either G-CSF or CTX plus G-CSF was 1.8 (range, 1-3). The median number of CD34+ cells collected in patients mobilized with G-CSF alone was 8.2 x 10(6) per kg (range, 1.35 x 10(6)-21.3 x 10(6)/kg) and in patients mobilized with CTX plus G-CSF it was 8.9 x 10(6) per kg (range, 5.5 x 10(6)-14.9 x 10(6)/kg). Forty of the 42 (95.2%) patients produced the minimum required CD34+ cell target dose (4 x 10(6)/kg). The overall rate of morbidity during the collections was 50 percent (21/42 patients): 18 patients (42.8%) had asymptomatic hypotension, 1 (2.4%) had symptomatic hypotension with nausea and vomiting, and 2 (4.7%) experienced a life-threatening hypotensive episode. There were no procedure-related deaths.

CONCLUSION

Our multidisciplinary approach was effective in limiting the serious side effects related to PBPC mobilization and collection in AL patients.

Multicentre evaluation of stable reference whole blood for enumeration of lymphocyte subsets by flow cytometry

BACKGROUND: Clinical indications for lymphocyte subset enumeration by flow cytometry include monitoring of disease progression and timing of therapeutic intervention in infection with human immunodeficiency virus. Until recently international standardisation has not been possible due to a lack of suitable stable reference material. METHODS: This study consisted of two trials of a stabilised whole blood preparation. Eleven participants were sent two standard protocols for staining plus gating strategy and asked to report absolute counts for lymphocyte subsets. RESULTS: No significant difference was detected between the two methods when results from the two assays and all partners were pooled. Significant differences in results from the different partners were observed. However, representative mean counts were obtained for geometric means, geometric coefficient of variation, and 95% confidence interval for CD3 910 cells/mul, 9%, and 888 to 933, respectively), CD4 (495 cells/mul, 12%, and 483 to 507), and CD8 (408 cells/mul, 13%, and 393 to 422). CONCLUSION: We have introduced a stabilised blood preparation and a well-characterized biological standard. The availability of this reference material greatly simplifies the validation of new techniques for CD4(+) T-cell enumeration and the expansion of external quality assurance programmes for clinical laboratories, including those that operate in resource-restricted environments. (c) 2005 Wiley-Liss, Inc.

Recovery of viable CD34+ cells from cryopreserved hemopoietic progenitor cell products

The number of CD34+ cells infused into patients at the time of autologous or allogeneic transplantation is a clinically important variable, but the viability of these cells has not been extensively documented. In this study, we analyzed the recovery of viable CD34+ cells before and after cryopreservation on 79 autologous stem cell products, using a novel flow cytometry assay without red cell lysis. For 70 PBSC harvest samples, the mean viable CD34+ cell count was 5.98 x 10(6)/kg (range 0.3-23 x 10(6)/kg) before freezing and 5.4 x 10(6)/kg (range 0.2-23 x 10(6)/kg) after thawing. The median recovery was 93% (range 48-107%), with 90% recovery for NHL (range 48-100%, n=34), 83% for multiple myeloma (range 56-106%, n=11), 92.3% for acute leukemia (range 71-100% n=7) and 94.5% for nonhematological malignancies (range 50-107% n=18). Similarly, for autologous bone marrows (n=9) the median recovery of viable CD34+ cells was 90% (range 68-100%). The recovery of viable CD34+ cells for adult (n=51) and pediatric (n=28) stem cell collections was 91 and 94%, respectively. Further examination of the correlation between the kinetics of hematological recovery and the number of viable progenitor cells infused, particularly at the lower end of the accepted dose range, may be warranted.

Low CD4+ T-lymphocyte values in human immunodeficiency virus-negative adults in Botswana

CD4+-lymphocyte counts (LCs) play a crucial role in the management and monitoring of HIV infection. Variability in CD4+ LCs has been reported to occur as a result of measurement techniques and/or biological variations. We report on the CD4+ LCs of healthy human immunodeficiency virus (HIV)-seronegative adults in Botswana. Samples were obtained from HIV-seronegative blood donors. The median CD4+ LC was 726 cells/mm3 (for females, 782 cells/mm3; for males, 698 cells/mm3). The median CD8+ LC was 488 cells/mm3 (for females, 494 cells/mm3; for males, 485 cells/mm3). The median CD4+-to-CD8+ ratio was 1.57 (for females, 1.66; for males, 1.51). Our findings of low CD4+ LCs among HIV-negative adults in Botswana are significant and have important implications for the management of HIV disease in the population of this sub-Saharan African country.

Absolute CD4 T-Cell Counting in Resource-Poor Settings

Flow cytometry is an accurate but expensive method to determine absolute CD4 cell counts. We compared different methods to measure absolute CD4 counts in blood samples from HIV-infected and uninfected subjects using a research/clinical flow cytometer (FACScan); a dedicated clinical instrument (FACSCount); and a volumetric, mobile, open-system flow cytometer equipped with 3 fluorescence and 2 light scatter detectors (Cyflow SL blue). The FACScan and Cyflow were used as single-platform instruments, but they differ in running cost, which is a central factor for resource-poor settings. Direct volumetric and bead-based CD4 measurements on the Cyflow were compared with 2 bead-based single-platform CD4 measurements on the FACSCount and on FACScan (TruCount) in "Le Dantec" Hospital, Dakar, Senegal, using whole blood samples from 102 HIV+ and 28 HIV- subjects. The agreement between the various measurement methods was evaluated by Bland-Altman analysis. Volumetric CD4 measurements on the Cyflow using a no-lyse-no-wash (NLNW) procedure and a lyse-no-wash (LNW) procedure correlated well with each other (R2 = 0.98) and with CD4 measurements on the FACSCount (R2 = 0.97) and FACScan (R2 = 0.97), respectively. Red blood cell lysis had no negative effect on the accuracy of absolute CD4 counting on the Cyflow. An excellent correlation was observed between bead-based CD4 measurements on the Cyflow and CD4 measurements on the FACSCount (R2 = 0.99) and FACScan (R2 = 0.99). Rigid internal and external quality control monitoring and adequate training of technicians were considered essential to generate accurate volumetric CD4 measurements on the Cyflow.

Flow cytometry evaluation of erythroid and myeloid dysplasia in patients with myelodysplastic syndrome

The purpose of this study was to develop a flow cytometric approach to the evaluation of marrow dysplasia in myelodysplastic syndromes (MDS). We first studied a cohort of 103 MDS patients as well as 46 pathological and healthy controls. Flow cytometry data were expressed as percentage of positive cells. Analysis of erythroid cells showed higher proportions of immature cells (P < 0.001) and decreased levels of CD71 expression on nucleated red cells (P = 0.02) in MDS. Analysis of myeloid cells showed lower proportions of CD10+ and higher proportions of CD56+ granulocytes (P < 0.001), and increased ratios of immature to mature cells (P = 0.007). Since no single immunophenotype could accurately differentiate MDS from other conditions, we used discriminant analysis for generating erythroid and myeloid classification functions using combinations of immunophenotypic parameters. These functions were prospectively validated in a testing cohort of 69 MDS patients and 46 pathological controls. A diagnosis of MDS was obtained in 60/69 cases (87%). No false-positive results were noticed among controls. Significant correlations between values of these functions and both degree of morphological dysplasia and the International Prognostic Scoring System were found. These findings indicate that flow cytometry evaluation of marrow dysplasia is feasible and may be useful in the work-up of individual MDS patients.

Impact of leukapheresis cell composition on immunomagnetic cell selection with the Baxter Isolex 300i device: a statistical analysis

Immunomagnetic cell selection (ICS) of CD34(+) cells is increasingly adopted in allogeneic and autologous transplant settings. Because many variables can affect the final results of ICS, we focused our study toward the influence exerted by the leukapheresis (LKF) cell composition on recovery, purity, and log of T and B depletion of the immunoselected cells. A total of 39 consecutive CD34(+) ICS were performed with the Isolex 300i (Baxter) device on 39 LKF from 9 HLA haploidentical donors and 20 patients. Flow cytometric analysis was performed both on the leukapheresis content and on the immunoselected cells. The statistical analysis was performed utilizing the Pearson's correlation test and the Mann-Whitney U test. The median purity and recovery of the immunoselected CD34(+) cells were 95.3% (IR: 93.0-99.0) and 55.1% (IR: 41.8-68.2), respectively. The median log of T and B depletion were 3.87 (IR: 3.5-4.3) and 2.9 (IR: 2.5-3.5), respectively. Our data indicate that not only the CD34(+) cell load but also the ratio among the cells belonging to the starting fraction can influence the results of ICS. LKF collection protocols have to be addressed to collect an high number of CD34(+) cells (>500 x 10(6)) without taking care of the contaminating cells when the Baxter Isolex 300i device is employed.

Modified Dynabeads Method for Enumerating CD4+ T-Lymphocyte Count for Widespread Use in Resource-Limited Situations

The Dynabeads method showed the potential for enumerating CD4 T lymphocytes (CD4 count) in HIV-1-infected individuals. The large volume of Dynabeads required for 1 sample and complex procedure made the method expensive and not easy for use, however. To decrease the cost and simplify the procedure, we reduced the volume of the Dynabeads, added wash times, and skipped over the staining step so as to count the CD4 cells directly under an optical microscope. The CD4 count of 246 blood samples using our modified Dynabeads method (DynabeadsCD4) showed a significant correlation with that obtained by flow cytometry (FlowcytoCD4) (r = 0.91 [P < 0.0001]; slope = 1.03, intercept = -16). The sensitivity and specificity for a CD4 count less than 200 cells/microL were 79% and 94%, and for a CD4 count less than 350 cells/microL, the sensitivity and specificity were 95% and 88%, respectively. The positive and negative predictive values for a CD4 count less than 350 cells/microL were 97% and 83%, respectively. The systematic error was 8 cells/microL (95% confidence interval [CI]: 0.4-16). The cost of Dynabeads for 1 sample was less than $1.00; thus, the estimated cost per DynabeadsCD4 test is less than $3.00, including the cost of other disposable materials. Our modified method is simple, economic, and accurate enough to monitor antiretroviral therapy in resource-limited situations.

Decreased absolute counts of T lymphocyte subsets and their relation to disease in squamous cell carcinoma of the head and neck

PURPOSE

Apoptosis of circulating CD8+ T cells seen in patients with squamous cell carcinoma of the head and neck [SCCHN (Hoffmann T, et al. Clin Cancer Res 2002;8:2553-62)] suggested a possibility of lymphocyte imbalance. Therefore, absolute numbers and percentages of lymphocyte subsets were examined in the peripheral blood of SCCHN patients and controls.

EXPERIMENTAL DESIGN

Venous blood was obtained from 146 patients with SCCHN and 54 normal volunteers. Absolute numbers of CD3+, CD4+, and CD8+ T lymphocytes were determined using fluorobeads in a flow cytometry-based technique. Percentages of T lymphocyte subsets were also evaluated by flow cytometry. The patients were grouped at the time of blood draw [active versus no evidence of disease (NED), type of therapy administered, and the length of follow-up].

RESULTS

Patients with SCCHN had significantly lower absolute numbers of CD3+ CD4+, and CD8+ T cells than normal controls. However, no differences in the percentages of T-cell subsets between patients and normal controls were observed. Patients with active disease had significantly lower CD3+ and CD4+ T-cell counts than those with NED. Patients who had NED after surgery and radiotherapy had the lowest T-cell counts among the NED cohort. Patients who had NED for >2 years did not recover their T-cell counts, and the T-cell imbalance was evident many years after curative surgery. The tumor-node-metastasis (TNM) stage or site of the disease was not related to the absolute T-cell count. Patients with recurrent disease at the time of blood draw tended to have the lowest CD4+ T-cell counts.

CONCLUSIONS

Patients with SCCHN have altered lymphocyte homeostasis, which persists for months or years after curative therapies.

Perfect count: a novel approach for the single platform enumeration of absolute CD4+ T-lymphocytes

BACKGROUND

The derivation of reliable CD4(+) T lymphocyte counts is vital for the monitoring of disease progression and therapeutic effectiveness in HIV(+) individuals. Flow cytometry has emerged as the method of choice for CD4(+) T lymphocyte enumeration, with single-platform technology, coupled with reference counting beads, fast becoming the "gold standard." However, although single-platform, bead-based, sample acquisition requires the ratio of beads to cells to remain unchanged, there is no available method, until recently, to monitor this.

METHODS

Perfect Count beads have been developed to address this issue and to incorporate two bead populations, with different densities, to allow the detection of inadequate mixing. Comparison of the relative proportions of both beads with the manufacture's defined limits enables an internal QC check during sample acquisition. In this study, we have compared CD4(+) T lymphocyte counts, obtained from 104 HIV(+) patients, using TruCount beads with MultiSet software (defined as the predicated method) and the new Perfect Count beads, incorporating an in house sequential gating strategy.

RESULTS

We have demonstrated an excellent degree of correlation between the predicate method and the Perfect Count system (r(2) = 0.9955; Bland Altman bias +27 CD4(+) T lymphocytes/microl).

CONCLUSIONS

The Perfect Count system is a robust method for performing single platform absolute counts and has the added advantage of having internal QC checks. Such an approach enables the operator to identify potential problems during sample preparation, acquisition and analysis.

Multicenter evaluation of two flow cytometric methods for counting low levels of white blood cells

BACKGROUND

Flow cytometric methods can be used to count residual white blood cells (WBCs) in WBC-reduced blood products, which should contain fewer than 1 x 10(6) WBCs per unit (approximately 3.3 WBCs/ microL). In this study two flow cytometric methods for counting WBCs under routine conditions in nine laboratories were evaluated.

STUDY DESIGN AND METHODS

Panels of red blood cells (RBCs), platelets (PLTs), and plasma were prepared containing 33.3, 10.0, 3.3, 1.0, and 0.3 WBCs per microL and counted with flow cytometric methods (either LeucoCOUNT, BD Biosciences, four laboratories; or LeukoSure, Beckman Coulter, five laboratories). Requirements were that at the level of 3.3 WBCs per microL, coefficient of variation was < or =20 percent and accuracy was > or =80 percent. Routine flow cytometric quality control (QC) data of WBC-reduced blood products from two laboratories were analyzed.

RESULTS

At the level of 3.3 WBCs per microL, none of the laboratories met the requirements for all three blood products. The LeucoCOUNT method met requirements at more laboratories than the LeukoSure method for RBCs and PLTs, but the opposite was true for plasma. Routine QC data showed that >99 percent of the flow cytometric measurements for WBC-reduced products was below the 95 percent prediction interval at 3.3 WBCs per microL.

CONCLUSION

None of the laboratories met the requirements for accuracy and precision for all three blood products. Nevertheless, routine results showed that in >99 percent of the products, WBC counts were below guideline limits. Therefore, both flow cytometric methods are suitable for QC with pass-fail criterion.

A new automated cell washer device for thawed cord blood units

BACKGROUND

The current available techniques to wash out DMSO from thawed umbilical cord blood (UCB) units are based essentially on standard centrifugation in an open system with various degrees of cell loss.

STUDY DESIGN AND METHODS

We evaluated the capacity of a new automated closed device (Cytomate, Baxter, IL) to wash out the DMSO from thawed UCB units, saving at the same time the progenitor and accessory cells in terms of CD34+ cells and MNCs. We modified the standard software of the device and calculated the cell recovery on 25 UCB units. Moreover, we set up a new gas chromatographic method to exactly detect the DMSO removal rate.

RESULTS

To evaluate the efficiency of the Cytomate device, we considered the postthawing (prewashing) versus postwashing cell recovery. The average recovery (%) in terms of total nucleated cells was 63.30 (range, 40.12-89.00), CD34+ cells was 70.20 (range, 11.51-89.01), CD3+ cells was 61.01 (range, 28.80-87.08), CD4+ cells was 62.53 (range, 30.62-96.73), CD8+ cells was 57.4 (range, 26.87-94.72), CD19+ cells was 63.33 (range, 39.10-90.33), CD16+/56+ cells was 70.67 (range, 8.91-98.40), CFU-GM was 74.33 (range, 20.23-98.60), total CFUs was 82.34 (range, 14.83-247.12), and viability was 89.67(range, 70.74-98.30). The total working time required was, on average, 15 minutes (range, 7-20).

CONCLUSIONS

The Cytomate device demonstrated a satisfying efficiency in cell recovery and in maintaining the clonogenic power of the UCB graft. The removal rate of DMSO was practically complete with evident advantages for the recipient. Finally, the entire manipulation performed in a closed system revealed to be safe, maintaining the sterility of the graft.

A flow cytometric method for determination of absolute counts of myeloid precursor dendritic cells in peripheral blood

Circulating precursor dendritic cells (pDCs) constitute a rare population in peripheral blood. They have a typical immunophenotypic profile, yet, they cannot be identified by pDC-specific immunophenotypic markers and therefore, their accurate and absolute enumeration poses a challenge. Here, we report a method for the evaluation of absolute counts of myeloid pDC in minimally manipulated blood samples on a flow cytometer as a single platform. Three-color flow cytometry was done to identify myeloid pDC as CD33+ HLA-DR+ CD14/CD16(dim/negative) cells in commercially available TruCount trade mark tubes that contain a defined number of brightly fluorescent polystyrene beads. The normal range in peripheral blood of 41 healthy adults, as determined by this single-platform method, was 17.0+/-5.7 x 10(6)/l, or 0.64+/-0.23% of mononuclear cells (MNCs). In parallel experiments, we have compared our procedure with two published 'dual-platform' methods that derive the absolute pDC count from a relative number obtained by flow cytometry, and from absolute counts obtained from a haematological analyser. Regression analysis showed an excellent correlation between results obtained with our single-platform protocol and these double-platform procedures (R2 > or = 0.90). However, the values obtained by the single-platform method were significantly higher than those obtained by the dual-platform methods. The higher myeloid pDC numbers in this single-platform procedure are likely due to reduced cell loss in this 'lyse-no-wash' protocol compared with the other methods which include density gradient separation and centrifugation steps. The intra- and interassay variability were 4.4% (range, 2.04-8.96%) and 5.8% (range, 2.59-9.65%), respectively. Thus, the single-platform method described here allows accurate, rapid and simple measurement of circulating blood myeloid pDC and is suitable for routine enumeration of circulating myeloid pDC.

Simplified Volumetric Flow Cytometry Allows Feasible and Accurate Determination of Cd4 T Lymphocytes in Immunodeficient Patients Worldwide

The determination of CD4 cells is of crucial clinical importance for patients with AIDS. However, the high costs involved represent limitations for CD4 cell counting in developing countries. In order to provide an affordable technique, we introduced a simplified volumetric counting (SVC) technique without sample manipulations and investigated it in a multicentre study. Blood samples from 434 healthy donors and immunodeficient patients were tested in eight hospital laboratories in Europe, Africa and Asia. CD4 cell counts were compared using inhouse flow cytometric methods and the SVC technique. The SVC method was performed on a low-cost flow cytometer (CyFlow SL, Partec, Münster, Germany) after 15 min antibody incubation without pre-analytic manipulations, such as washing or erythrocyte lysing procedures. Linear regression analysis demonstrated a correlation of r=0.942 (Europe), r=0.952 (Africa) and r=0.989 (Asia) between the SVC technique and the in-house methods. Bland Altman plot analysis of all patient data showed a mean bias between the two methods of +26 CD4 cells in favour of the SVC technique (measured range: 6–1905 cells/μl; median CD4 cell count: 388/μl). Three centres used the FACS-count technique (Becton-Dickinson, San José, Calif., USA) as an in-house method dispensing with pre-analytic manipulations. The comparison of SVC and FACS-count method revealed a mean bias of +32 CD4 cells/μl (median CD4 cell count: 349/μl). The accuracy of the SVC was tested on standards with known CD4 cell counts ( n=6) and was shown to be 95.2%. The low-cost device and the simplified no-lyse, no-wash test procedure reduces the costs per determination and facilitates the use of flow cytometry in developing countries.

Validation of the single-platform ISHAGE method for CD34(+) hematopoietic stem and progenitor cell enumeration in an international multicenter study

BACKGROUND

Flow cytometric enumeration of CD34+ hematopoietic sterm and progenitor cells (HPC) is the reference point for undertaking apheresis and evaluation of adequacy for PBSC engraftment. An external quality assurance (EQA) scheme for CD34+ HPC enumeration has been operational in Belgium, Netherlands and Luxemburg (Benelux) since 1995. Within this group, a multicenter survey was held to validate the state-of-the-art methodology, i.e., multiparametric definition of HPC based on light scatter, expression of CD34 and CD45, and counting beads (i.e., 'single platform ISHAGE' method).

METHODS

'Real-time' EQA was used to monitor the application of the single-platform ISHAGE method by 36 participants. Three send-outs of stabilized blood with CD34+ cell counts 35-60 cells/microl were distributed to 36 participants, who were required to assay the samples on three occasions using the standard assay and their local techniques. These results were compared with thosed obtained by 111-116 UK NEQAS participants testing the same specimens.

RESULTS

Using the single platform ISHAGE methods, between-laboratory coefficients of variations (CVs) as low as 10% were achieved. Intra-laboratory CVs were < 5% for approximately 50% of the participants. Local single-platform techniques yielded between-laboratory CVs as low as 9% in both Benelux and UK NEQAS cohorts. In contrast, the lowest between-laboratory CVs using dual-platform techniques were 17% (Benelux) and 21% (UK NEQAS), respectively.

CONCLUSION

The single-platform ISHAGE method for CD34+ cell enumeration has been validated by an international group of 36 laboratories. The observed varation between laboratories allows a meaningful comparison of CD34+ cell enumeration.

Flow rate calibration I: a novel approach for performing absolute cell counts

BACKGROUND

Reports suggest that flow rate (FR) is constant on bench top flow cytometers. Therefore, if FR is constant, the volume acquired in a fixed time period will also be constant, enabling absolute leucocyte counting using flow rate calibration (FRC).

METHODS

FR stability was ascertained on a standard FACSCalibur by counting TruCount beads suspended in phosphate buffered saline over 120 s. Studies using two lysing solutions (FACS lysing solution and PharM Lyse) and corresponding sample lysates established a lysing solution calibration factor (CF). Absolute CD4(+) T-lymphocyte counts on 10 peripheral blood samples determined using FRC were compared with the predicate method TruCount/MultiTEST, incorporating MultiSET software. Linearity studies were also performed at three different flow rates.

RESULTS

A high degree of linearity over a wide range of counts (50 to >1,600 CD4(+) T lymphocytes/microl) at all three pressures was observed. Importantly, there was no significant difference from the predicate method when appropriate lysing solution CF was used.

CONCLUSIONS

Using a simple calibration procedure and incorporation of an appropriate lysing solution CF, we show that FRC can easily be performed. The technical details that underpin this novel approach for absolute leucocyte enumeration are provided.

Flow rate calibration II: a clinical evaluation study using PanLeucoGating as a single-platform protocol

BACKGROUND

CD4(+) T-lymphocyte enumeration is vital for monitoring disease progression in individuals positive for the human immunodeficiency virus (HIV), and as a result, there is a need to develop cost-effective protocols that provide accuracy, precision, and affordability. Recently, PanLeucoGating has been shown to fulfill these requirements; however, although comparable to state-of-the-art single-platform protocols (SP), there is still a requirement for an accurate total white cell count. To overcome this limitation, we recently developed a flow-rate based calibration method that enables the PanLeucoGating protocol to be used as a SP approach, and in this study show that this approach can be used for CD4(+) T-lymphocyte enumeration.

METHODS

A total of 113 HIV samples were analyzed using three protocols: (a) state-of-the art SP bead-based method (MultiSet; predicate protocol), (b) PanLeucoGating protocol used as a dual-platform (DP) approach, and (c) the newly developed flow rate-based SP approach. We demonstrate that flow rate calibration can be achieved easily and that the method is highly comparable to the state-of-the-art SP method.

RESULTS

A high correlation was observed between the predicate protocol and the SP PanLeucoGating approach over the whole range of CD4 counts tested (r(2) = 0.9928; bias 8 cells/microl), including the clinically relevant range (e.g., 0-200 CD4 cells/microl; bias 0 cells/microl). For batched samples, the cost of providing a CD4(+) T-lymphocyte count was reduced to approximately US $1.

CONCLUSIONS

The SP PanLeucoGating is a cost-effective approach to CD4(+) T-lymphocyte enumeration that maintains accuracy and precision.

Crossover study of three methods for low-level white blood cell counting on two types of flow cytometer

BACKGROUND

Flow cytometric methods were previously shown to be preferable to microscopic and volumetric methods for counting residual white blood cells (WBCs). In this study, three flow cytometric, low-level WBC counting methods were cross compared using two flow cytometers.

METHODS

Double-filtered red cell and platelet concentrates were spiked with different amounts of WBC to obtain panels of unspiked and 0.3, 1.0, 3.3, and 10.0 WBC/microl. The methods of BD Biosciences (BDB), Beckman-Coulter (BC), and an in-house method were performed on flow cytometers from BDB and BC. Samples were measured in ninefold. We required that (a) r(2) be at least 0.98 (linearity), (b) at least 80% of observations fell within 20% of expected values (accuracy), and (c) the coefficients of variation be at least 20% (precision) for samples containing at least 3.3 WBC/microl.

RESULTS

For the red cell panel, our requirements were met by the BDB method on both flow cytometers and by the BC and in-house methods on the BDB flow cytometer only. For the platelet panel, our requirements were met on all combinations of methods and flow cytometers, except for the in-house method on the BDB flow cytometer. Intra-assay variation was lowest for the BDB method, irrespective of the type of flow cytometer used.

CONCLUSION

Based on accuracy and precision, the BDB method on the BDB flow cytometer produced the best results for counting low-level WBCs.

Bone marrow transplantation: how important is CD34 cell dose in HLA-identical stem cell transplantation?

A recent analysis of Fred Hutchinson Cancer Research Center data has been undertaken to investigate the association of infused CD34 cell dose with various clinical outcomes after HLA-identical transplantation. Separate assessments for unrelated vs related donors and the use of bone marrow or mobilized G-CSF stimulated peripheral blood mononuclear cells (G-PBMC) have been incorporated. The three primary findings are: (1) Higher CD34 dose results in better neutrophil and platelet recovery in all settings. (2) Higher CD34 doses (8 x 10(6)/kg) are associated with the development of more chronic graft-versus-host disease when using related G-PBMC. (3) Higher CD34 dose is correlated with improved survival after unrelated donor bone marrow transplantation. These data suggest that the CD34 content of a graft can have a significant impact on clinical outcome after allogeneic transplantation, but defining an optimal dose is dependent on both the type of donor and the stem cell source.

HLA-identical stem cell transplantation: is there an optimal CD34 cell dose?

A review of the published literature, supplemented with a recent analysis of Fred Hutchinson data, has been undertaken to investigate the association of infused CD34 cell dose with various clinical outcomes after HLA-identical transplantation. Separate assessments for unrelated vs related donors and the use of bone marrow or mobilized G-PBMC have been incorporated. The three primary findings are: (1) higher CD34 dose results in better neutrophil and platelet recovery in all settings; (2) high CD34 doses (>8 x 10(6)/kg) are associated with the development of more chronic GVHD when using related G-PBMC; (3) higher CD34 dose is correlated with improved survival after bone marrow transplantation, especially with unrelated donors. This is not seen when using G-PBMC. The data suggest that the CD34 content of the graft can have a significant impact on clinical outcome after allogeneic transplantation, but optimal dose is dependent on both donor type and stem cell source.