Comparison of single and dual-platform assay formats for CD34+ haematopoietic progenitor cell enumeration

Validation of the single-platform ISHAGE protocol for enumeration of CD34+ hematopoietic stem cells in umbilical cord blood in a Brazilian center

Background

This study aims to validate the single-platform method for enumeration of CD34+ cells, by comparing the performance of two different commercial kits, as well as to evaluate the efficiency of the Accuri^TM C6 cytometer in providing direct counts of absolute cell numbers.

Method

We evaluated 20 samples from umbilical cord blood (UCB), comparing the two different methodologies for enumeration of CD34+ cells: single and dual-platform. For the assessment of the single-platform, Procount and SCE kits were used, both of which use fluorescent beads as a counting reference to obtain absolute CD34+ cells numbers. Moreover, after the acquisition of samples in flow cytometer Accuri^TM C6, following the protocol established for each kit, the number of CD34+ cells was recalculated, considering the cell count provided by the Accuri^TM C6.

Main Results

In our analysis, the results showed a strong correlation between the number of CD34+ cells/μL (r² = 0.77) when comparing the SCE kit and the current dual-platform method. On the other hand, the comparison between Procount kit and dual-platform results showed a moderate correlation for the number of CD34+/μL cells (r² = 0.64).

Conclusion

Our results showed that the Accuri^TM C6 flow cytometer can be used safely, applying both the dual and single platform analysis strategy. Considering the ISHAGE protocol-based single-platform approach, as the most appropriate methodology for CD34+ cells enumeration, our results demonstrated that the SCE kit has great potential for national standardization of UCB samples analysis methodology.

Role and analysis of monocyte subsets in cardiovascular disease. Joint consensus document of the European Society of Cardiology (ESC) Working Groups "Atherosclerosis & Vascular Biology" and "Thrombosis"

Monocytes as cells of the innate immunity are prominently involved in the development of atherosclerotic lesions. The heterogeneity of blood monocytes has widely been acknowledged by accumulating experimental and clinical data suggesting a differential, subset-specific contribution of the corresponding subpopulations to the pathology of cardiovascular and other diseases. This document re-evaluates current nomenclature and summarises key findings on monocyte subset biology to propose a consensus statement about phenotype, separation and quantification of the individual subsets.

Fifteen years of external quality assessment in leukemia/lymphoma immunophenotyping in The Netherlands and Belgium: A way forward

In 1985, external quality assurance was initiated in the Netherlands to reduce the between-laboratory variability of leukemia/lymphoma immunophenotyping and to improve diagnostic conclusions. This program consisted of regular distributions of test samples followed by biannual plenary participant meetings in which results were presented and discussed. A scoring system was developed in which the quality of results was rated by systematically reviewing the pre-analytical, analytical, and post-analytical assay stages using three scores, i.e., correct (A), minor fault (B), and major fault (C). Here, we report on 90 consecutive samples distributed to 40-61 participating laboratories between 1998 and 2012. Most samples contained >20% aberrant cells, mainly selected from mature lymphoid malignancies (B or T cell) and acute leukemias (myeloid or lymphoblastic). In 2002, minimally required monoclonal antibody (mAb) panels were introduced, whilst methodological guidelines for all three assay stages were implemented. Retrospectively, we divided the study into subsequent periods of 4 ("initial"), 4 ("learning"), and 7 years ("consolidation") to detect "learning effects." Uni- and multivariate models showed that analytical performance declined since 2002, but that post-analytical performance improved during the entire period. These results emphasized the need to improve technical aspects of the assay, and reflected improved interpretational skills of the participants. A strong effect of participant affiliation in all three assay stages was observed: laboratories in academic and large peripheral hospitals performed significantly better than those in small hospitals. © 2015 International Clinical Cytometry Society.

Development of model for analysing respective collections of intended hematopoietic stem cells and harvests of unintended mature cells in apheresis for autologous hematopoietic stem cell collection

Hematopoietic stem cells (HSCs) required to perform peripheral hematopoietic autologous stem cell transplantation (APBSCT) can be collected by processing several blood volumes (BVs) in leukapheresis sessions. However, this may cause granulocyte harvest in graft and decrease in patient's platelet blood level. Both consequences may induce disturbances in patient. One apheresis team's current purpose is to improve HSC collection by increasing HSC collection and prevent increase in granulocyte and platelet harvests. Before improving HSC collection it seemed important to know more about the way to harvest these types of cells. The purpose of our study was to develop a simple model for analysing respective collections of intended CD34+ cells among HSC (designated here as HSC) and harvests of unintended platelets or granulocytes among mature cells (designated here as mature cells) considering the number of BVs processed and factors likely to influence cell collection or harvest. For this, we processed 1, 2 and 3 BVs in 59 leukapheresis sessions and analysed corresponding collections and harvests with a referent device (COBE Spectra). First we analysed the amounts of HSC collected and mature cells harvested and second the evolution of the respective shares of HSC and mature cells collected or harvested throughout the BV processes. HSC collections and mature cell harvests increased globally (p<0.0001) and their respective shares remained stable throughout the BV processes (p non-significant). We analysed the role of intrinsic (patient's features) and extrinsic (features before starting leukapheresis sessions) factors in collections and harvests, which showed that only pre-leukapheresis blood levels (CD34+cells and platelets) influenced both cell collections and harvests (CD34+cells and platelets) (p<0.001) and shares of HSC collections and mature unintended cells harvests (p<0.001) throughout the BV processes. Altogether, our results suggested that the main factors likely to influence intended HSC collections or unintended mature cell harvests were pre-leukapheresis blood cell levels. Our model was meant to assist apheresis teams in analysing shares of HSC collected and mature cells harvested with new devices or with new types of HSC mobilization.

Age-matched dendritic cell subpopulations reference values in childhood

Dendritic cells (DCs) are the most potent antigen-presenting cells and are the key link between the innate and adaptive immune response. Only a few reports with study populations of up to 50 individuals have been published with age-based reference values for DC subpopulations in healthy children. Therefore, we aimed to establish reference ranges in a larger study population of 100 healthy children, which allowed age-matched subgroups. Most previous studies were performed using a dual-platform approach. In this study, a single-platform approach in a lyse no-wash procedure was used. DC subpopulations were defined as follows: CD45(+) CD85k(+) HLA-DR(+) CD14(-) CD16(-) CD33(+) cells as myeloid DCs (mDCs) and CD45(+) CD85k(+) HLA-DR(+) CD14(-) CD16(-) CD123(+) cells as plasmacytoid DCs (pDCs). Reference ranges were established using a semi-parametric regression of age-matched absolute and relative DC counts. We found a significant decline with increasing age in the medians of mDCs (P = 0.0003) and pDCs per μl peripheral blood (PB) (P = 0.004) and in the 50%, 90% and 95% reference ranges. We also identified significantly lower absolute cell counts of mDCs per μl PB in girls than in boys for all age groups (P = 0.0015). Due to the larger paediatric study population and single-platform approach, this study may give a more precise overview of the normal age-matched development of DC subpopulations and may provide a basis for analyzing abnormal DC counts in different illnesses or therapies such as post stem cell transplantation.

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.

True volumetric method for flow cytometric enumeration of CD34 + stem cells and its agreement with a standard bead-based single-platform protocol

BACKGROUND AIMS

Stem cells are commonly enumerated with bead-based methods in blood and marrow progenitor cell transplantation centers. We compared the International Society of Hematotherapy and Graft Engineering (ISHAGE) bead-based method with a true volumetric one that obviates the use of fluorescent beads for enumeration.

METHODS

From 31 samples, including 15 peripheral blood samples and 16 leukapheresis products, CD34 (+) cells were enumerated with the single-platform bead-based ISHAGE method and a true volumetric method. After exclusion of two outliers, one from the peripheral blood group and the other from the leukapheresis group, the results were compared.

RESULTS

In the peripheral blood category, no significant difference was observed. However, a proportional systematic error was seen in the leukapheresis group. The systematic error was corrected in the leukapheresis group using a regression line equation. The 95% confidence interval of differences was [-5.83, 2.18] for the peripheral blood and [-38.40, 38.77] for the leukapheresis group after correction of the systematic error.

CONCLUSIONS

The true volumetric method is a simple and reliable approach that can be used instead of the more popular bead-based procedures.

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.

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.

Gene expression profiling in circulating endothelial cells from systemic sclerosis patients shows an altered control of apoptosis and angiogenesis that is modified by iloprost infusion

Introduction

Circulating endothelial cells are increased in patients affected by systemic sclerosis (SSc) and their number strongly correlates with vascular damage. The effects of iloprost in systemic sclerosis are only partially known. We aimed at studying the gene expression profile of circulating endothelial cells and the effects of iloprost infusion and gene expression in patients with systemic sclerosis.

Methods

We enrolled 50 patients affected by systemic sclerosis, 37 patients without and 13 patients with digital ulcers. Blood samples were collected from all patients before and 72 hours after either a single day or five days eight hours iloprost infusion. Blood samples were also collected from 50 sex- and age-matched healthy controls. Circulating endothelial cells and endothelial progenitors cells were detected in the peripheral blood of patients with systemic sclerosis by flow cytometry with a four-colour panel of antibodies. Statistical analysis was performed with the SPSS 16 statistical package.Circulating endothelial cells were then isolated from peripheral blood by immunomagnetic CD45 negative selection for the gene array study.

Results

The number of both circulating endothelial cells and progenitors was significantly higher in patients affected by systemic sclerosis than in controls and among patients in those with digital ulcers than in patients without them. Circulating endothelial cells and progenitors number increased after iloprost infusion. Gene array analysis of endothelial cells showed a different transcriptional profile in patients compared to controls. Indeed, patients displayed an altered expression of genes involved in the control of apoptosis and angiogenesis. Iloprost infusion had a profound impact on endothelial cells gene expression since the treatment was able to modulate a very high number of transcripts.

Conclusions

We report here that circulating endothelial cells in patients with systemic sclerosis show an altered expression of genes involved in the control of apoptosis and angiogenesis. Moreover we describe that iloprost infusion has a strong effect on endothelial cells and progenitors since it is able to modulate both their number and their gene expression profile.

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.

Increase in circulating bone marrow progenitor cells after myocardial infarction

BACKGROUND

Most circulating blood cells expressing the marker CD34 are bone marrow progenitor cells. These cells differentiate into cardiomyocytes, endothelial and smooth muscle cells after myocardial infarction in vivo. Mobilization of bone marrow progenitor cells into the peripheral blood after myocardial infarction may supply these cells to the heart. Rise in CD34+ cell concentrations following myocardial infarction would support the existence of myocardial-initiated mobilization.

METHODS

Serial measurements of circulating CD34+ cells were made in 42 consecutive patients presenting with first ST-elevation myocardial infarction. Measurement of serum concentrations of monocyte chemoattractant protein-1, stromal derived factor-1, hepatocyte growth factor, interleukin-17 and thrombopoietin was also performed. Samples were drawn on day 1 after myocardial infarction, and on days 4, 8 and 12. Levels of CD34+ cells and cytokines were also measured in 15 controls.

RESULTS

By day 8, the mean concentration of CD34+ cells rose by 74% above mean control level of 2527 cells/ml, and 41% above day 1 mean (P=0.02). This rise was sustained on day 12 (P=0.05). On day 1, there was a 9.3-fold rise in hepatocyte growth factor above the control level of 589 pg/ml (P=0.002). Hepatocyte growth factor levels declined from the day 1 mean of 6061 to 1485 pg/ml on day 12 (P=0.002). No significant change in stromal derived factor-1, interleukin-17, monocyte chemoattractant protein-1 and thrombopoietin was observed. Elevations in CD34+ cells and hepatocyte growth factor were not related to infarction size as estimated on echocardiography.

CONCLUSIONS

Elevation in the concentration of circulating CD34+ cells after myocardial infarction suggests that myocardial initiated bone marrow progenitor cell mobilization exists in humans. The cytokines studied in our protocol are not likely to play a direct role in bone marrow progenitor cell mobilization.

Administration of CD34+ cells after stroke enhances neurogenesis via angiogenesis in a mouse model

Thrombo-occlusive cerebrovascular disease resulting in stroke and permanent neuronal loss is an important cause of morbidity and mortality. Because of the unique properties of cerebral vasculature and the limited reparative capability of neuronal tissue, it has been difficult to devise effective neuroprotective therapies in cerebral ischemia. Our results demonstrate that systemic administration of human cord blood-derived CD34(+) cells to immunocompromised mice subjected to stroke 48 hours earlier induces neovascularization in the ischemic zone and provides a favorable environment for neuronal regeneration. Endogenous neurogenesis, suppressed by an antiangiogenic agent, is accelerated as a result of enhanced migration of neuronal progenitor cells to the damaged area, followed by their maturation and functional recovery. Our data suggest an essential role for CD34(+) cells in promoting directly or indirectly an environment conducive to neovascularization of ischemic brain so that neuronal regeneration can proceed.

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.

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.

Influence of preapheresis clinical factors on the efficiency of CD34+ cell collection by large-volume apheresis

We evaluated 120 leukapheresis procedures (93 patients), in order to detect clinical factors that influence the efficiency of CD34+ collection using Cobe Spectra trade mark cell separators. Hematocrit was >27% and platelet count >30 000/microl in >95% of patients. Platelet transfusions were given if the postprocedure count was &<20 000/microl. Multiple regression analysis was used to analyze putative factors, and a predictive equation defined by stepwise regression modeling. The mean efficiency was 0.59 (s.d. 0.27). Sex (M>F; P=0.01), the volume processed (inversely; P=0.01) and CD34+ cell count (inversely; P=0.04) were associated with efficiency, whereas hematocrit, platelet or leukocyte count, catheter type and patient weight were not. The effect size for predictive factors was small (R(2)=0.21). Adverse events were limited to hypocalcemia. We conclude that female sex, volume processed and CD34+ cell count adversely influence the efficiency of CD34+ cell leukapheresis. However, the impact of volume and CD34+ cell count is small, and likely to be offset by the influence of these same factors on overall yield. Leukapheresis appears to be safe and efficient for autologous blood and marrow transplantation patients with hematocrit >27% and platelet count >30 000/microl.

Increase of high fluorescence reticulocytes indicates mobilization of peripheral stem cells in children recovering from aplasia after chemotherapy or bone marrow transplantation

Enumeration of CD34 + cells is the standard assay procedure for optimization of peripheral blood stem cell harvesting. High fluorescence reticulocytes (HFR) have been shown to signal a rebound in haematopoiesis after chemotherapy. The aim of this study was to evaluate HFR determination, as compared to CD34 + cell counts and CFU-GM, as a potential predictor of PBSC counts after recovery from chemotherapy and/or bone marrow transplantation. Twenty-five paediatric patients undergoing intensive courses of chemotherapy and 9 undergoing bone marrow auto or allografts were investigated. In most of our cases, HFR recovered at the same time or earlier than CD34 + cells. Similarly, the rise in HFR preceeded the CFU-GM peak in most of these cases. In no case did we observe a CFU-GM peak without a rise in HFR%. In our experience, the daily relative HFR increase may be used to predict the optimal time for mobilization of stem cells and was therefore of value clinically to confirm the timing of apheresis.

A single-step colony-forming unit assay for unseparated mobilized peripheral blood, cord blood, and bone marrow

The colony-forming unit (CFU) assay is exposed to a lot of variation, part of which is introduced by several enrichment strategies that are routinely performed before assessment of clonogenic capacity in mobilized peripheral blood (PB), bone marrow (BM), or cord blood (CB). We investigated the possibility to perform a single-step CFU assay by direct plating of PB, BM, or CB into CFU culture medium to obtain more reproducible results than after a standard Ficoll or lysis procedure. Direct plating implies the presence of red blood cells (RBC), white blood cells (WBC), and plasma in the CFU assay, which could possibly influence the outcome of the assay. Of all components, only the RBC was found to negatively influence CFU-GM growth if a concentration of > 0.02 x 10(9)/ml was present in the CFU culture medium. Subsequently, depending on the RBC concentration PB, BM, and CB samples were prediluted in triplicate or quadruplicate and plated into CFU medium. Lysis and/or Ficoll procedures were also performed in triplicate or quadruplicate on the same samples, and the mean colony number and coefficient of variation (CV) of the three techniques were compared. Significantly smaller CV values were found using the direct plating technique (all assays, mean 7.5%, range 1.6-15.6%) than after Ficoll separation (mean 18.0%, range 2.2-62.5%). Intermediate results were obtained with the lysis method (mean CV 11.6%, range 3.3-29%). In most samples, and especially in those with a very low number of clonogenic cells per milliliter, more colonies were detected with the direct plating method than with either the lysis or Ficoll method. In conclusion, the single-step direct plating method significantly enhances reproducibility of the CFU assay for PB, BM, and CB samples in comparison with standard techniques by circumvention of loss of colony formation and by decreasing variability. Furthermore, the direct plating technique is a timesaving assay.

Flow cytometric enumeration and immunophenotyping of hematopoietic stem and progenitor cells

Flow cytometric enumeration of CD34(+) hematopoietic stem and progenitor cells (HPC) is widely used to evaluate the adequacy of peripheral blood stem cell grafts and is also useful for planning the apheresis sessions needed to obtain these grafts. A state-of-the-art method to enumerate CD34(+) cells has been developed that makes use of a multiparameter definition of HPC, based on their light scatter characteristics and dim expression of CD45, utilizing fluorescent counting beads. This approach allows the absolute CD34(+) cell count to be determined directly from a flow cytometer. The method can be extended with a viability stain and additional markers for further immunologic characterization of CD34(+) cells, and has been successfully implemented in multicenter trials. Using such a standardized assay, it should be possible to define more accurately the lower threshold for a safe HPC graft in terms of short- and long-term hematopoietic reconstitution. Semin Hematol 38:139-147.

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

The enumeration of absolute levels of cells and their subsets in clinical samples is of primary importance in human immunodeficiency virus (HIV)+ individuals (CD4+ T- lymphocyte enumeration), in patients who are candidates for autotransplantation (CD34+ hematopoietic progenitor cells), and in evaluating leukoreduced blood products (residual white blood cells). These measurements share a number of technical options, namely, single- or multiple-color cell staining and logical gating strategies. These can be accomplished using single- or dual-platform counting technologies employing cytometric methods. Dual-platform counting technologies couple the percentage of positive cell subsets obtained by cytometry and the absolute cell count obtained by automated hematology analyzers to derive the absolute value of such subsets. Despite having many conceptual and technical limitations, this approach is traditionally considered as the reference method for absolute cell count enumeration. As a result, the development of single-platform technologies has recently attracted attention with several different technical approaches now being readily available. These single-platform approaches have less sources of variability. A number of reports clearly demonstrate that they provide better coefficients of variation (CVs) in multicenter studies and a lower chance to generate aberrant results. These methods are therefore candidates for the new gold standard for absolute cell assessments. The currently available technical options are discussed in this review together with the results of some cross-comparative studies. Each analytical system has its own specific requirements as far as the dispensing precision steps are concerned. The importance of precision reverse pipetting is emphasized. Issues still under development include the establishment of the critical error ranges, which are different in each test setting, and the applicability of simplified low-cost techniques to be used in countries with limited resources.