Affordable CD4+ T cell counts by flow cytometry. II. The use of fixed whole blood in resource-poor settings

Application of advanced technology in traditional Chinese medicine for cancer therapy

Although cancer has seriously threatened people’s health, it is also identified by the World Health Organization as a controllable, treatable and even curable chronic disease. Traditional Chinese medicine (TCM) has been extensively used to treat cancer due to its multiple targets, minimum side effects and potent therapeutic effects, and thus plays an important role in all stages of tumor therapy. With the continuous progress in cancer treatment, the overall efficacy of cancer therapy has been significantly improved, and the survival time of patients has been dramatically prolonged. In recent years, a series of advanced technologies, including nanotechnology, gene editing technology, real-time cell-based assay (RTCA) technology, and flow cytometry analysis technology, have been developed and applied to study TCM for cancer therapy, which efficiently improve the medicinal value of TCM and accelerate the research progress of TCM in cancer therapy. Therefore, the applications of these advanced technologies in TCM for cancer therapy are summarized in this review. We hope this review will provide a good guidance for TCM in cancer therapy.

An easy and reliable whole blood freezing method for flow cytometry immuno-phenotyping and functional analyses

BACKGROUND

Immune profiling by flow cytometry is not always possible on fresh blood samples due to time and/or transport constraints. Furthermore, the cryopreservation of peripheral blood mononuclear cells (PBMC) requires on-site specialized lab facilities, thus severely restricting the extent to which blood immune monitoring can be applied to multicenter clinical studies. These major limitations can be addressed through the development of simplified whole blood freezing methods.

METHODS

In this report, we describe an optimized easy protocol for rapid whole blood freezing with the CryoStor® CS10 solution. Using flow cytometry, we compared cellular viability and composition on cryopreserved whole blood samples to matched fresh blood, as well as fresh and frozen PBMC.

RESULTS

Though partial loss of neutrophils was observed, leucocyte viability was routinely >75% and we verified the preservation of viable T cells, NK cells, monocytes, dendritic cells, and eosinophils in frequencies similar to those observed in fresh samples. A moderate decrease in B cell frequencies was observed. Importantly, we validated the possibility to analyze major intracellular markers, such as FOXP3 and Helios in regulatory T cells. Finally, we demonstrated good functional preservation of CS10-cryopreserved cells through the analysis of intracellular cytokine production in ex vivo stimulated T cells (IFNg, IL-4, IL-17A,) and monocytes (IL-1b, IL-6, TNFa).

CONCLUSIONS

In conclusion, our protocol provides a robust method to apply reliable immune monitoring studies to cryopreserved whole blood samples, hence offering new important opportunities for the design of future multicenter clinical trials.

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.

Interlaboratory comparison of the TransFix®/EDTA Vacuum Blood Collection tube with the 5 mL Cyto-Chex® BCT

BACKGROUND

An interlaboratory study was performed to compare the performance of the 3 mL TransFix®/EDTA Vacuum Blood Collection Tube (TVT), with the 5 mL Cyto-Chex® BCT tube (BCT). Both devices are intended for collection and storage of whole blood specimens for immunophenotyping of leukocytes by flow cytometry for up to 14 days.

METHODS

One site in the United States and two in the United Kingdom tested samples from 10 HIV positive patients and four healthy subjects for a total of 42 samples. From each subject, three blood samples were collected: a BD 4 mL K₃ EDTA Vacutainer (Vacutainer), a TVT, and a BCT. At all sites, samples were analyzed on a BD FACS Canto II flow cytometer for a full lymphocyte subset count within 6 h of collection (all devices) and on Day 11 and Day 15 (TVT and BCT only). Data obtained from the Vacutainer were used as the control data set with which TVT and BCT data were statistically compared.

RESULTS AND CONCLUSIONS

Statistical concordance was demonstrated for both devices in relation to cell absolute count recovery. For cell marker signal, both devices exhibited a significant decrease in mean fluorescence intensity (MFI) for the detection of lymphocyte subsets and their target markers. There was a marked increase in autofluorescence observed for BCT stabilized lymphocytes whereas values for the TVTs were comparable to the control. There were eight instances of statistical equivalence between the level of antibody autofluorescence observed in the control tube and the TVT across both patient cohorts, versus two for the BCT. © 2018 International Clinical Cytometry Society.

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.

Gene expression profiling of immunomagnetically separated cells directly from stabilized whole blood for multicenter clinical trials

Background

Clinically useful biomarkers for patient stratification and monitoring of disease progression and drug response are in big demand in drug development and for addressing potential safety concerns. Many diseases influence the frequency and phenotype of cells found in the peripheral blood and the transcriptome of blood cells. Changes in cell type composition influence whole blood gene expression analysis results and thus the discovery of true transcript level changes remains a challenge. We propose a robust and reproducible procedure, which includes whole transcriptome gene expression profiling of major subsets of immune cell cells directly sorted from whole blood.

Methods

Target cells were enriched using magnetic microbeads and an autoMACS® Pro Separator (Miltenyi Biotec). Flow cytometric analysis for purity was performed before and after magnetic cell sorting. Total RNA was hybridized on HGU133 Plus 2.0 expression microarrays (Affymetrix, USA). CEL files signal intensity values were condensed using RMA and a custom CDF file (EntrezGene-based).

Results

Positive selection by use of MACS® Technology coupled to transcriptomics was assessed for eight different peripheral blood cell types, CD14+ monocytes, CD3+, CD4+, or CD8+ T cells, CD15+ granulocytes, CD19+ B cells, CD56+ NK cells, and CD45+ pan leukocytes. RNA quality from enriched cells was above a RIN of eight. GeneChip analysis confirmed cell type specific transcriptome profiles. Storing whole blood collected in an EDTA Vacutainer® tube at 4°C followed by MACS does not activate sorted cells. Gene expression analysis supports cell enrichment measurements by MACS.

Conclusions

The proposed workflow generates reproducible cell-type specific transcriptome data which can be translated to clinical settings and used to identify clinically relevant gene expression biomarkers from whole blood samples. This procedure enables the integration of transcriptomics of relevant immune cell subsets sorted directly from whole blood in clinical trial protocols.

Opportunities to improve storage and transportation of blood specimens for CD4 testing in a rural district in Zimbabwe using BD vacutainer CD4 stabilization tubes: a stability and diagnostic accuracy study

Background

CD4+ T-cell testing of blood specimens collected in standard EDTA Vacutainer tubes and transported at ambient temperature, must be completed within 48 hours with the BD FACSCount™ flow cytometer, restricting specimen collection in remote clinics with no on-site testing and limited specimen transport services. We conducted a study in Buhera District, Zimbabwe, to assess the stability and accuracy of CD4+ T-cell results of samples collected in Stabilization Tubes (ST) and stored at ambient temperature for varying time periods.

Methods

Paired EDTA and ST samples were collected from 51 HIV-positive patients aged 18 years and older. CD4+ T-cell testing was done on arrival in the laboratory (Day 0). ST samples were retested on Days 3, 5, and 7. Nineteen ST samples were stored for an additional week and retested on Day 14.

Results

There was a strong correlation between absolute CD4+ T-cell counts measured in the EDTA Day 0 reference sample and Day 7 ST sample (Spearman's rho: 0.9778; mean difference: -4.9 cells/μL and limits of agreement (LOA): 98.5 and 88.7 cells/μL); and the reference sample and Day 14 ST sample (Spearman's rho: 0.9632; mean difference 5.1 cells/μL and LOA: -99.6 and 109.8 cells/μL. Using a 350 cells/μL threshold, the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were all 100% on Day 7, and 83.3%, 100%, 100% and 92.9% on Day 14. Using a 500 cells/μL threshold, the sensitivity, specificity, PPV and NVP were 100%, 88.5%, 88.5% and 100% on Day 7 and 88.9%, 80.0%, 80.0% and 88.9% on Day 14.

Conclusions

CD4 ST can be used and stored up to 7 days as a reliable alternative to standard EDTA tubes in settings where CD4+ T-cell testing within 48 hours is not feasible. Despite the small sample size, results suggest that ST may be stored up to 14 days at room temperature for CD4 testing, without compromising accuracy. However, further studies with larger sample sizes are needed to confirm this preliminary finding.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0553-9) contains supplementary material, which is available to authorized users.

Field evaluation in Chad of community usage of CD4 T lymphocyte counting by alternative single-platform flow cytometry

Background

Field and community evaluation of the routine usage of CD4 T counting platforms is essential in resource-poor countries for efficient and cost-effective monitoring of HIV-infected adults and children attending health care centers.

Methods

We herein addressed the principal issues raised by the implementation of the single-platform, volumetric Auto40 flow cytometer (Apogee Flow Systems Ltd, Hemel Hempstead, UK) in 8 community HIV monitoring laboratories of different levels throughout Chad. This is a country with particularly difficult conditions, both in terms of climate and vast geographical territory, making the decentralization of the therapeutic management of HIV-infected patients challenging.

Results

The routine usage of the Auto40 flow cytometers for a period of 5 years (2008–2013) confirms the reliability and robustness of the analyzer for community-based CD4 T cell enumeration in terms of both absolute numbers and percentages to enable accurate monitoring of HIV-infected adults and children. However, our observations suggest that the Auto40 mini flow cytometer is not suitable for all laboratories as it is oversized and ultimately very expensive.

Conclusion

The Chad experience with the Auto40 flow cytometer suggests that its usage in resource-limited settings should be mainly reserved to reference (level 1) or district (level 2) laboratories, rather than to laboratories of health care centres (level 3).

Validation of a single-platform, volumetric, CD45-assisted PanLeucogating Auto40 flow cytometer to determine the absolute number and percentages of CD4 T cells in resource-constrained settings using Cameroonian patients' samples

The study evaluated the single-platform, volumetric, CD45-assisted PanLeucogating Auto40 flow cytometer (Apogee Flow Systems Ltd., Hemel Hempstead, United Kingdom) for CD4 T cell numeration, compared to the reference FACSCalibur flow cytometer. Results of absolute counts and percentages of CD4 T cells by Auto40 and FACSCalibur of 234 tripotassium EDTA (K3-EDTA)-blood samples from 146 adults and 88 children (aged from 18 months to 5 years), living in Yaoundé, Cameroon, were highly correlated (r(2) = 0.97 and r(2) = 0.98, respectively). The mean absolute bias and relative bias between Apogee Auto40 and FACSCalibur absolute CD4 T cell counts were +9.6 cells/μl, with limits of agreement from -251 to 270 cells/μl, and +4.1%, with limits of agreement from -16.1 to 24.4%, respectively. The mean absolute bias and relative bias between Apogee Auto40 and FACSCalibur CD4 T cell results expressed as percentages were +0.05% CD4 (95% confidence interval [CI], -0.03 to 0.41), with limits of agreement from -6.0 to 5.9% CD4, and +1.0%, with limits of agreement from -32.3 to 34.4%, respectively. The Auto40 counting allowed identification of the majority of adults with CD4 T cell counts below 200 cells/μl (sensitivity, 87%; specificity, 98%) or below 350 cells/μl (sensitivity, 92%; specificity, 98%) and of children with CD4 T cell counts below 750 cells/μl (sensitivity, 82%; specificity, 98%) or below 25% CD4(+) (sensitivity, 96%; specificity, 99%). The Auto40 analyzer is a reliable alternative flow cytometer for CD4 T lymphocyte enumeration to be used in routine immunological monitoring according to the WHO recommendations for HIV-infected adults as well as children living in resource-constrained settings.

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.

Flow cytometric profiles, biomolecular and morphological aspects of transfixed leukocytes and red cells

BACKGROUND

We evaluated the effects of the TransFix(TM) short-term stabilization technique on leukocyte subpopulations in both optimal and adverse storage temperatures and on different cellular concentrations. Particularly, we analyzed DNA cell content and membrane structure also for erythrocytes using a multiparametric approach.

METHODS

We studied biomolecular and morphological aspects of transfixed cells, by means of SEM, TEM, Western blotting, and by flow cytometry (FC). Furthermore, FC, Tunel, and electrophoresis were applied to evaluate DNA behavior.

RESULTS

We confirm preservation of scatter characteristics and immunophenotyping, extending such evaluations to cells stored in suboptimal conditions (25 degrees C and 37 degrees C) and in high density. Data demonstrate for lymphomonocytic cells an optimal conservation, slightly decreasing at higher temperatures for both 1/5 and 1/10 ratio (TransFix/sample), with enhanced autofluorescence. Eosinophils, basophils, and neutrophils are shown to preserve differently over time. The three different cellular concentrations evaluated (30,000-120,000 cell/microl) demonstrate substantial stability in FI values. Furthermore DNA content analysis attests the absence of any apoptotic pattern. Transfixed red cell protein profile as well as their morphological features appears almost unaltered.

CONCLUSIONS

Cytometric performance is suboptimal in aged unfixed specimens because of apoptosis that affects light scatter properties. Our findings highlight that lymphomonocytic cells are well stabilized even at suboptimal temperature and cell density. TransFix is able to abolish any apoptotic features and acts as an optimal blood preservative for appropriate preanalytical stabilization.

Challenges in implementing CD4 testing in resource-limited settings

The scale-up of HIV antiretroviral therapy in recent years has led to a rapid increase in CD4 and CD4% count capacity to meet the diagnostic needs of staging and monitoring disease progression and treatment efficacy in adults and infants. The speed of implementation of this technology has been unrivalled in recent years and has met challenges with technology selection, laboratory infrastructure development, human resource limitations, cost-effectiveness, instrument maintenance, and ensuring testing access and quality. The lessons learned from dealing with these challenges have helped strengthen existing laboratory systems for other diagnostics. They may also facilitate the implementation of new diagnostics in future.

Long-term stabilized blood samples as controls for flow cytometric HLA-B27 screening: a feasibility study

BACKGROUND

Long-term stabilized blood samples are potentially useful as positive or negative procedure controls for flow cytometric HLA-B27 screening, and could serve as test samples in an external quality assessment (EQA) scheme. We evaluated long-term stabilized whole blood specimens as prepared for the UK NEQAS for Leucocyte Immunophenotyping EQA scheme (Sheffield, UK).

METHODS

Peripheral blood samples were obtained from nine blood bank donors with known HLA-B typing. Short-term stabilization with Trans-FIXtrade mark was performed before shipment to Sheffield. Thereafter, long-term stabilization was performed. Commercially available HLA-B27 mAb were tested periodically between 1 week and 12 months on (i) fresh, (ii) short-term stabilized, and (iii) long-term stabilized blood samples using a stain, lyse, and wash technique. We compared the forward scatter (FSC), sideward scatter (SSC), and fluorescence signals of lymphocytes as a function of time. Furthermore, a pilot send-out with stabilized blood samples of four blood bank donors was distributed among the participants to the Benelux EQA scheme for HLA-B27 screening, and results were compared with historical EQA data obtained using nonstabilized blood samples from the same donors.

RESULTS

There were no major effects on FSC and SSC characteristics of lymphocytes. Background fluorescence of stabilized samples increased and specific fluorescence of stabilized HLA-B27 positive samples decreased as compared with fresh samples. However, discrimination between the investigated HLA-B27 positive and HLA-B27 negative samples remained feasible poststabilization. In the pilot send-out, the results obtained with stabilized samples were less concordant than with the corresponding fresh samples due to variable quality of the stabilized samples.

CONCLUSION

Long-term stabilized whole blood samples are potentially useful as true HLA-B27 positive and true HLA-B27 negative control cells for daily and longitudinal quality control of flow cytometric HLA-B27 screening. In the same way, long-term stabilized samples may be used for EQA purposes. However, these samples are currently not feasible for reagent validation purposes. Extensive quality control of long-term stabilized samples is necessary before distribution in multicenter surveys.

Flow cytometric determination of residual white blood cell levels in preserved samples from leukoreduced blood products

BACKGROUND

In preparation for a proposed consolidated testing service, Canadian Blood Services undertook the evaluation of a commercial test kit for the enumeration by flow cytometry of residual white blood cells (rWBCs) present in preserved samples recovered from leukoreduced (LR) blood and platelet products.

STUDY DESIGN AND METHODS

The stability of preserved WBCs, the equivalency of WBCs used for spiking, test method precision, specificity, reliability, accuracy, and sensitivity were investigated. For comparative purposes, WBC counts were also determined by Nageotte as well as by flow cytometry.

RESULTS

WBCs were stable up to 4 weeks at room temperature for all components by either method. Within methods, no differences were observed due to the source of WBC used for spiking purposes. By either method, test precision was acceptable (<20% coefficient of variation) and of similar reliability at a target value of 10 +/- 5 WBCs per microL. The flow cytometric method was shown to be more specific and accurate than the Nageotte method. Sensitivity by either method was 0.1 WBCs per microL. On average, Nageotte counts were lower than those observed by flow cytometry.

CONCLUSIONS

These results demonstrate that WBCs in WBC stabilizing solution-treated samples from LR blood components were stabilized up to 4 weeks at room temperature and that rWBC determinations made with a WBC enumeration kit by flow cytometry have the required precision, specificity, reliability, and accuracy in the relevant test range. This validated WBC stabilization and flow cytometric counting method is considered acceptable as part of a quality control program for leukoreduced blood products.

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

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

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

OBJECTIVES

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

DESIGN

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

SETTING

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

PARTICIPANTS

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

MAIN OUTCOME MEASURES

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

RESULTS

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

CONCLUSIONS

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

Effect of ex vivo storage and Cyto-Chex on the expression of P-selectin glycoprotein ligand-1 (PSGL-1) on human peripheral leukocytes

P-selectin glycoprotein ligand-1 (PSGL-1) is expressed on leukocytes and its expression is elevated in asthma and chronic obstructive pulmonary disease. This study assessed whether the cell stabilisation solution Cyto-Chex is able to preserve such quantitative differences for delayed testing. Peripheral blood was mixed with Cyto-Chex and stored refrigerated or at ambient temperature. Aliquots were tested by flow cytometry 2 to 168 h after collection for PSGL-1, CD3, CD4, CD8, and CD16 expression and marker-positive cell counts. Compared with controls a marked reduction of staining intensities is seen at all time points for all markers, irrespective of the storage temperature. This loss of bright staining did not or only moderately decrease marker-positive cell counts except for PSGL-1+ lymphocytes which declined in parallel with staining intensity. These findings indicate that Cyto-Chex is not able to preserve the expression or affinity to antibodies of surface markers to allow delayed determination of quantitative differences or detection of weakly staining cells. Immunophenotyping is mostly possible for 7 days after collection, however, this has to be tested for each marker and cell type of interest.

Efficacy of Cyto-Chex Blood Preservative for Delayed Manual CD4 Testing Using Dynal T4 Quant CD4 Test Among HIV-Infected Persons in Zambia

BACKGROUND

Manual CD4 tests such as Dynal T4 Quant (Dynabeads, Dynal Biotech, Oslo, Norway) are less expensive alternatives to flow cytometry in resource-limited countries. Whereas blood preservatives have proven useful for stabilizing blood samples to allow delayed CD4 testing by flow cytometry, they have not been verified for manual tests. A method for preservation of blood prior to manual CD4 testing is needed for long-distance transport or sample batching.

METHODS

Blood from HIV-positive Zambian military beneficiaries was mixed (1:1) with Cyto-Chex (Streck Laboratories, La Vista, NE) blood preservative, and the blood was stored at refrigerated, ambient, and incubator (37 degrees C) temperatures prior to Dynabeads CD4 testing at 0, 3, 6, and 9 days after collection. Baseline flow cytometry and Dynabeads testing without preservative were performed for comparison.

RESULTS

Twenty-seven patient samples were analyzed. Dynabeads vs. flow cytometry had a correlation coefficient (r) of 0.84. There was excellent correlation (r = 0.96) between baseline Dynabeads testing and Cyto-Chex-preserved samples. Refrigerated samples showed strong correlation with baseline Dynabeads (r = 0.93-0.95) on days 3, 6, and 9 without decline in CD4 count (P = 0.73). Samples stored at ambient temperature yielded inferior results (r = 0.76-0.81), with a significant decline in CD4 count by day 3 (P < 0.001). The incubator arm had especially poor correlation (r = 0.30-0.49).

CONCLUSIONS

Addition of Cyto-Chex to peripheral blood (1:1) adequately preserves refrigerated blood samples for up to 9 days for subsequent testing with Dynabeads CD4 test. Cyto-Chex, however, cannot be recommended for delayed Dynabeads CD4 testing with storage at 37 degrees C or ambient temperatures in tropical areas similar to the site of this study.

Low cost CD4 enumeration using generic monoclonal antibody reagents and a two-color user-defined MultiSET™ protocol

BACKGROUND

The standard three-tube, three-color flow cytometric method utilizing the TriTEST reagents in conjunction with the MultiSET software commonly used in most laboratories in Thailand for CD4 enumeration is expensive and thus unavailable to most HIV-infected patients. A more affordable method, i.e., the PanLeucogating protocol using only two monoclonal antibody reagents, has been described but requires the use of the CellQUEST software that does not have automatic gating and reporting facilities. We describe a simple protocol that utilizes a two-color user-defined protocol with the automated MultiSET software for the acquisition, analysis, and reporting of CD4 results.

METHODS

A two-color user-defined protocol was set up following instructions in the Becton Dickinson Biosciences MultiSET manual, adhering strictly to the information regarding the Gate and Attractor Hierarchy for analyzing various reagent combinations. This simple two-color user-defined MultiSET software was evaluated using generic monoclonal reagents in comparison with the standard TriTEST/MultiSET protocol.

RESULTS

The two-color user-defined MultiSET software is easy to use. It requires only modification of the original MultiSET program and the results obtained are comparable with those derived from the standard TriTEST/MultiSET protocol.

CONCLUSION

The use of this easy and reliable two-color user-defined MultiSET protocol represents an affordable alternative to CD4 testing in resource-poor settings.

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

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

A multicenter evaluation of the PanLeucogating method and the use of generic monoclonal antibody reagents for CD4 enumeration in HIV-infected patients in Thailand

BACKGROUND

The current method of CD4 enumeration in Thailand, based on the three-tube, three-color method recommended by the Centers for Disease Control and Prevention, is expensive and thus unavailable to most patients who have the human immunodeficiency virus (HIV). Less expensive, simpler protocols (i.e., PanLeucogating and primary CD4 gating) have been described but require more published validation data to gain widespread acceptance. We describe a multicenter evaluation of the PanLeucogating method.

METHODS

The PanLeucogating method using generic reagents was evaluated in comparison with the standard three-tube, three-color method using commercial reagents. Percentage of CD4+ T cells among lymphocytes and absolute CD4+ T-cell counts were determined in 611 HIV-infected individuals recruited from four sites. Linear regression and Bland-Altman tests were used for statistical analysis.

RESULTS

The correlation of percentage of CD4+ T cells and absolute CD4+ T-cell counts obtained with the PanLeucogating strategy and the standard predicate method was high (r2 = 0.96 and 0.95, respectively, for the entire study population and r2 > 0.95 and 0.93, respectively, for each study group). Absolute CD4+ T-cell counts of the overall study pool and of the two subdivisions of absolute CD4+ T-cell counts (i.e., 0-250 cells/microl and > 250 cells/microl) derived from the two methods demonstrated excellent agreement, with mean biases of +18 cells/microl, +11 cells/microl, and +24 cells/microl, respectively.

CONCLUSIONS

These observations demonstrate that CD4 enumeration by PanLeucogating is reliable and can be performed to an identical standard in a quality-assured network of collaborating laboratories as a new cost-effective approach to HIV monitoring.

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.

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

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

Fixation and cryopreservation of whole blood and isolated mononuclear cells: Influence of different procedures on lymphocyte subset analysis by flow cytometry

BACKGROUND

Immunophenotyping of whole blood (WB) and isolated peripheral blood mononuclear cells (PBMCs) is a common tool used to evaluate immune system changes in clinical studies. The development of methods that would allow preservation of samples for flow cytometric analysis is important for the extension of this technology to field testing in settings where the equipment might be not readily accessible.

METHODS

Three-color flow cytometric analysis was used to determine percentages of T cells and their subsets (CD3(+), CD4(+), CD8(+)), B cells (CD19(+)), and natural killer cells (CD16(+)/56(+)) in WB and PBMCs using variations of a standard stain/fix WB staining procedure (Optilyse) that included staining following fixation and freezing of fixed samples before or after staining.

RESULTS

Comparable lymphocyte subset percentages in WB or PBMCs were observed regardless of Optliyse method used (all Ps >/= 0.8). However, differences in fluorescence intensity for several markers were observed across procedures. Compared with the standard stain/fix procedures, fix/stain decreased the mean fluorescence intensities for CD4, CD8, CD19 and CD16/56 in WB and PBMCs (P </= 0.03 for these markers P = 0.105 for CD8 in PBMCs). Further decreases in mean fluorescence intensity were seen with the fix/stain/freeze procedure. The stain/fix/freeze yielded intensities largely comparable to those seen with standard stain/fix procedure (P >/= 0.13), suggesting that, when the markers of interest are known at the time of field collection, implementation of this procedure might be desirable. Fix/freeze/stain resulted in diminution of intensity in general, but they tended to be more modest than those seen for fix/stain/freeze and therefore might be applicable to field studies in instances when the specific markers of interest cannot be defined upfront.

CONCLUSIONS

Freezing of fixed WB and PBMCs before or after cell surface staining is a reliable method for preserving specimens in field sites for later determination of lymphocyte subset percentages, which are commonly assessed in immunodeficient and cancer patients.

Use of total lymphocyte count for monitoring response to antiretroviral therapy

The CD4 cell count has become a key laboratory measurement in the management of human immunodeficiency virus (HIV) disease. In ideal situations, HIV-infected persons are followed up longitudinally with serial CD4 cell counts to determine disease progression, risk for opportunistic infection, and the need for prophylactic or therapeutic intervention. However, the use of the CD4 cell count in resource-limited settings is often not possible because of lack of availability and high cost. Thus, other laboratory markers have been proposed as substitutes for the CD4 cell count. The data regarding the clinical utility of the total lymphocyte count (TLC) as a potential surrogate marker of immune function in patients with HIV disease are examined. The role of the TLC in the initiation of antiretroviral therapy and opportunistic infection prophylaxis, as well as the role of the TLC in monitoring the response to antiretroviral therapy, are also addressed.

Successful implementation of a low-cost method for enumerating CD4+ T lymphocytes in resource-limited settings: the ANRS 12-26 study

OBJECTIVE

To evaluate the feasibility and the relevance of the implementation of an alternative technique to flow cytometry (FC) for enumerating CD4 T cells (Dynabeads; Dynal Biotech, Oslo, Norway), based on quantifying CD4 T cells by epifluorescent microscopy following their isolation using anti-CD4 monoclonal antibody-coated magnetic beads.

DESIGN

International multi-center study. Five consecutive runs of dual CD4 T-lymphocyte enumeration by both techniques in six sites in five countries of West Africa.

METHODS

A total of 657 pairs of values of CD4 cell counts were generated by 43 technicians by both FC (TruCount; Becton Dickinson Immunocytometry Systems, San Jose, California, USA) and Dynabeads from blood samples obtained from 301 HIV-infected patients, seen in one (n = 112), two (n = 61), three (n = 75), four (n = 40) or five (n = 13) occasions.

RESULTS

The correlation coefficient between the results of the two techniques was 0.89. The overall systematic difference between Dynabeads and FC was -16 x 10(6) cells/l (P < 10(-4)). The median difference was insignificant (+7.5 cells) for CD4 cell counts below 200 x 10(6) cells/l and increased with CD4 levels. Patients were consistently classified at the threshold of 200 x 106 cells/l by both methods in 88.7% of cases. Among the 74 discrepant pairs of values, only 31 (4.7%) exhibited a difference of more than 100 x 10(6) cells/l.

CONCLUSIONS

Results from Dynabeads and FC were highly correlated. The ability of the alternative method to consistently classify results in agreement with FC, at thresholds of CD4 cell counts relevant for clinical care, was high. The implementation of this low-cost method was easy and successful in the West African context.

Socio-economic and health characteristics of HIV-infected patients seeking care in relation to access to the Drug Access Initiative and to antiretroviral treatment in Côte d'Ivoire

OBJECTIVE

To compare socio-economic and health characteristics of HIV-infected patients in Côte d'Ivoire whether or not they had access to the Drug Access Initiative (DAI) and to antiretroviral drug (ARV) treatment.

DESIGN AND METHODS

Cross-sectional survey using medical files, blood sampling for CD4 cell counts and face-to-face interviews among all patients, informed of their HIV status, who attended during a 6-week period in the five DAI referral centres and three additional centres in charge of HIV care in Abidjan and Bouaké (participation rate = 65.4%). Multiple logistic regression using generalized estimating equations (GEE) to identify factors related to non-access to DAI and to ARV treatment.

RESULTS

Among the 711 respondents, 23.0% were ARV-treated, 14.2% had been included in the DAI but were still waiting for initiation of ARV, and 62.7% were neither part of the DAI nor ARV-treated. In this latter group, less than one-third (29.6%) declared that they knew about the existence of the DAI. Among the 164 ARV-treated patients, 59.1% had benefited from DAI public subsidies partially covering the costs of drugs. In the non-DAI-non-ARV-treated group, 86% could have qualified for ARV treatment according to the DAI medical criteria (CD4 cell counts < 500 x 10(6) cells/l), and only 32.9% of those medically eligible were prescribed cotrimoxazole prophylaxis. In multivariate analysis, not being in the DAI and not being ARV-treated was related to: being a male, not having health care insurance, having a low level of education, living in poor housing conditions (absence of refrigerator in the household, absence of ventilation in patient's bedroom), and not being under cotrimoxazole prophylaxis.

CONCLUSION

The Ivoirian DAI has facilitated access to ARV treatment for a significant number of patients with limited ability to pay. The majority of HIV-infected patients seeking care however face persisting socio-economic and informational barriers to access to these treatments.

Affordable CD4(+)-T-cell counting by flow cytometry: CD45 gating for volumetric analysis

The flow cytometers that are currently supported by industry provide accurate CD4(+)-T-cell counts for monitoring human immunodeficiency virus disease but remain unaffordable for routine service work under resource-poor conditions. We therefore combined volumetric flow cytometry (measuring absolute lymphocyte counts in unit volumes of blood) and simpler protocols with generic monoclonal antibodies (MAbs) to increase cost efficiency. Volumetric absolute counts were generated using CD45/CD4 and CD45/CD8 MAb combinations in two parallel tubes. The percentage values for the various subsets were also determined within the leukocyte and lymphocyte populations utilizing a fully automated protocol. The levels of agreement between the newly developed method and the present industry standards, including both volumetric and bead-based systems using a full MAb panel for subset analysis, were tested by Bland-Altman analyses. The limits of agreement for CD4 counts generated by the volumetric methods using either CD45/CD4 (in a single tube) or the full Trio MAb panel (in three tubes) on the CytoronAbsolute flow cytometer were between -29 and +46 cells/mm(3) with very little bias for CD4 counts (in favor of the Trio method: +8 CD4(+) lymphocytes/mm(3); 0.38% of lymphocytes). The limits of agreement for absolute CD4 counts yielded by the volumetric CD45/CD4 method and the bead-based method were between -118 and +98 cells/mm(3), again with a negligible bias (-10 CD4(+) lymphocytes/mm(3)). In the volumetric method using CD45/CD8, the strongly CD8(+) cells were gated and the levels of agreement with the full Trio showed a minor bias (in favor of the Trio; +40 CD8(+) cells/mm(3); 5.2% of lymphocytes) without a significant influence on CD4/CD8 ratios. One trained flow cytometrist was able to process 300 to 400 stained tubes per day. This workload extrapolates to a throughput of >30,000 samples per year if both CD45/CD4 and CD45/CD8 stainings are performed for each patient or a throughput of >60,000 samples if only CD45/CD4 counts are tested in a single tube. Thus, on the basis of the high efficiency and excellent agreement with the present industry standards, volumetric flow cytometers with automated gating protocols and autobiosamplers, complemented by generic CD45, CD4, and CD8 MAbs used in two-color immunofluorescence, represent the most suitable arrangements for large regional laboratories in resource-poor settings.

Stabilised cellular immuno-fluorescence assay: CD45 expression as a calibration standard for human leukocytes

We first confirmed the precision of the quantitative indirect immunofluorescence (QIFI) test by demonstrating that blood lymphocytes from different individuals expressed CD45 leucocyte antigens at a very similar level (mean: 201 x 10(3) antibody binding capacity (ABC)/lymphocyte) with only minimal variation (CV% 2.5%). These values were maintained for 4 days in blood samples when kept at 20 degrees C, and for up to 14 days in samples fixed with TransFix. Using long-term stabilisation, after an initial drop of 10-15% the CD45 ABC/lymphocyte values remained stable at an 85-90% level for >1 year. These biological standards were used to check other quantitative IF techniques. The quantum simply cellular (QSC) method showed variable results (85-240%), and the QuantiBRITE method gave values as low as 30-40% of the expected values, indicating that biological standards such as CD45 ABC/lymphocytes are absolutely essential to check the performance of methods that claim to quantify immunofluorescence (IF). Next, these standards were used to establish the stabilised cellular immuno-fluorescence assay (SCIFA) as follows. The ABC x 10(3)/cell values established by QIFI on leucocyte populations such as lympho-, mono- and granulocytes were used to create calibration curves for the CD45 antigen and its isoforms CD45RA, -R0 and -RB. The same cell populations were then stained with monoclonal antibodies (MAbs) directly conjugated to different fluorochromes in order to translate the mean fluorescence intensity (MFI) values seen with the directly labelled reagents to values of ABCx10(3)/cells. Using SCIFA with a triple-colour direct IF, the display of CD45 and its isoforms were quantitated on the 'virgin' or 'unprimed' (CD45RA+) and 'primed' (CD45R0+) subsets in both the CD4+ and CD8+ T cell lineages. We also observed that the CD4+ and CD8+ T cells in transit between the 'virgin' and 'primed' subsets frequently displayed different levels of the CD45RA and -R0 molecules, pointing to the physiological variability of the CD45RA-R0 switching process. In conclusion, internal biological standards, with known stable expression of ABC/cell, should be used to evaluate IF staining patterns in a quantitative manner during routine investigations.

Precise CD4 T-cell counting using red diode laser excitation: for richer, for poorer

BACKGROUND

Measuring CD4 T-cell counts at low cost is relevant in dealing with the human immunodeficiency virus (HIV) epidemic throughout the developing world. The recently introduced novel concepts in gating strategies and sample stabilization facilitate affordable immunophenotyping by flow cytometry. However, the impact of these developments is still limited by the high cost of currently available flow cytometers.

METHODS

Diode lasers emitting 10-15 mW at 635 nm are one-tenth the size and cost and require one thousandth the power of an equivalent 488-nm argon ion laser. We used the available 635-nm diode-based flow cytometers, including PA-II, Luminex 100, SuperMot, and FACSCalibur, to investigate whether these instruments can generate reliable CD4 counts when used with allophycocyanin (APC) and cyanin-5 (Cy5)-labeled CD4 antibodies.

RESULTS

We document the feasibility of obtaining leucocyte differential counts using orthogonal side scatter (SSC) without the need for forward scatter (FSC). Accurate CD4% values among lymphocytes and leucocytes can be obtained by primary CD4 gating using a single CD4 monoclonal antibody conjugated to APC or Cy5. Double immunofluorescence (IF) staining with CD4-APC (FL1) and CD45-APC-Cy7 (FL2) introduces pan-leucogating for a convenient assessment of absolute CD4 counts on double platforms. We demonstrate that small flow cytometers with laser diodes are capable of delivering absolute CD4 T-cell counts with a precision similar to the performance of the current state-of-the-art single-platform instruments (e.g., the CytoronAbsolute; R(2) = 0.961). In this respect, they appear to be superior to the nonflow CD4 counting techniques.

CONCLUSIONS

Accurate CD4 counts can be generated at minimal cost on red diode laser-operated flow cytometers, retaining the potential for high throughput capacity without compromising precision. With further improvements in volumetric technology and clinical software, these cytometers may develop into a new generation of inexpensive battery-operated laboratory hardware that combines cellular phenotyping with bead-based multiplexing immunoassays for (HIV) serology.