Reduction of intra- and interlaboratory variation in CD34+ stem cell enumeration using stable test material, standard protocols and targeted training. DK34 Task Force of the European Working Group of Clinical Cell Analysis (EWGCCA)

Combined impact of HLA-allele matching and the CD34-positive cell dose on optimal unit selection for single-unit cord blood transplantation in adults

The combined effects of HLA-allele matching at six-loci (HLA-A, -B, -C, -DRB1, -DQB1, and -DPB1) and CD34⁺ cell dose on clinical outcomes were analyzed in 1,226 adult cases with single-unit unrelated cord blood transplantation. In the six-loci analysis, low HLA-allele matches did not significantly increase the overall mortality compared to higher matches, whereas in the five-loci analysis excluding HLA-DPB1, they caused a higher overall mortality (HR 1.42, p = .002), possibly due to the graft-versus-leukemia effect of HLA-DPB1 mismatches. A lower CD34⁺ cell dose (<.50 × 10⁵/kg) resulted in higher mortality and lower engraftment; these inferior outcomes were offset by high HLA-allele matches (7-10/10 match), while the inferior outcomes of low HLA-allele matches were improved by increasing the CD34⁺ cell dose. Consideration of the combined effects of the CD34⁺ cell dose and HLA matching may expand the options for transplantable units when HLA matching or the CD34⁺ cell dose is inadequate.

The influence of fixation of biological samples on cell count and marker expression stability in flow cytometric analyses

The most common applications of flow cytometry (FC) include diagnostics of haemato-oncological disorders, based on analysis of bone marrow, peripheral blood (PB), or cerebrospinal fluid (CSF) samples. A proper diagnostic process requires standardisation in setting the optimal time frame between material collection and the assay. Unfortunately, this might be difficult to achieve in daily practice due to unintended shipment delays, which might compromise large-scale multicentre studies. Thus, material fixation should be considered as a solution. The most widely used fixative agents are: paraformaldehyde, TransFix^®, Cyto-Chex^®, and serum-containing media. In this review, we attempted to summarise the literature data on the influence of sample storage under different temperatures and times combined with different fixation conditions on the cell count and marker expression levels. Based on the findings of several extensive studies employing fixed PB samples, it can be concluded that the performance of particular fixative greatly depends on the analysed marker and specific PB cell population expressing a given antigen. Preservation of absolute cell count was usually better in Cyto-Chex^®-fixed PB samples, whereas TransFix^® tended to better stabilise marker expression levels. CSF-based studies reveal that both serum-containing media and TransFix^® can prevent cellular loss and enhance FC-based detection of leptomeningeal localisations of haematological malignancies, the latter being more available and having longer shelf-life. As both cell count and marker expression level are the main determinants of quality of biological samples dedicated to FC analyses, it remains to be addressed by the investigators which is the fixative of choice for their specific research aims.

Flow Cytometry Assessment of Bacterial and Yeast Induced Oxidative Burst in Peripheral Blood Phagocytes

Objective: The aim of this study was to verify in our laboratory conditions the performance criteria of a commercial kit (PhagoburstTM, Glycotope Biotechnology) as described by the producers. We have also partially altered the use of the available kit by introducing a non-opsonized Candida albicans stimulus, in addition to the opsonized Escherichia coli stimulus provided by the manufacturer. Material and methods: The peripheral blood samples of 6 clinically healthy adults were tested in triplicate according to the manufacturer recommendations. The intraassay imprecision as well as the ranges of neutrophil and monocyte burst activation triggered by various stimuli were assessed. Results: The activation range of granulocytes and monocytes was similar to the one described by the producer in the presence of E. coli (granulocytes: 78.45-99.43% versus 99.6-99.95%, average %CV of 1.53% versus 0.1%, monocytes: 54.63-92.33% versus 81.80-96.67, average %CV 6.92% versus 1.1%). The leukocyte range of activation in the presence of non-opsonized C. albicans was comparable to the one triggered by the fMLP (N-formyl-methionyl-leucyl-phenylalanine) stimulus. Conclusion: The intra-assay precision obtained in our laboratory conditions, as well as the ranges of activated leukocytes, are comparable to the ones described by the producer when using E. coli as a stimulus. The present study shows that introducing an extra fungal stimulus for burst oxidation assessment could provide additional information regarding the non-specific cellular immune response, particularly in patients at risk for candidemia.

Use of allogeneic apheresis stem cell products as an interlaboratory proficiency challenge

BACKGROUND

AABB Standards requires that laboratories participate in a proficiency test (PT) program for critical analytes. Institutions can purchase commercial PT materials; however, PT can also be performed through interlaboratory exchange. We investigated the utility of allogeneic hematopoietic progenitor cell apheresis (HPC-A) products as an interlaboratory PT challenge for total nucleated cell count (TNC) and CD34 assessment.

STUDY DESIGN AND METHODS

Three-year retrospective and comparative review of unrelated allogeneic HPC-A products received by the University of Michigan between January 2011 and December 2013. Internal TNC and CD34 count were compared to the external collecting facility by paired t test and linear regression. The absolute and percent difference between external and internal counts and 95% limits of agreeability (95% LA) were determined. Results were analyzed relative to donor center location (international, domestic), time zone (domestic), and calendar year.

RESULTS

There was a strong correlation between internal and external TNC, regardless of donor center location or year. For CD34, there was a good correlation between centers (R = 0.88-0.91; slope = 0.95-0.98x) with a median difference of -1% (95% LA, -50%, +47%). This was considerably better than commercial PT challenges, which showed a persistent negative bias for absolute CD34 and CD3 counts.

CONCLUSION

Allogeneic HPC-A products represent an interlaboratory PT exchange for all critical analytes, including TNC and CD34 count, cell viability, and sterility. Allogeneic HPC-A products, which are fresh and transported under validated conditions, are less subject to preanalytical variables that may impact commercial PT samples such as aliquoting and sample homogeneity, commercial additives, and sample stability during manufacturing and transport.

QASI: A collaboration for implementation of an independent quality assessment programme in India

Objective

The HIV pandemic remains a significant global health concern. Accurate determination of CD4+ T-cells in patient samples relies on reliable CD4 enumeration. The Quality Assessment and Standardization programme for Immunological measures relevant to HIV/AIDS (QASI) programme of the Public Health Agency of Canada provides clinical laboratories from resource-limited countries with a mechanism to evaluate the quality of CD4 testing and develop the implementation of an independent national External Quality Assessment (EQA) programme. This study describes how QASI helped develop the capacity for managing a sustainable national CD4 EQA programme in India.

Design

Supported by the Public Health Agency of Canada and Clinton Foundation HIV/AIDS Initiative, QASI engaged with the National AIDS Control Organization and the Indian National AIDS Research Institute to assist in technology transfer in preparation for the implementation/management of an independent CD4 EQA programme. Technology transfer training was provided to support corrective actions and to improve the quality of CD4 testing. Inter-laboratory variation of EQA surveys between pre- and post-skill development was compared.

Results

Prior to training, coefficient of variation values were 14.7% (mid-level CD4 count controls) and 39.0% (low-level). Following training, variation was reduced to 10.3% for mid-level controls and 20.0% for low-level controls.

Conclusion

This training assisted the National AIDS Control Organization and the Indian National AIDS Research Institute in identifying the information necessary for management of an EQA programme, and developed the foundation for India to provide corrective actions for sites with challenges in achieving reliable results for CD4 enumeration. This led to a demonstrable improvement in CD4 testing quality and illustrates how country-specific training significantly improved CD4 enumeration performance for better clinical management of HIV care in India.

Stabilization of Transfected Cells Expressing Low-Incidence Blood Group Antigens: Novel Methods Facilitating Their Use as Reagent-Cells

Background

The identification of erythrocyte antibodies in the serum of patients rely on panels of human red blood cells (RBCs), which coexpress many antigens and are not easily available for low-incidence blood group phenotypes. These problems have been addressed by generating cell lines expressing unique blood group antigens, which may be used as an alternative to human RBCs. However, the use of cell lines implies several drawbacks, like the requirement of cell culture facilities and the high cost of cryopreservation. The application of cell stabilization methods could facilitate their use as reagent cells in clinical laboratories.

Methods

We generated stably-transfected cells expressing low-incidence blood group antigens (Di^a and Lu^a). High-expresser clones were used to assess the effect of TransFix^® treatment and lyophilization as cell preservation methods. Cells were kept at 4°C and cell morphology, membrane permeability and antigenic properties were evaluated at several time-points after treatment.

Results

TransFix^® addition to cell suspensions allows cell stabilization and proper antigen detection for at least 120 days, despite an increase in membrane permeability and a reduction in antigen expression levels. Lyophilized cells showed minor morphological changes and antigen expression levels were rather conserved at days 1, 15 and 120, indicating a high stability of the freeze-dried product. These stabilized cells have been proved to react specifically with human sera containing alloantibodies.

Conclusions

Both stabilization methods allow long-term preservation of the transfected cells antigenic properties and may facilitate their distribution and use as reagent-cells expressing low-incidence antigens, overcoming the limited availability of such rare RBCs.

Multi-site evaluation of the BD Stem Cell Enumeration Kit for CD34(+) cell enumeration on the BD FACSCanto II and BD FACSCalibur flow cytometers

BACKGROUND AIMS

Evaluation of the BD Stem Cell Enumeration Kit was conducted at four clinical sites with flow cytometry CD34(+) enumeration to assess agreement between two investigational methods: (i) the BD FACSCanto II and BD FACSCalibur systems and (ii) the predicate method (Beckman Coulter StemKit and StemTrol, Immunotech SAS, Beckman Coulter, Marseille Cedex 9, France).

METHODS

Leftover and delinked specimens (n = 1032) from clinical flow cytometry testing were analyzed on the BD FACSCanto II (n = 918) and BD FACSCalibur (n = 905) in normal and mobilized blood, frozen and thawed bone marrow and leucopheresis and cord blood anticoagulated with citrate phosphate dextrose, anticoagulant citrate dextrose-solution A, heparin and ethylenediaminetetraacetate, alone or in combination. Fresh leucopheresis analysis addressed site equivalency for sample preparation, testing and analysis.

RESULTS

The mean relative bias showed agreement within predefined parameters for the BD FACSCanto II (-2.81 to 4.31 ±7.1) and BD FACSCalibur (-2.69 to 5.2 ±7.9). Results are reported as absolute and relative differences compared with the predicate for viable CD34(+), percentage of CD34(+) in CD45(+) and viable CD45(+) populations (or gates). Bias analyses of the distribution of the predicate low, mid and high bin values were done using BD FACSCanto II optimal gating and BD FACSCalibur manual gating for viable CD34(+), percentage of CD34(+) in CD45(+) and viable CD45(+). Bias results from both investigational methods show agreement. Deming regression analyses showed a linear relationship with R(2) > 0.92 for both investigational methods.

DISCUSSION

In conclusion, the results from both investigational methods demonstrated agreement and equivalence with the predicate method for enumeration of absolute viable CD34(+), percentage of viable CD34(+) in CD45(+) and absolute viable CD45(+) populations.

Standardizing leucocyte PNH clone detection: an international study

BACKGROUND

Consensus and Practical Guidelines for robust high-sensitivity detection of glycophosphatidylinostitol-deficient structures on red blood cells and white blood cells in paroxysmal nocturnal hemoglobinuria (PNH) were recently published.

METHODS

UK NEQAS LI issued three stabilized samples manufactured to contain no PNH cells (normal), approximately 0.1% and 8% PNH leucocyte populations, together with instrument-specific Standard Operating Procedures (SOPs) and pretitered antibody cocktails to 19 international laboratories experienced in PNH testing. Samples were tested using both standardized protocol/reagents and in-house protocols. Additionally, samples were issued to all participants in the full PNH External Quality Assessment (EQA) programs.

RESULTS

Expert laboratory results showed no difference in PNH clone detection rates when using standardized and their "in-house" methods, though lower variation around the median was found for the standardized approach compared to in-house methods. Neutrophil analysis of the sample containing an 8% PNH population, for example, showed an interquartile range of 0.48% with the standardized approach compared with 1.29% for in-house methods. Results from the full EQA group showed the greatest variation with an interquartile range of 1.7% and this was demonstrated to be significantly different (P<0.001) to the standardized cohort.

CONCLUSIONS

The results not only demonstrate that stabilized whole PNH blood samples are suitable for use with currently recommended high-sensitivity reagent cocktails/protocols but also highlight the importance of using carefully selected conjugates alongside the standardized protocols. While much more variation was seen among the full UK NEQAS LI EQA group, the standardized approach lead to reduced variation around the median even for the experienced laboratories.

CD34⁺ cell content in unrelated allogeneic peripheral blood stem cell grafts transported internationally. Does the inter-laboratory variability affect comparability of graft quality data?

BACKGROUND

Increasing numbers of unrelated hematopoietic stem cell grafts are transported internationally and evaluated concurrently in different laboratories. The graft quality assessment using the CD34(+) enumeration could be influenced by inter-laboratory variability.

METHODS

We retrospectively analyzed the content of CD34(+) cells in 154 consecutive collections being performed in different transplant centers during two periods (2003-2004, 2007-2010). All samples were tested twice in our own and partner laboratories. CD34(+) percentage and absolute number were compared.

RESULTS

The percentage and the total CD34(+) content correlated well in both observed periods (CD34(+)%: r=0.899 and r=0.922; CD34(+)×10(8)/kg: r=0.966 and r=0.880; p<0.0001). Median CD34(+) percentages obtained in our centre in comparison with other laboratories were 0.54% vs. 0.46% in 2003-2004 and 0.69% vs. 0.70% in 2007-2010 period. The degree of laboratory compliance was affected by the laboratory identity. CD34(+) percentage reported by one laboratory and CD34(+)×10(8)/kg reported by three from twelve laboratories lacked statistically significant correlation with our own data.

CONCLUSIONS

The study documented that results of CD34(+) cell dose assessment of the same grafts reported by different transplant centers are comparable. The graft quality data and the CD34(+) enumeration possess a limited level of inter-laboratory variability.

Direct volumetric flow cytometric quantitation of CD34+ stem and progenitor cells

OBJECTIVES

In this study, we compared a classic single-platform (SP) method applying beads for enumeration of CD45+ or CD34+ cells with a new device allowing direct volumetric measurements of stem and progenitor cells.

BACKGROUND

Following apheresis and cyropreservation, the precise enumeration of CD34+ cells as key parameter of graft quality is mandatory for the clinical course after transplantation. Currently, flow cytometry with SP technique represents the 'gold standard' for such determinations.

METHODS/MATERIALS

Fresh samples, 14 from mobilised peripheral blood (PB), 9 from apheresis products (AP) and 13 samples from frozen-thawed (FT) haematopoietic progenitor cell grafts, were analysed for CD34+ cells, CD45+ cells, and in frozen-thawed samples for viability by a bead-based flow cytometric method and in parallel by a direct, volumetric flow cytometric method.

RESULTS

Comparison of CD34+ analyses revealed a significant correlation (P < 0·01) for each material between both techniques with r = 0·95 (PB), r = 0·933 (AP) and r = 0·929 (FT). Also, for analysis of CD45+ cells µL(-1) , the measured numbers evaluated with the different techniques did not significantly differ for all three materials analysed. In frozen-thawed samples, the analysis of viability was comparable for both techniques.

CONCLUSIONS

The results of this study demonstrate that a direct volumetric analysis of CD34+ cells µL(-1) or CD45+ cells µL(-1) is feasible. This technique represents a simple and economical approach for standardisation of progenitor and stem cell analyses.

VERITAS?: A time for VERIQAS™ and a new approach to training, education, and the quality assessment of CD4+ T lymphocyte counting (I)

BACKGROUND

The aim of clinical laboratories is to produce accurate and reproducible results to enable effective and reliable clinical practice and patient management. The standard approach is to use both internal quality control (IQC) and external quality assessment (EQA). IQC serves, in many instances, as a "go, no go" tool to provide real time assurance that instruments and reagent or test systems are performing within defined specifications. EQA however, takes a snapshot at a specific point in time of the full testing process, results are compared to other laboratories performing similar testing but inevitably has some built in delay from sample issue to performance data review. In addition, if IQC or EQA identify areas of concern it can be difficult to determine the exact nature of the problem. In an attempt to address this problem, we have developed an instant QA panel that we have termed VERIQAS™, specifically for CD4(+) T lymphocyte counting, and have undertaken a "proof of principle" pilot study to examine how the use of VERIQAS™ could result in improvement of laboratory performance. In addition, we have examined how this approach could be used as a training and education tool (in a domestic/international setting) and potentially be of value in instrument validation/switch studies (a switch study being defined as a laboratory changing from one method/instrument to a new method/instrument with the VERIQAS™ panel being used as an adjunct to their standard switch study protocol).

METHODS

The basic panel consists of 20 stabilized samples, with predefined CD4(+) T lymphocyte counts, that span low clinically relevant to normal counts, including some blinded replicates (singlet up to quadruplicate combinations). The CD4(+) T lymphocyte target values for each specimen is defined as the trimmed mean ± 2 trimmed standard deviations, where the trimmed values are derived from the CD4(+) T lymphocyte counts reported by the participating centers (~780 laboratories) that receive each UK NEQAS for Leucocyte Immunophenotyping send out. Results for the VERIQAS™ panel were returned online, via a specially designed website, and the participant was provided with an immediate assessment (pass or fail).

RESULTS

To date, the panel has been preliminary trialed by eight laboratories to (i) assess pre-EQA qualification (two laboratories); (ii) address performance issues (two laboratories); or (iii) validate new instruments or techniques (four laboratories). Interestingly, even in this pilot study, the panel has been instrumental in identifying specific technical problems in laboratories with EQA performance issues as well as confirming that implementation of new techniques or instruments have been successful.

CONCLUSION

We report here a new and novel "proof of principle" pilot study to quality assessment, that we have termed VERIQAS™, designed to provide instant feedback on performance. Participating laboratories receive 20 "blinded" samples that are in singlet up to quadruplicate combinations. Once a centre reports its results via a website, immediate feedback is provided to both the participant and the EQA organizers, enabling, if required, the initiation of targeted remedial action. We have also shown that this approach has the potential to be used as a tool for prequalification, troubleshooting, training and instrument verification. Pilot phase field trials with VERIQAS™ have shown that the panel can highlight laboratory performance problems, such as suboptimal instrument set up, pipetting and gating strategies, in a rapid and efficient manner. VERIQAS™ will now be introduced, where appropriate, as a second phase study within UK NEQAS for Leucocyte Immunophenotyping to assist those laboratories that have performance issues and also made available to laboratories for training and education of staff and instrument validation studies.

ISHAGE protocol: are we doing it correctly?

BACKGROUND

Flow cytometric CD34(+) stem cell enumeration is routinely performed to optimize timing of peripheral blood stem cell collections and assess engraftment capability of the apheresis product. While a number of different flow methodologies have been described, the highly standardized ISHAGE protocol is currently the most widely employed, with 204/255 (81%) international participants in the UK NEQAS CD34(+) stem cell enumeration program indicating their use of this method. Recently, two laboratories were identified as persistent poor performers, a fact attributed to incorrect ISHAGE protocol usage/setup. This prompted UK NEQAS to question whether other laboratories were making similar errors and, if so, how this might affect individual EQA performance.

METHODS AND RESULTS

In send out 0801, where two stabilized samples were issued, the EQA center surveyed 255 participants with flow analysis data and subsequent results collected. One hundred and ninety-six laboratories returned results with 103 returning dot plots. Eighty-three out of one hundred and three stated that they used the ISHAGE protocol gating strategy but 43% (36/83) were incorrectly set-up. Analysis of the data showed those incorrectly using single platform ISHAGE gating strategy were twice as likely to fail an EQA exercise compared to those using the protocol correctly. This failure rate increased two fold when incorrect ISHAGE protocol was used in a dual platform setting.

CONCLUSION

This study suggests a widespread fundamental lack of understanding of the ISHAGE protocol and the need to deploy it correctly, potentially having significant clinical implications and highlights the need to monitor participants rigorously in their deployment of the ISHAGE protocol. It is hoped that once these findings have been disseminated, performance can be improved.

Basal levels of CD34 positive cells in peripheral blood differ between individuals and are stable for 18 months

BACKGROUND

Detection of basal levels of CD34 progenitor cells is a rare event analysis enumerating cells down to 1 cell/μl. A reproducible analytic approach was used in three independent clinical trials in which multiple sequential assays were obtained from the same individual.

METHODS

A 4 color panel combining, HLA-DR, CD34, CD45, and CD11b was used in a dual platform analysis to quantify CD34 progenitor cells in peripheral blood, with quality control focused at the lowest measurements (i.e., basal levels), where assay error is greatest.

RESULTS

Repeat testing of individuals every 4 h over the course of 6 days provided a unique opportunity to assess the precision of the analytic technique and identified basal differences between individuals. In a second study, the basal levels were stable for 10 weeks while in a third study the individual differences were maintained for 18 months. This approach was then used to monitor the kinetics of mobilization of CD34 cells following G-CSF stimulation every 4 h.

CONCLUSIONS

The differences between individuals in basal levels of CD34 were shown to be a biologic constant, stable for 18 months and not a result of the variability of the assay, shown by low coefficients of variation for each individual. These results can be used to augment a quality control program by monitoring individuals over time to establish intra and inter-laboratory assay precision. In addition, the response of six individuals to G-CSF demonstrated differences in absolute numbers of mobilized CD34 progenitor cells but showed identical kinetics, peaking at 80-110 h.

CD34+ Cell Enumeration by Flow Cytometry: A Comparison of Systems and Methodologies

Context.—An increasing number of medical centers can collect bone marrow, peripheral blood, or umbilical cord stem cells. Pathology laboratories should accommodate this trend, but investment in additional equipment may be impractical.

Objectives.—To compare CD34+ cell counting results by using 2 widely available flow cytometry systems, with and without the use of a separate hematology analyzer (ie, single-platform versus dual-platform methodologies).

Design.—Whole blood and peripheral blood stem cell (PBSC) samples were analyzed from 13 healthy allogeneic PBSC donors and 46 autologous PBSC donors with various malignancies. The Cytomics FC500 (Beckman Coulter, Fullerton, California) was compared with the FACSCalibur (BD Biosciences, San Jose, California). Dual-platform CD34+ cell counting incorporated data from a KX-21 hematology analyzer (Sysmex, Kobe, Japan).

Results.—Subtle differences in CD34+ cell counting between 2 systems and 2 methods did not achieve statistical significance.

Conclusion.—Different systems and methods for CD34+ cell enumeration, properly validated, can support care for patients undergoing transplants and provide meaningful data for multicenter studies or meta-analyses.

Interlaboratory variability of CD34+ stem cell enumeration. A pilot study to national external quality assessment within the Czech Republic

We present the results of a pilot study concerning the interlaboratory variability of CD34+ enumeration. Three surveys, each including a set of samples, were sent to participating Czech flow cytometry laboratories. The efficacy of this exercise was determined by the reduction in interlaboratory variation and the influence of method used on assay outcome. The variability in results of CD34+ enumeration declined with time. The mean coefficient of variation (CV) of measurement among laboratories dropped, from 58% in first survey to 32% in last survey. All tested variables (gating strategy, platform methodology, sample preparation) affected the variability of the assay. Sample preparation method was associated with a significant bias of absolute CD34+ cell counts. Initially, the outcome of the measurement was also affected by the participating laboratory (identified by a unique laboratory number; ULN). However, laboratories with poorer performance modified their protocols during the study, and the ULN ceased to influence the variability. This study was successful in reducing the interinstitutional variability of CD34+ enumeration. It was shown that the implementation of a standardized protocol does not guarantee accurate measurement. Our research design represents a useful tool, which allows verification of the proper use of a standardized method, the training of operators and feedback in response to the survey results.

External quality assurance of circulating tumor cell enumeration using the CellSearch(®) system: a feasibility study

BACKGROUND

Circulating tumor cells (CTCs) are cells that have detached from solid tumors and entered the blood. CTCs can be detected, among others, by semi-automated immunomagnetic enrichment and image cytometry using CellSearch® (Veridex, Raritan, NJ). We studied the feasibility of external quality assurance (EQA) of the entire CellSearch procedure from blood draw to interpretation of results in multiple laboratories.

METHODS

Blood samples from six cancer patients and controls were distributed to 14 independent laboratories to test between-laboratory, between-assay, and between-instrument variation. Additionally, between-operator variability was assessed through the interpretation of blinded images of all blood samples on a website.

RESULTS

Shipment and storage of samples had no influence on CTC values. Between-instrument (coefficient of variation (CV) < 12%) and between-assay variation was low (CV ≤ 20%), indicating high reproducibility. However, between-laboratory CV ranged from 45 to 64%. Although inter-operator agreement on image interpretation (Fleiss' κ statistics) ranged from "substantial" to "almost perfect," image interpretation, particularly of samples containing high numbers of apoptotic cells, was the main contributor to between-laboratory variation.

CONCLUSIONS

This multicenter study shows the feasibility of an EQA program for CTC detection in patient samples, and the importance of continuation of such a program for the harmonization of CTC enumeration.

Higher incidence of relapse in patients with acute myelocytic leukemia infused with higher doses of CD34+ cells from leukapheresis products autografted during the first remission

The stem cell source for autologous transplantation has shifted from bone marrow to peripheral blood (PB). We previously showed that relapse incidence in patients with acute myelocytic leukemia autografted in first remission (CR1) was greater with PB than bone marrow, and a poorer outcome was associated with a shorter CR1 to PB transplantation interval (≤ 80 days). Leukemic and normal progenitors are CD34(+) and can be concomitantly mobilized; we assessed whether an association exists between the infused CD34(+) cell dose and outcome. The infused CD34(+) cell doses were available for 772 patients autografted more than 80 days after CR1 and were categorized by percentiles. We selected the highest quintile (> 7.16 × 10(6)/kg) as the cutoff point. By multivariate analysis, relapse was more probable in patients who received the highest dose (hazard ratio = 1.48; 95% confidence interval, 1.12-1.95; P = .005), and leukemia-free survival was worse (hazard ratio = 0.72; 95% confidence interval, 0.55-0.93; P = .01). In conclusion, in patients autografted in first remission, relapse was higher and leukemia-free survival lower for those who received the highest CD34(+) PB doses.

Exercise training and endothelial progenitor cells in haemodialysis patients

Haemodialysis patients have few endothelial progenitor cells (EPCs) and an unfavourable cardiovascular outcome. The effects on peripheral blood CD34(+) cells and EPCs of a 6-month walking exercise programme were studied. Thirty dialysis patients (20 males, age 67 +/- 12 years) were prescribed exercise (two daily 10-min home walking sessions at moderate intensity, group E, n = 16) or not prescribed exercise (control, group C, n = 14). On entry and after 6 months peripheral blood CD34(+) cells, EPCs (assessed as CD34(+) cells co-expressing AC133 and vascular endothelial growth factor receptor 2 [VEGFR2], and as endothelial colony-forming units [e-CFU]) and exercise capacity (6-min walking distance, 6MWD) were evaluated. In group E, 6MWD and e-CFU increased significantly during the study period, with no significant changes in CD34(+) or CD34(+) AC133(+) VEGFR2(+) cell numbers. The change in e-CFU was directly and significantly correlated to patient-reported training load. Group C showed no significant change in any variable. In haemodialysis patients, moderate-intensity exercise selectively increased the number of e-CFU.

Consistency of the initial cell acquisition procedure is critical to the standardization of CD34+ cell enumeration by flow cytometry: results of a pairwise analysis of umbilical cord blood units and cryopreserved aliquots

BACKGROUND

The CD34+ cell content is a predictive factor for engraftment and survival after umbilical cord blood (UCB) transplantation. The high variability in the CD34 assay results in different recommended cell doses for infusion across transplant centers and also limits the clinical utility of the CD34+ cell counts provided by cord blood banks (CBBs). This bi-institutional study was intended to understand the sources of this variability.

STUDY DESIGN AND METHODS

The level of CD34 agreement between the University of Minnesota (UM) and the Madrid CBB (MCBB) was evaluated on 50 UCB units before and after cryopreservation. Two cryopreserved vials per unit were thawed and processed at both laboratories. Dual-platform ISHAGE-based flow cytometry was used for CD34 enumeration.

RESULTS

Postthaw nucleated cell recoveries were similar. However, whereas CD34+ cell enumeration before freezing was 0.35 +/- 0.22 percent, the results after thawing were 0.98 +/- 0.65 and 0.57 +/- 0.39 percent at UM and MCBB, respectively. Bland-Altman plots analysis ruled out the interchangeability of MCBB and UM CD34 values. Differences in the initial cell acquisition settings accounted for most of the CD34 discrepancy, which was no longer present after normalization of the forward scatter threshold for cell acquisition.

CONCLUSIONS

The standardization of CD34+ cell enumeration by flow cytometry is strongly reliant on a consistent initial cell acquisition procedure. The interlaboratory variation can be minimized by using frozen cell aliquots as reference samples. Both requisites should be considered for CD34 testing and UCB unit selection by regulatory institutions involved with cord blood banking and transplantation.

Analytical performance of a standardized single-platform MHC tetramer assay for the identification and enumeration of CMV-specific CD8+ T lymphocytes

Major histocompatibility complex (MHC) multimers that identify antigen-specific T cells, coupled with flow cytometry, have made a major impact on immunological research. HLA Class I multimers detect T cells directed against viral, tumor, and transplantation antigens with exquisite sensitivity. This technique has become an important standard for the quantification of a T cell immune response. The utility of this method in multicenter studies, however, is dependant on reproducibility between laboratories. As part of a clinical study using a standardized two-tube three-color single-platform method, we monitored and characterized performance across multiple sites using tetramers against the T cell receptors (TCR) specific for MHC Class I, A*0101--VTEHDTLLY, A*0201--NLVPMVATV and B*0702--TPRVTGGGAM CMV peptides. We studied the analytical performance of this method, focusing on reducing background, maximizing signal intensity, and ensuring that sufficient cells are enumerated to provide meaningful statistics. Inter and intra-assay performance were assessed, which included inherent variability introduced by shipping, type of flow cytometer used, protocol adherence, and analytical interpretation across a range of multiple sample levels and specificities under routine laboratory testing conditions. Using the described protocol, it is possible to obtain intra- and interlab CV's of <20%, with a functional sensitivity for absolute tetramer counts of 1 cell/microL and 0.2% tetramer+ percent for A*0101, A*0201, and B*0702 alleles. The standardized single-platform MHC tetramer assay is simple, rapid, reproducible, and useful for assessing CMV-specific T cells, and will allow for reasonable comparisons of clinical evaluations across multiple centers at clinically relevant thresholds (2.0-10.0 cells/microL).

CD4 immunophenotyping in HIV infection

The ability to rapidly identify immune cell subsets such as CD4 cells, which became possible around the same time as the onset of the HIV/AIDS pandemic, was one of the greatest advances in clinical and diagnostic immunology. The evolution of this global pandemic and the subsequent development of treatment strategies to prolong the life of infected individuals mean that it is now more crucial than ever that we develop affordable, reliable and accurate methods for the enumeration of CD4 cells. Here, we provide an overview of the historical developments in CD4 enumeration technologies that are related to HIV infection, and summarize the current technological challenges that must be overcome to meet the needs of those living with HIV infection.

The Role of Flow Cytometry in the Diagnosis of Paroxysmal Nocturnal Hemoglobinuria in the Clinical Laboratory

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired hematopoietic stem cell disorder closely related to aplastic anemia. Hemolytic anemia and life-threatening thromboses are common features in many patients. Rapid diagnosis is highly desirable and flow cytometry plays a key role in the laboratory investigation of PNH. By demonstrating absence of cell membrane glycosylphosphatidylinositol-anchored proteins from granulocytes or red cells, a definitive diagnosis of PNH can be established. This can have a considerable impact on patient management and outcome. As with all rare diseases, internal and external quality assurance is essential for good laboratory practice and to fulfill the requirements of national laboratory accreditation schemes.

Flow cytometric CD34+ stem cell enumeration: lessons from nine years' external quality assessment within the Benelux countries

BACKGROUND

A biannual external quality assurance (EQA) scheme for flow cytometric CD34+ haematopoietic stem cell enumeration has been operational in the Benelux countries since 1996. In an evaluation of the results of 16 send-outs, we studied the effects of the methods used on assay outcome and whether or not this exercise was effective in reducing between-laboratory variation.

METHODS

Data were analyzed using robust multivariate regression. This approach is relatively insensitive to outliers and is used to assess the effect of methodological aspects of CD34+ cell counting on the bias and variability.

RESULTS

Five variables were associated with significant bias of absolute CD34+ cell counts: (i) unique laboratory number (ULN), (ii) gating strategy; (iii) CD34 mAb fluorochrome; (iv) type of flow cytometer, and (v) method of sample preparation. In addition, ULN and platform methodology (i.e., single vs. dual) contributed significantly to the variability of this assay. Overall, the variability in results of CD34+ cell enumeration has declined with time; in particular, after a practical workshop in which participants were trained to use the "single platform ISHAGE protocol."

CONCLUSIONS

Between-laboratory variation in CD34+ cell enumeration can be reduced by standardization of methodologies between centres. Our approach, i.e., EQA with targeted training and feedback in response to reported results, has been successful in reducing the variability of CD34+ cell enumeration between participants.

Twenty years of external quality assurance in clinical cell analysis--a tribute to Jean-Luc D'Hautcourt

External quality assurance (EQA) programs in clinical cell analysis are now a consolidated item of laboratory practice. All the flow cytometric testings with an impact on clinical decision making have been submitted to regular EQA programs during the last 20 years, and this has produced internationally homogeneous guidelines, with a remarkable improvement in result reproducibility.Jean-Luc D'Hautcourt was a pioneer in this field, and his valuable contributions to flow cytometric method standardization and to the dissemination of the educational aspects of EQA programs are recognized. The different methodological approaches undertaken in the United States and Europe are discussed. The educational role of SIHON in the Benelux Countries and of UKNEQAS for Leucocyte Immunophenotyping worldwide is emphasized. Accredited and accreditating EQA programs require an impressive degree of organization and technical knowledge, so that only major international providers can afford such a task nowadays. However, small local studies still provide the necessary stimulus to the continuous improvement of the scientifical aspects of EQA schemes.

Mobilization of endothelial progenitor cells in patients with hematological malignancies after treatment with filgrastim and chemotherapy for autologous transplantation

In recent years, endothelial progenitor cells (EPCs), gave rise to increasing interest because of their possible use as a therapeutic tool in the treatment of vascular lesions in ischemic tissues or as a target for anti neoplastic therapy. It has been shown that several drugs can increase the number of EPCs into the peripheral blood (PB). However, there is insufficient data concerning the mobilization and collection of EPCs during CD34+ cell mobilization. In this study, we have evaluated EPC mobilization and collection in a series of 47 patients affected by lymphoid neoplasms [31 non Hodgkin lymphoma and 16 multiple myeloma] undergoing CD34+ cell mobilization with cyclophosphamide (4000 mg/m2) and Filgrastim (5 microg/kg). PB EPCs identified by flow cytometry as CD34+/VEGFR2+/CD133+ cells showed a peak on day +10. This peak paralleled that of PB CD34+/CD45+ cells. A direct correlation was observed between CD34+ and CD34+/VEGFR2+/CD133+ cells (r = 0.99 P < 0.0001). An average of 23.7 x 10e6 CD34+/VEGFR2+ CD133+ cells have been collected (range 12.1-41.76 x 10e6). These findings showed that in hematological diseases, cyclophosphamide in combination with filgrastim allows the mobilization and collection of large numbers of EPCs which may be used for reparative medicine studies in these patients.

A single bolus of a long-acting erythropoietin analogue darbepoetin alfa in patients with acute myocardial infarction: a randomized feasibility and safety study

AIMS

Besides stimulating hematopoiesis, erythropoietin (EPO) protects against experimental ischemic injury in the heart. The present study evaluated the safety and tolerability of EPO treatment in non-anemic patients with acute myocardial infarction (MI).

METHODS AND RESULTS

In this single-center, investigator-initiated, prospective study, patients with a first acute MI were randomized to one bolus of 300 microg darbepoetin alfa or no additional medication before primary coronary intervention. Twenty-two patients (mean age 59 +/- 2 years) were included. In the darbepoetin group, serum EPO-levels increased to 130-270 times that of controls, within the first 24 h. After darbepoetin administration, only small and non-significant changes in hematocrit levels were observed, while endothelial progenitor cells (EPCs, CD34+/CD45-) were increased at 72 h (2.8 vs. 1.0 cells/microl in control group, p < 0.01). No adverse events were recorded during the 30-day follow-up. After 4 months, left ventricular ejection fraction was similar in the two groups (52 +/- 3% in darbepoetin vs. 48 +/- 5% in control group, p = NS).

CONCLUSIONS

Intravenous single high-dose darbepoetin alfa in acute MI is both safe and well tolerated. Darbepoetin treatment after MI stimulates EPCs mobilization. The results of this first pilot study support a larger scale clinical trial to establish efficacy of EPO administration in patients after acute MI.

Normal lymphocytes from leukemic samples as an internal quality control for fluorescence intensity in immunophenotyping of acute leukemias

BACKGROUND

Multiparametric flow cytometry has become an indispensable but complex tool for the diagnosis of acute leukemias. Interpretation of immunophenotypic data within a six-parameter analytical space relies on the standardization and validation of the instrument, the reagents, and the procedure. To address whether or not residual normal lymphocytes, usually present within leukemic samples, can serve as internal quality control for fluorescence intensity, 116 leukemic and 35 normal samples were analyzed.

METHODS

Eight laboratories participated in the study and recruited a total of 151 individuals including 29 patients with B-cell precursor acute lymphoblastic leukemia (BCP-ALL), 77 with acute myeloid leukemia (AML), 10 with T-cell precursor acute lymphoblastic leukemia (T-ALL), and 35 normal bone marrow donors. Lymphocytes were gated according to the CD45hi/SSClo gating strategy, after which median fluorescence intensities (MFI) as well as percentages of positive cells (%positive) for CD19, CD22, CD7, and CD3 were recorded. Nonparametric statistics were used to compare variation within and between laboratories.

RESULTS

Normal lymphocytes within leukemic samples do not show substantial differences compared to lymphocytes from normal controls with respect to expression of CD19, CD22, CD7, and CD3. In particular, longitudinal control charts of MFI values for CD3 antigen provide useful information on analytical and instrument performance.

CONCLUSION

Residual normal lymphocytes can serve as internal quality control for studies addressing fluorescence intensity in the setting of immunophenotyping of acute leukemias.

Interleukin-8 is associated with circulating CD133+ progenitor cells in acute myocardial infarction

AIMS

Release of progenitor cells is observed during inflammatory conditions and contributes to neovascularization. We, therefore, sought to investigate the relationship of circulating progenitor cells and interleukin (IL)-8 in acute myocardial infarction (AMI).

METHODS AND RESULTS

From patients with stable angina and AMI, serial venous blood samples were obtained. The number of circulating CD133+CD45- progenitor cells, endothelial progenitor cells (EPCs), and circulating endothelial P1H12+CD45- cells was analyzed by flow cytometry. After stenting in patients with AMI, an increase in plasma IL-8 and vascular endothelial growth factor (VEGF) concentrations was observed, which was only minimal in patients with stable angina. Only in patients with AMI, this was followed by an increase in circulating CD133+CD45- progenitor cells. In contrast, circulating endothelial P1H12+CD45- cells and E-selectin RNA expression in peripheral blood were only elevated early in AMI, indicating shedding of activated endothelial cells. Multivariable analysis revealed an association of IL-8 and circulating CD133+CD45- progenitor cells in AMI, in addition to statin therapy and risk factor profile.

CONCLUSION

In AMI, IL-8 is associated with circulating progenitor cells. In addition to the pro-angiogenic functions of IL-8 and VEGF, this mechanism may contribute to new vessel generation and, thereby, improve myocardial function.

Use of granulocyte-colony stimulating factor during acute myocardial infarction to enhance bone marrow stem cell mobilization in humans: clinical and angiographic safety profile

AIMS

There is increasing evidence that stem cell (SC) mobilization to the heart and their differentiation into cardiac cells is a naturally occurring process. We sought to assess the safety and feasibility of granulocyte-colony stimulating factor (G-CSF) administration in humans to enhance SC mobilization and left ventricle (LV) injury repair during myocardial infarction (MI).

METHODS AND RESULTS

Twenty patients with STEMI (mean age, 61+/-10 years), of whom 14 were submitted to primary percutaneous coronary intervention, were randomized to G-CSF (5 microg/kg/day s.c. for 4 consecutive days) or placebo. At entry and then at months 3 and 6, (99m)Tc-sestamibi gated-SPECT was performed to estimate extension of perfusion defect (PD) and LV function. The study drug was well tolerated and induced a significant increase of white blood count, CD34(+) cells, and CD34(+) cells coexpressing AC133 and VEGFR-2. At follow-up, treated and placebo groups did not differ for the angiographic coronary late loss and showed a similar pattern of PD recovery, whereas in the former at 6 months LVEF and especially LVEDV tended to be relatively higher (P=0.068) and lower (P=0.054), respectively.

CONCLUSION

G-CSF administration in acute MI patients was feasible and did not lead to any clinical or angiographic adverse events and resulted in CD34(+) and CD34(+)AC133(+)VEGFR2(+) cell mobilization.

Enumeration of antigen-specific CD8+ T lymphocytes by single-platform, HLA tetramer-based flow cytometry: a European multicenter evaluation

BACKGROUND

HLA class I peptide tetramers represent powerful diagnostic tools for detection and monitoring of antigen-specific CD8(+) T cells. The impetus for the current multicenter study is the critical need to standardize tetramer flow cytometry if it is to be implemented as a routine diagnostic assay. Hence, the European Working Group on Clinical Cell Analysis set out to develop and evaluate a single-platform tetramer-based method that used cytomegalovirus (CMV) as the antigenic model.

METHODS

Absolute numbers of CMV-specific CD8(+) T cells were obtained by combining the percentage of tetramer-binding cells with the absolute CD8(+) T-cell count. Six send-outs of stabilized blood from healthy individuals or CMV-carrying donors with CMV-specific CD8(+) T-cell counts of 3 to 10 cells/microl were distributed to 7 to 16 clinical sites. These sites were requested to enumerate CD8(+) T cells and, in the case of CMV-positive donors, CMV-specific subsets on three separate occasions using the standard method.

RESULTS

Between-site coefficients of variation of less than 10% (absolute CD8(+) T-cell counts) and approximately 30% (percentage and absolute numbers of CMV-specific CD8(+) T cells) were achieved. Within-site coefficients of variation were approximately 5% (absolute CD8(+) T-cell counts), approximately 9% (percentage CMV-specific CD8(+) T cells), and approximately 17% (absolute CMV-specific CD8(+) T-cell counts). The degree of variation tended to correlate inversely with the proportion of CMV-specific CD8(+) T-cell subsets.

CONCLUSIONS

The single-platform MHC tetramer-based method for antigen-specific CD8(+) T-cell counting has been evaluated by a European group of laboratories and can be considered a reproducible assay for routine enumeration of antigen-specific CD8(+) T cells.

Evaluation of leukocyte stabilisation in TransFix®-treated blood samples by flow cytometry and transmission electron microscopy

In this report, we have evaluated the effects of a TransFix-based stabilisation technique on leukocyte scatter characteristics, immunophenotyping, membrane permeability, absolute cell counting and morphology to extend previously reported flow cytometric data focused on the lymphocyte population. We show that scatter characteristics, immunophenotyping and absolute cell counting are well preserved, particularly in the lymphocyte population. Nevertheless, a general increase in membrane permeability, evaluated by propidium iodide (PI) uptake, was observed in TransFix-treated leukocyte subsets. Ultrastructural observations show selective morphological preservation (up to 10 days of storage) of lymphocytes and, to a lesser extent, of monocytes. In contrast, granulocytes have necrosis-like features, although the plasma membrane seems well preserved. Therefore, electron microscopy observations reflect modifications induced in different cell populations as evidenced by flow cytometry (FC). The data indicate that this short-term stabilisation method is particularly suitable for the analysis of human lymphocytes and it is a good procedure for quality control programmes for inter- and intra-laboratory performance evaluation; good results are obtained with respect to antigen definition and absolute cell counting procedures. Any apoptotic pathways in leukocyte subsets are blocked for at least 10 days.

Impact of CD34 subsets on engraftment kinetics in allogeneic peripheral blood stem cell transplantation

Our objective was to evaluate, probably for the first time, the impact of CD34 subsets on engraftment kinetics in allogeneic PBSC transplantation (PBSCT). PBSC graft components were analyzed in 62 cases for the absolute count/kg of total CD34+ and the following subsets: DR- and +, CD71+/-, CD38+/-, CD33+/- and CD61+/-. Time to ANC >0.5 and >1 x 10(9)/l and platelets >20 and >50 x 10(9)/l was reported. The median value for each parameter was used to discriminate rapid from slow engraftment. Four parameters showed significant predictive power of early neutrophil engraftment, namely CD34+ /DR- (P = 0.002), CD34+/38- (P = 0.02), CD34+/CD61- (P = 0.04) and total CD34+ cell dose (P = 0.04). Four parameters showed significant predictive power of early platelet engraftment, namely CD34+/CD61+ (P = 0.02), CD34+ /CD38- and total CD34+ cell dose (P = 0.04) and CD34+ /CD71- (P = 0.05). Comparing patients who received > to those who received < the threshold dose(s), only CD34+ /CD38- lost its significance for neutrophil engraftment; and only CD34+ /CD61+ retained its significance for platelet engraftment (P = 0.03); furthermore, the former group required significantly fewer platelet transfusions (P = 0.018). We concluded that in allogeneic PBSCT, the best predictor of early neutrophil engraftment is the absolute CD34+ /DR- and for early platelet engraftment is the absolute CD34+ /CD61+ cell dose.

Real-time process/quality control for HPC processing

BACKGROUND

JACIE Standards (FACT Standards in the USA) have been implemented in Europe since 1999. An on-site accreditation inspection took place at our center in January 2004. The purpose of this work was to develop a real-time process/quality control system meeting the JACIE Standards for HPC release.

METHODS

Data from 194 HPC processing procedures for autologous transplantation performed over a 5-year period were analyzed. The results of different processing methods applied at our facility were compared: (1) cryopreservation without washing cells (n=50), (2) washing cells (n=87), (3) cell-density separation (n=12) and (4) positive CD34 selection (n=45).

RESULTS

Four critical control points were set for the validation of HPC processing: (a) number of lost CD34(+) cells during processing, (b) contamination, (c) viability of the cells after thawing and (d) ability to reconstitute hematopoiesis after transplantation. On the basis of statistical analysis, ranges of acceptable values were defined for each critical control point and for each processing method. Those acceptable values were used for cell release and real-time quality control.

DISCUSSION

This study describes a model for the validation of HPC processing and for a real-time process/quality control system for HPC release. Optimization of processing techniques, standardization of methods and comparison between facilities will open the way towards external quality controls and quality improvement.

CD34+ and endothelial progenitor cells in patients with various degrees of congestive heart failure

BACKGROUND

Peripheral blood CD34(+) cells and circulating endothelial progenitor cells (EPCs) increase in myocardial infarction and vascular injuries as a reflection of endothelial damage. Despite the occurrence of endothelial dysfunction in heart failure (HF), no data are available on EPC mobilization in this setting. We investigated the pattern of CD34(+) cells and EPC mobilization during HF and their correlation with the severity and origin of the disease.

METHODS AND RESULTS

Peripheral blood CD34(+) cells (n=91) and EPCs (n=41), assessed both as CD34(+) cells coexpressing AC133 and vascular endothelial growth factor (VEGF) receptor-2 and as endothelial colony-forming units, were studied in HF patients (mean age 67+/-11 years) and 45 gender- and age-matched controls. Tumor necrosis factor-alpha (TNF-alpha) and its receptors (sTNFR-1 and sTNFR-2), VEGF, stromal derived factor-1 (SDF-1), granulocyte-colony stimulating factor (G-CSF), and B-type natriuretic peptide were also measured. CD34(+) cells, EPCs, TNF-alpha and receptors, VEGF, SDF-1, and B-type natriuretic peptide were increased in HF. CD34(+) cells and EPCs were inversely related to functional class and to TNF-alpha, being decreased in New York Heart Association class IV compared with class I and II and controls. No role was found for the origin of the disease.

CONCLUSIONS

CD34(+) cells and EPC mobilization occurs in HF and shows a biphasic response, with elevation and depression in the early and advanced phases, respectively. This could be related to the myelosuppressive role of TNF-alpha.

Kinetics of peripheral blood stem cell mobilization following G-CSF-supported chemotherapy

It would be a clinical and economical advantage if the optimal time point of peripheral blood stem cell (PBSC) mobilization following G-CSF-supported chemotherapy (CT) was known in advance. Therefore, we retrospectively analyzed mobilization parameters in 113 adult tumor patients treated in our institution within 1 year. The start of apheresis was guided by CD34(+) cell measurements in the PB and occurred on or after day 11 after start of mobilization CT in 97% of patients. The median peak (p)CD34(+) cell count in PB uniformly occurred on day 14-15 (range: 6-32 days) after the start of CT, irrespective of the diagnosis (multiple myeloma n = 76, other histology n = 37), the type, but not the amount, of premobilization CT or radiotherapy (RT), the mobilization regimen, or the G-CSF dosage administered. Among more heavily pretreated patients (>six cycles of prior CT or RT), a higher proportion mobilized late (pCD34(+) cell count later than day 20 in 12% and 13%, respectively, versus 2%-5% in the other groups). Therefore, we propose to start measuring CD34(+) cells in the PB on day 11 after the start of mobilization therapy. The wide range of optimal mobilization time points argues for an individualized rather than a preset start of apheresis.

Comparison of flow cytometry and laser scanning cytometry for the analysis of CD34+hematopoietic stem cells

BACKGROUND

Characterization of hematopoietic stem cells (HSCs) by laser scanning cytometry (LSC) was compared with conventional flow cytometry (FCM). The method was evaluated for application in the development of advanced cell culture substrates that were supposed to support the ex vivo expansion of HSC. For this purpose, adherent HSCs were grown in culture on thin polymer films coated with reconstituted collagen I fibrils and subsequently analyzed by LSC.

METHODS

CD34+ HSCs were isolated from cord blood by immunomagnetic separation and cultivated on polymer films coated with reconstituted collagen I fibrils. Cell surface antigens (CD34, CD29) were stained with antibodies, and nuclei were labeled with a DNA stain (TO-PRO-3 iodide) that does not interfere with the fluorochromes of the antibodies. Fluorescence intensity of the adherent cells was measured by means of LSC. Before and after in vitro expansion for time periods of up to 7 days, suspension cells were analyzed with LSC and FCM.

RESULTS

LSC-based analysis enabled reliable quantification of CD34+ cells with bright antigen expression before cell culture. At this stage, LSC and FCM data for CD34 expression at given HSC samples largely coincided. After in vitro expansion, LSC data deviated from FCM data for cells with dim CD34 antigen expression, whereas the fluorescence intensity of the CD29 antigen remained comparable. The deviation between LSC and FCM data for CD34dim was attributed to the better resolution of weak fluorescence by FCM. Based on the preceding evaluation of the method, LSC analysis could be applied to characterize HSCs cultivated on collagen I-coated polymer films without detachment of the cells from the substrate.

CONCLUSIONS

LSC-based analysis allows for the automated evaluation of adherent HSCs. Although resolution of weakly expressed antigens can be achieved more precisely with FCM, the method provides a valuable tool to study interactions of HSCs with bioartificial substrates.