External quality assessment of flow cytometric HLA-B27 typing

Human HLA-B27 typing using the BD™ HLA-B27 kit on the BD FACSVia™ system: A multicenter study

The BD FACSVia™ system is a novel flow cytometer with improved workflow efficiencies. To evaluate the HLA‐B27 application developed on the BD FACSVia system utilizing the BD™ HLA‐B27 kit, we conducted a concordance study at three centers to compare with the BD FACSCalibur™ system. Prepared donor samples (n = 594) were analyzed on both the BD FACSVia and BD FACSCalibur for the HLA‐B27 assay. Adjudication of HLA‐B27 discordant results was performed using the reverse sequence‐specific oligonucleotide (rSSO) DNA typing method (LABType® SSO, One Lambda). On the BD FACSVia system 80 B27 positive, 499 B27 negative and 15 “Inconclusive” samples were observed. The corresponding BD FACSCalibur results were 73 B27 positive, 502 B27 negative and 19 “gray zone” samples. The overall concordance of HLA‐B27 determination was 98% between the two systems with seven more positives identified on BD FACSVia as compared to BD FACSCalibur. The equivocal zone between positive and negative on BD FACSVia (named “Inconclusive”) and on BD FACSCalibur (named “gray zone”) is due to antibody cross reactivity of HLA‐B27 clone GS145.2. One negative sample verified with the rSSO DNA method was reported as HLA‐B27 positive by the BD FACSVia system leading to a false positive result. Our study demonstrated concordance results between the BD FACSVia system and BD FACSCalibur. Intersite reproducibility of BD HLA‐B27 assay remained within the limits of acceptability. © 2018 The Authors. Cytometry Part B: Clinical Cytometry published by Wiley Periodicals, Inc. on behalf of International Clinical Cytometry Society

HLA-B27 testing: A journey from flow cytometry to molecular subtyping

BACKGROUND

Determination of HLA-B27 status plays an important role as adjuvant in suspected cases for diagnosis of Ankylosing Spondilytis (AS). Objectives of this study were to evaluate (i) flow cytometry method in comparison with DNA microarray for HLA-B27 typing and (ii) EUROArray HLA-B27 Direct assay for HLA-B27 allele detection along with discrimination of AS/non-AS subtypes in Indian population.

METHODS

A total of 7543 patients with a presumptive clinical diagnosis of AS were referred for screening of HLA-B27. All samples were initially tested by flow cytometry, and based on its findings, 1560 samples were analyzed for the presence of HLA-B27 allele by microarray technology. A subset of samples (n = 200) were further tested by DNA sequencing for identification of HLA-B27 subtypes.

RESULTS

Screening of HLA-B27 by flow cytometry reported 1551 positive (20.56%) and 5556 negative (73.65%) cases. Remaining 436 (5.78%) samples were identified within equivocal zone. Of cases (n = 1560) analyzed by microarray method, 1333 (85.44%) and 227 (14.55%) were detected microarray positive and negative, respectively. DNA sequencing identified HLA-B*27:07 as the predominant subtype among cases showing ex2 positivity by microarray method. Of 200 cases, 20 cases (14 of HLA-B*07 and 6 of HLA-B*37) of HLA-B27 cross-reactive subtypes were also identified.

CONCLUSION

We recommend DNA typing as a complementary tool along with flow cytometry to accomplish successful HLA-B27 phenotype determination. This is the first study among Indian population to evaluate efficacy of EUROArray to detect B27 allele and its potential to indicate the presence of nondisease-associated alleles in Indian population.

One-tube HLA-B27/B2708 typing by flow cytometry using two "Anti-HLA-B27" monoclonal antibody reagents

BACKGROUND

Flow cytometry-based methods are widely used to detect the ankylosing spondylitis-associated HLA-B27/B2708 antigens. However, the generally used "HLA-B27" monoclonal antibodies (moabs) cross-react with many HLA specificities, including the common HLA-B7 antigen. Thus, using two "B27" moabs is highly recommended.

METHODS

The assay used two "HLA-B27" reagents, FITC and PE conjugated, respectively and a PE-Cy5 anti-CD3 antibody. Assay verification used 51 reference subjects possessing B*2705, B*2702, and B*2708 and a range of cross-reactive HLA antigens. A total of 1,006 consecutive patients' samples, referred for "HLA-B27 typing", were assayed alongside our standard flow cytometry method. A further 12 low frequency HLA-B*27 specificities were tested. Samples reacting with one "B27" moab only were B*27 allele typed by PCR using sequence-specific primers.

RESULTS

All patient B27/B2708 positives (28.3%) were identified by our one-tube method which detected B*2705, B*2702, B*2708, and 8/12 other B*27 specificities. It was unaffected by HLA-B7 and other cross-reactive antigens but required a minor adjustment, a reduction in the volume of one of the "B27" moabs used, to avoid detecting a minority of HLA-B57 subjects.

CONCLUSIONS

Our one-tube B27/B2708 assay is simple, robust, uses two "B27" moabs for typing precision and security, does not suffer from interference by HLA-B7 or other cross-reactive antigens and has the obvious advantage of using a single tube per typing.

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.

Evaluation of a method for monoclonal antibody HLA-B27 analysis with the CELL-DYN Sapphire haematology analyser

Analysis of HLA-B27 is usually performed by flow cytometry using commercial single or two colour fluorescence reagents. The CELL-DYN Sapphire (CD-Sapphire) is a high-volume routine haematology analyser that allows cell population analysis by monoclonal antibody fluorochromes analogous to flow cytometry. In this study, in-house flow cytometry analysis (n = 96, HLA-B27, One Lambda) performed on routine patient samples was used as the comparison method for analysis of HLA-B27, One Lambda (n = 40) and HLA-B27/HLA-B7, Immunotech (n = 96) reagents on the CD-Sapphire. The One Lambda results agreed 100% with the comparison method and offered clear population discrimination. The Immunotech combination also had a high level of agreement, but interpretation was more complex because of the wider cross-reactivity of the ABC-m3 antibody with B7 and other HLA-B alleles. When analysing HLA-B27 with antibodies showing nonspecific reactivity, a cut-off staining level yielding high specificity should be chosen, as the primary diagnostic value of HLA-B27 is as a 'rule-out' test for ankylosing spondylitis. The CD-Sapphire incorporates automated sampling and lysis, and medical scientists familiar with the instrument would require little additional technical training to perform the analysis. The reduced preanalytical work and total turnaround time constitute an important step towards automation of HLA-B27 and similar simple high-volume flow cytometry analysis.

External Quality Assessment of HLA-B*5701 Reporting: An International Multicentre Survey

Objectives

HLA-B*5701 strongly predicts abacavir hypersensitivity (HSR), but implementation of effective routine screening into clinical practice requires testing be practical and accurate. We tested the proficiency of HLA-B*5701 typing among laboratories using sequence-specific primer PCR.

Design and methods

DNA panels (1 and 2) were distributed to seven laboratories (A to G) for blinded typing of the HLA-B*5701 allele. Panel 1 ( n=10 samples; n=7 laboratories) included 3 positives and other closely related B17 subtypes (B*5702, B*5703, B*5704 and B*5801). Panel 2 ( n=96 samples; n=4 laboratories) included 36 positives among a broad spectrum of other B alleles. Two laboratories (A and B) also submitted 96 routine samples, typed by the same methodology, to the reference centre for additional analysis by sequence-based typing.

Results

All laboratories correctly typed panel 1 for HLA-B*5701 carriage. Laboratories A, B and C identified HLA-B*5701 alleles in panel 2 with 100% sensitivity and 100% specificity. Laboratory D reported one false negative, reportedly due to a sampling error. The results obtained for routine samples typed by laboratories A and B and those generated by the reference laboratory using sequencing were fully concordant.

Conclusions

Detection of HLA-B*5701 alleles among laboratories was 100% specific and 99.4% sensitive, indicating that participating HIV testing laboratories were currently offering effective primary screening to identify individuals at high risk of abacavir HSR. Accurate reporting of HLA-B*5701 status is critical for the safe administration of this drug and participation in quality assurance programmes by all sites who report HLA-B*5701 status should be promoted.

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

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

HLA-B27 genotyping by Fluorescent Resonance Emission Transfer (FRET) probes in real-time PCR

Several polymerase chain reaction (PCR)-based human leukocyte antigen (HLA) genotyping methods are in use, but none is fully satisfactory. The introduction of real-time PCR (rt-PCR) with fluorescence resonance energy transfer (FRET) probes provides a powerful tool to overcome the drawbacks of current methods such as the long processing time and the requirement for post-PCR manual procedures. Here we present evidence that the FRET-fluorotyping principle may resolve HLA-B27 variants, providing a higher resolution in less time than the techniques currently in use. The protocol uses between one and three consecutive amplification reactions depending on the resolution required. The first reaction, aimed at detecting HLA-B27-positive samples, uses beta-globin coamplification as control. The second reaction, aimed at resolving most frequent B27 alleles, uses two hybridization probes whose melting temperatures curves allow the classification of HLA-B27 alleles into eight groups. By adding a third reaction, even the rarest alleles associated and not associated to ankylosing spondylitis (AS) may be discriminated. The technique was blindly tested on 60 samples from individuals previously typed and confirmed by standard PCR sequence-specific oligoprobes-PCR sequence and PCR-based typing PCR-SBT (30 B27+, 30 non-B27). There was a complete concordance rate, thus confirming the potential of this new technique for clinical HLA-B27 typing and for HLA typing in general.

An evaluation of Com-B27, a fluorescein-conjugated mouse anti-HLA-B27 reagent

We evaluated the HLA-B27 typing reagent Com-B27, which is claimed to show minimal cross-reactivity with HLA-B7, for use in flow cytometry-based typing. This combination reagent consists of the fluorescein-conjugated HLA-B27 mouse monoclonal antibody ABC-m3 and a non-conjugated HLA-B7 monoclonal antibody that is claimed to block the reactivity of ABC-m3 to B7 without affecting its reactivity to B27. It reacted well with B27 (B*2702, B*2705) and B2708 [mean median channel fluorescence intensity (MCFI) 8.40] and weakly with B7 (including cells from homozygous B*07 donors), B42/B73 and B22/B37/B44 reference cells (mean MCFI 2.05, 3.09 and 1.10, respectively). It showed a uniform discrimination between B7 and B27/B2708 with no 'overlap' in MCFI values, which was seen with the standard ABC-m3 antibody. There was complete agreement when our standard three-antibody-based B27/B2708 flow cytometry assay and the Com-B27 reagent alone were used to independently assign B27/B2708 status to 651 random patients. Thus, the Com-B27 reagent provided improved discrimination between B7 and B27/B2708 over the ABC-m3 antibody, and its B27/B2708 assignments were comparable with our standard flow cytometry assay. However, for consistently reliable B27/B2708 typing we continue to recommend the use of a minimum of two B27 reagents in a protocol that includes DNA-based testing of 'equivocal' B27/B2708 assignments.

Flow cytometric HLA-B27 screening: cross-reactivity patterns of commercially available anti-HLA-B27 monoclonal antibodies with other HLA-B antigens

BACKGROUND

Some 50 clinical laboratories in the Benelux perform flow cytometric HLA-B27 screening and participate in the Benelux external quality assessment scheme operational since 1995. Results from this scheme indicate that cross-reactivity of HLA-B27 monoclonal antibodies (mAbs) is a major problem.

METHODS

We analyzed cross-reactivity patterns of commercially available mAbs for HLA-B27 screening. Three clones of HLA-B27 mAb (ABC-m3, n = 3; FD705; and GS145.2) from five manufacturers were evaluated. Test cells were selected as to express HLA-B antigens with known serologic cross-reactions (HLA-B7, B12, B13, B16, B17, B22, B37, B40, B41, B42, B47, and B48). Cells without B27 cross-reactive antigens (B5, B8, B14, B15, B21, and B35) and cells positive for B27 were included as controls. All tests were performed and interpreted as recommended by the manufacturers. Cross-reactivity was defined as increased fluorescence intensity in comparison with the baseline reactivity observed with the corresponding immunoglobulin G isotype control mAb.

RESULTS AND CONCLUSIONS

All mAbs tested showed cross-reactivity, ranging from weak (+/-) to strong (+), with different antigens and different degrees of intensity-ABC-m3: (+/-) B12, B16, B17, B41, B47, and B48 and (+) B7, B13, B22, B37, B40, and B42; GS145.2: (+/-) B13, B17, B22, B40, and B47 and (+) B7, B16, B37, B42, and B48; FD705: (+/-) B12, B13, B16, and B48 and (+) B17, B37, and B47. If one mAb had been used for HLA-B27 screening, ABC-m3 would have yielded nine false-positive B27 assignments, FD705 would have yielded seven, and GS145.2 would have yielded two. This problem largely canbe avoided by the combined use of two different mAb clones. The combination of FD705 and GS145.2 yielded the best results, with one false-positive HLA-B27 assignment among the 99 HLA-B27(-) samples of this highly selected panel.