A multicolor, no-lyse no-wash assay for the absolute counting of CD34+ cells by flow cytometry

4-Color Flow Cytometric Crossmatch Using Whole Blood Lysis

BACKGROUND

In lymphocyte crossmatch using flow cytometry (flow cytometric crossmatch, FCXM), the conventional tricolor FCXM protocol requires a mononuclear cell isolation step. To develop a new, more streamlined protocol, we introduced whole blood lysis (WBL) and CD45 fluorescence-triggered acquisition using 4-color flow cytometry.

METHODS

A total of 186 donor/recipient pairs for transplantation were classified into donor-specific human leukocyte antigen (HLA) alloantibody-positive (DSA+, n = 78) and DSA-negative (DSA-, n = 108) groups. The latter group was reclassified into blood group ABO-incompatible (ABOi, n = 56) and ABO-compatible (n = 52) subgroups. The WBL FCXM protocol with CD45 V500-C was optimized using a FACSLyric cytometer (BD Biosciences) with 3 lasers. Measurements for T cells or B cells were calculated as a mean fluorescence intensity (MFI) ratio (test divided by control). WBL FCXM was compared with conventional FCXM in each group.

RESULTS

WBL FCXM showed no difference quantitatively compared with conventional FCXM, except for the B cell FCXM in the DSA- group (B cell MFI ratio: 1.06 ± 0.44 and 0.92 ± 0.41, respectively [P = .0001]). There was no ABO antibody interference in the ABOi subgroup. Similar results were observed in the qualitative determinations of FCXM as follows: 1) In the DSA+ group, the sensitivity of B cell WBL FCXM (96.2%) showed no difference compared with that of conventional FCXM (91.0%, P = .2188) and 2) In the DSA- group, the specificity of T cell WBL FCXM (96.3%) showed no difference compared with that of conventional FCXM (98.1%, P = .6250). WBL FCXM reduced the turnaround time by 50 min compared with that by conventional FCXM.

CONCLUSIONS

WBL FCXM demonstrated comparable assay performance to that of conventional FCXM. Because this new FCXM protocol is simple and does not compromise assay sensitivity, it has the potential to replace the conventional method in histocompatibility laboratory settings.

Flow-cytometry-based protocols for human blood/marrow immunophenotyping with minimal sample perturbation

This protocol provides instructions to improve flow cytometry analysis of marrow/peripheral blood cells by avoiding erythrolytic solutions, density gradients, and washing steps. We describe two basic approaches for identifying cell surface antigens with minimal sample perturbation, which have been successfully used to identify healthy and pathologically rare cells. The greatest advantage of these approaches is that they minimize the unwanted effect caused by sample preparation, allowing for improved study of live cells at the point of analysis.

For complete details on the use and execution of this protocol, please refer to Petriz et al. (2018).

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Optimized protocol to identify cell surface antigens with minimal sample perturbation

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Efficient identification of target cells avoiding artifacts from erythrolytic solutions

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Suitable for the simultaneous phenotypic and functional analysis of blood/marrow cells

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Detailed gating strategies to discriminate nucleated from non- nucleated cells

The effect of erythrocyte lysing reagents on enumeration of leukocyte subpopulations compared with a no-lyse-no-wash protocol

INTRODUCTION

Standard protocols in flow cytometry (FCM) require lysis of erythrocytes, which may induce an unwanted loss of leukocytes as bystander effect.

METHODS

In the present study, we investigated the influence of 6 laboratory protocols using 4 different lysing reagents, FACS^® Lysing Solution (FacsL), QUICKLYSIS^® (QuickL), IOTest^® 3 Lysing Solution (NH4Cl), VersaLyse^® (VersaL), and VersaLyse^® with added fixative (VersaFix) on the relative quantity of leukocyte subsets identified by CD3, CD4, CD8, CD19, CD14, CD16, CD56, and CD45, applying a no-lyse-no-wash (NoL) protocol as reference. In addition, we compared the efficiency of red blood cell (RBC) lysis.

RESULTS

Peripheral blood samples from 52 individuals were analyzed. NoL was suitable as reference method, but led to less clear-cut gating of lymphocyte and monocyte populations due to a wider distribution of light scatter. Best completeness of RBC lysis with remaining erythrocytes below 10% was achieved using NH4Cl and VersaL. We observed a loss of 11% of monocytes after QuickL. Lymphocyte counts were 19% lower after FacsL. Cell subsets within the lymphocyte compartment were rather similar between the different methods with the exception of lower B-cell counts (-8%) and higher NK-cell counts (+11%) after FacsL. NH4Cl and VersaL were in good accordance with the NoL method and also with the mean values of all methods.

CONCLUSION

Our data show that the lysing reagents tested lead to specific deviations in the quantitation of leukocyte subsets and show different efficiency of erythrocyte lysis.

Overcoming the deceptively low viability of CD45+ cells in thawed cord blood unit segments

BACKGROUND AND OBJECTIVES

There is no standard methodology for post-thaw sample preparation for viability analysis of umbilical cord blood units (CBU). A common challenge faced by CB bank is for their product to meet the post-thaw cell viability threshold for CD45⁺ cells set at 40% by NetCord-FACT. The objective of this work was to improve the post-thaw staining method to maximize CD45⁺ cell viability so that clinically valuable samples meet the NetCord-FACT threshold criteria for CD45⁺ and CD34⁺ cell viabilities.

MATERIALS AND METHODS

Samples of CBU buffy coats and CBU segments were thawed and taken for staining. Various parameters were evaluated on CD45⁺ and CD34⁺ cell viability as measured by 7-actinomycin D (7-AAD) staining.

RESULTS

The results revealed that initiating the staining at 20 min post-thaw instead of 30, shortening the red cell lysis treatment, or performing lysis on ice and removing this step all together, all improved the viability of CD45⁺ cells. Using CBU segments, it was shown that the most effective approach in increasing the viability of CD45⁺ cells was the complete omission of red cell lysis step. However, removal of the lysis step can create technical artefacts during flow cytometry acquisition that results in an underestimation of the viability of CD34⁺ cells. This can be avoided and CD34⁺ cell viability restored with additional thresholding on CD45 signal.

CONCLUSION

CB CD45⁺ cells are sensitive to red cell lysis treatment post-thaw; omission of this step provides the best viability and ultimately better reflects the quality of cells used for transplantation.

Collection, Storage, and Preparation of Human Blood Cells

Human peripheral blood is often studied by flow cytometry in both the research and clinical laboratories. The methods for collection, storage, and preparation of peripheral blood will vary depending on the cell lineage to be examined as well as the type of assay to be performed. This unit presents protocols for collection of blood, separation of leukocytes from whole blood by lysis of erythrocytes, isolating mononuclear cells by density gradient separation, and assorted non-flow sorting methods, such as magnetic bead separations, for enriching specific cell populations, including monocytes, T lymphocytes, B lymphocytes, neutrophils, and platelets, prior to flow cytometric analysis. A protocol is also offered for cryopreservation of cells, since clinical research often involves retrospective flow cytometric analysis of samples stored over a period of months or years.

Clinical, immunological and treatment-related factors associated with normalised CD4+/CD8+ T-cell ratio: effect of naïve and memory T-cell subsets

Background

Although effective antiretroviral therapy(ART) increases CD4+ T-cell count, responses to ART vary considerably and only a minority of patients normalise their CD4+/CD8+ ratio. Although retention of naïve CD4+ T-cells is thought to predict better immune responses, relationships between CD4+ and CD8+ T-cell subsets and CD4+/CD8+ ratio have not been well described.

Methods

A cross-sectional study in a cohort of ambulatory HIV+ patients. We used flow cytometry on fresh blood to determine expanded CD4+ and CD8+ T-cell subsets; CD45RO+CD62L+(central memory), CD45RO+CD62L-(effector memory) and CD45RO-CD62L+(naïve) alongside routine T-cell subsets(absolute, percentage CD4+ and CD8+ counts), HIVRNA and collected demographic and treatment data. Relationship between CD4+/CD8+ T-cell ratio and expanded T-cell subsets was determined using linear regression analysis. Results are median[IQR] and regression coefficients unless stated.

Results

We recruited 190 subjects, age 42(36–48) years, 65% male, 65.3% Caucasian, 91% on ART(52.6% on protease inhibitors), 78.4% with HIVRNA<40cps/ml and median ART duration 6.8(2.6–10.2) years. Nadir and current CD4+ counts were 200(112–309) and 465(335–607) cells/mm³ respectively. Median CD4+/CD8+ ratio was 0.6(0.4–1.0), with 26.3% of subjects achieving CD4+/CD8+ ratio>1. Of the expanded CD4+ T-cell subsets, 27.3(18.0–38.3)% were naïve, 36.8(29.0–40.0)% central memory and 27.4(20.0–38.5)% effector memory. Of the CD8+ T-cells subsets, 16.5(10.2–25.5)% were naïve, 19.9(12.7–26.6)% central memory and 41.0(31.8–52.5)% effector memory. In the multivariable adjusted analysis, total cumulative-ART exposure(+0.15,p = 0.007), higher nadir CD4+ count(+0.011,p<0.001) and higher %CD8+ naive T-cells(+0.0085,p<0.001) were associated with higher CD4+/CD8+ ratio, higher absolute CD8+ T-cell(-0.0044,p<0.001) and higher %CD4+ effector memory T-cells(-0.004,p = 0.0036) were associated with lower CD4+/CD8+ ratio. Those with CD4+/CD8+ ratio>1 had significantly higher median %CD8+ naive T-cells; 25.4(14.0–36.0)% versus 14.4(9.4–21.6)%, p<0.0001, but significantly lower absolute CD8+ count; 464(384.5–567) versus 765(603–1084) cells/mm³, p<0.001.

Conclusions

Study suggests important role for naïve CD8+ T-cell populations in normalisation of the immune response to HIV-infection. How these findings relate to persistent immune activation on ART requires further study.

Validation of cell-based fluorescence assays: practice guidelines from the ICSH and ICCS - part III - analytical issues

Clinical diagnostic assays, may be classified as quantitative, quasi-quantitative or qualitative. The assay's description should state what the assay needs to accomplish (intended use or purpose) and what it is not intended to achieve. The type(s) of samples (whole blood, peripheral blood mononuclear cells (PBMC), bone marrow, bone marrow mononuclear cells (BMMC), tissue, fine needle aspirate, fluid, etc.), instrument platform for use and anticoagulant restrictions should be fully validated for stability requirements and specified. When applicable, assay sensitivity and specificity should be fully validated and reported; these performance criteria will dictate the number and complexity of specimen samples required for validation. Assay processing and staining conditions (lyse/wash/fix/perm, stain pre or post, time and temperature, sample stability, etc.) should be described in detail and fully validated.

Stepwise optimization of the procedure for assessment of circulating progenitor cells in patients with myocardial infarction

BACKGROUND

The number and functional activity of circulating progenitor cells (CPCs) is altered in diabetic patients. Furthermore, reduced CPC count has been shown to independently predict cardiovascular events. Validation of CPCs as a biomarker for cardiovascular risk stratification requires rigorous methodology. Before a standard operation protocol (SOP) can be designed for such a trial, a variety of technical issues have to be addressed fundamentally, which include the appropriate type of red blood cell lysis buffer, FMO or isotype controls to identify rare cell populations from background noise, optimal antibody dilutions and conditions of sample storage. We herein propose improvements in critical steps of CPC isolation, antigenic characterization and determination of functional competence for final application in a prospective investigation of CPCs as a biomarker of outcome following acute myocardial infarction.

METHODS AND FINDINGS

In this validation study, we refined the standard operating procedure (SOP) for flow cytometry characterisation and functional analysis of CPCs from the first 18 patients of the Progenitor Cell Response after Myocardial Infarction Study (ProMIS). ProMIS aims to verify the prognostic value of CPCs in patients with either ST elevation or non-ST elevation myocardial infarction with or without diabetes mellitus, using cardiac magnetic resonance imaging (MRI) for assessment of ventricular function as a primary endpoint. Results indicate crucial steps for SOP implementation, namely timely cell isolation after sampling, use of appropriate lysis buffer to separate blood cell types and minimize the acquisition events during flow cytometry, adoption of proper fluorophore combination and antibody titration for multiple antigenic detection and introduction of counting beads for precise quantification of functional CPC activity in migration assay.

CONCLUSION AND SIGNIFICANCE

With systematic specification of factors influencing the enumeration of CPC by flow cytometry, the abundance and migration capacity of CPCs can be correctly assessed. Adoption of validated SOP is essential for refined comparison of patients with different comorbidities in the analysis of risk stratification.

Basics of standardization and calibration in cytometry--a review

Standardization, calibration, and controls (negative and positive controls) are essential for quality assurance. Cytometers are capable of reliable and repeatable cellular analyses. However, a prerequisite is instrument calibration and standardized preanalytics. Calibration is often done by beads. Beads are available for different quality control applications, e.g. calibration of size and measuring scale, compensation, absolute cell counting, and laser alignment. Results can be standardized by converting MFI values into MESF or ABC values. Standardized data allow comparison of experiments over a long period of time and between different instruments and laboratories. Alterations in the sensitivity of the cytometer can be detected by routinely performing quality control. The process of quality assurance quantifies and helps manage the variance from the desired value. Results can thus be compared objectively with those of other laboratories. Standardization is the basis of cytometry and a prerequisite for obtaining reliable data.

[Experimental Application of Whole Blood Flow Cytometry to HLA Crossmatch for Renal Transplantation.]

BACKGROUND

The lymphocytes separated from whole blood are used in HLA flow cytometry crossmatch (FCXM) for renal transplantation. In this study, the methodology of whole blood flow cytometry was applied to FCXM, omitting lymphocyte separation step.

METHODS

In the 20 cases (including positive 5 cases) of T cell FCXM for renal transplantation, the standard assay using the separated mononuclear cells (MNC) was compared with the two variant assays using whole blood. In the latter assay, the donor whole blood was incubated with the excessive recipient serum. The red cells were lysed (lysed whole blood, LWB). Otherwise, instead of red cell lysis, the signals of T cells among whole blood (WB) were acquired using fluorescence triggering. The sample/negative control mean fluorescence intensity (MFI) ratio was calculated for the interpretation.

RESULTS

The MFI ratio of the 20 cases by MNC, LWB and WB assay were 4.9+/-8.1, 5.4+/-9.7 and 4.8+/-7.8, respectively. Both LWB and WB assay were not significantly different from MNC assay (P= 0.313, 0.831, respectively, paired t-test). The qualitative determinations were concordant in all cases, except for one case which was weakly positive with MFI ratio 2.2 by LWB assay.

CONCLUSIONS

The assays using whole blood were comparable to the standard assay in FCXM for renal transplantation. This study indirectly supports that the variant methods can be used reliably in the case of the MNC preparation erroneously mixed with other blood cells.

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

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

Assessment of neutrophil activation in whole blood by flow cytometry

Flow cytometry methods currently used for measuring neutrophil activation involve sample manipulation, which may result in cellular depletion and artifactual activation. To design a new methodology for measurement of neutrophil activation with minimal sample manipulation. Oxidative burst and CD 11b neutrophil expression were simultaneously assessed by a new no-lyse no-wash technique and a standard lyse-method in 10 pediatric patients with recurrent infections and two patients with chronic granulomatous disease (CGD). The new technique was based on nucleic acid staining to discriminate erythrocytes and debris without requiring physical separation. Both methods served equally to confirm or eliminate the diagnosis of CGD and leukocyte adhesion deficiency type 1. The values of baseline CD11b and oxidative burst obtained using the lysis method were significantly higher than those obtained by the no-lyse no-wash method. After activation, the lysis method resulted in higher neutrophil depletion (41%vs. 19%, P = 0.03). When compared with standard methods, neutrophil activation assessment by a no-lyse no-wash method resulted in lower neutrophil depletion and differences in oxidative burst and CD11b neutrophil values.

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.

High-grade loss of leukocytes and hematopoietic progenitor cells caused by erythrocyte-lysing procedures for flow cytometric analyses

All current-flow cytometric techniques use erythrocyte-lysing procedures before leukocyte analysis. We investigated the impact of four lysing procedures with different flow cytometric techniques on the loss of leukocytes and hematopoietic progenitor cells in blood samples. A total of 280 determinations out of 10 samples were measured by two flow cytometers (FCMs), using a FACS-Calibur (Becton Dickinson) and a particle-analyzing system (PAS) with a "true volumetric unit" (Partec). All samples were prepared with four different commercially available erythrocyte-lysing reagents (n = 10, respectively). CD34(+) cells were determined in relation to counted leukocytes with both FCMs (dual platform determinations, 2-PF). In addition, further immunologic and nuclear staining determinations of cells with and without erythrocyte-lysing procedures were performed in the "true volumetric unit" (single platform mode 1-PF) using the PAS system (n = 10, respectively). In the 2-PF mode, both systems showed identical results for CD34(+) cells (r = 0.997). The comparison of 1-PF and 2-PF modes with immunologic stainings revealed a mean decrease of 34.5% for absolute amounts of CD45(+) cells [in detail: Becton-Dickinson (BD) lysis 40%; Ortho Diagnostics (OD) lysis 31%; Uti lyse (UL) 38%; Cylyse (CL) 29%] and of 41.3% for absolute concentration of CD34(+) cells [in detail: BD lysis 45%; OD lysis 40%; UL lysis 45%; CL lysis 34%] by the lysing procedures. In contrast, the nuclear stainings revealed a mean leukocyte loss of only 5% for the nonlysed samples and of 12% for lysed samples. All investigated lysing procedures induced a large loss of leukocytes and progenitor cells, obviously due to cell membrane destruction as demonstrated for identical samples in the 1-PF and 2-PF modes by immunologic and nuclear staining methods.