Practical guidelines for the high-sensitivity detection and monitoring of paroxysmal nocturnal hemoglobinuria clones by flow cytometry

Flow cytometry-Recognizing unusual populations in leukemia and lymphoma diagnosis

Flow cytometry is an invaluable technology in the examination of blood, bone marrow, tissue and body fluids for the presence or absence of hematological disease. It is used in both diagnostic and follow-up testing, with an increasingly important role in the detection of very small residual disease populations (Minimal Residual Disease, MRD) However, flow cytometry immunophenotyping of leukemia and lymphoma is highly dependent on interpretation of results and with the increased complexity of 8-10 color instruments routinely used in clinical laboratories, knowledge of disease-defining populations is increasingly important as is recognizing normal and reactive patterns. This manuscript presents case studies with flow cytometric patterns encountered in routine screening of samples sent for leukemia and lymphoma immunophenotyping, focusing mainly on B-cell disorders which may be missed or incorrectly interpreted by the laboratory (including a hematopathologist) performing the test. Case studies are used to illustrate our laboratory's standardized approach to the interpretation of flow cytometric data. In addition to a standardized approach, these cases emphasize the importance of interpretative skills of technologist and hematopathologists in recognizing abnormal patterns in detecting hematological malignancies.

[The PIG-A gene as a new biomarker of mutagenesis: proof of concept and technical specifications]

Gene mutations are not directly detected by current genotoxicity assays and most of them need a cell culture step. The whole blood PIG-A assay consists in the detection of the mutation frequency within the PIG-A sentinel gene by identification of glycosyl-phosphatidyl-inositol (GPI-) deficient cells. PIG-A mutated/GPI-deficient cells can be detected by flow cytometry as they no longer express surface fluorescence for GPI-linked markers. The last researches have focused on cell enrichment techniques leading to increased throughput and sensitivity. The results of this new and promising biomarker of mutagenesis, performed in humans or rodents, are now available within 2 hours after blood collection.

Multicenter validation of a simplified method for paroxysmal nocturnal hemoglobinuria screening

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) diagnostic guidelines recommend single-tube five- to six-color or two-tube four-color assays. PNH clones are detectable in only a fraction of patients at risk, and screening for new PNH cases can be complex and expensive. In this multicenter study, we have validated a simplified, one-tube two-color FLAER-based assay suitable for PNH screening.

METHODS

Six laboratories received samples containing spiked PNH leukocyte clones to be analyzed in parallel with a common six-color cocktail (FLAER/CD24/CD45/CD64/CD15/CD14) and a simplified two-color mixture (FLAER/CD15), a shared calibration procedure, and a common analysis protocol. Replicate precision and sensitivity tests were performed on PNH patients, from undiluted to 1:10 000. Specificity tests were performed on normal donors to identify the possible sources of artifacts.

RESULTS

The performance comparison between six-color and two-color assays showed an excellent agreement for granulocyte PNH clones. Dilution experiments showed an accurate detectability down to 0.01% sensitivity level for granulocyte PNH clones and to 1% for monocytes. Specificity experiments disclosed that basophils and platelets can contaminate the monocyte gate and generate false PNH events.

CONCLUSIONS

A simplified two-color (FLAER/CD15) PNH screening test has been validated in a highly standardized multicenter study and proved feasible and effective in ongoing regional programs. Precision, sensitivity, and specificity of the simplified test for granulocytes were comparable to the more complex and expensive six-color assay and applicable for screening also in peripheral laboratories. The diagnostic confirmation of PNH should be always performed by a reference center using the established technique on all cell lineages.

Recent advances in understanding clonal haematopoiesis in aplastic anaemia

Acquired aplastic anaemia (AA) is an immune-mediated bone marrow failure disorder inextricably linked to clonal haematopoiesis. The majority of AA patients have somatic mutations and/or structural chromosomal abnormalities detected as early as at diagnosis. In contrast to other conditions linked to clonal haematopoiesis, the clonal signature of AA reflects its immune pathophysiology. The most common alterations are clonal expansions of cells lacking glycophosphotidylinositol-anchored proteins, loss of human leucocyte antigen alleles, and mutations in BCOR/BCORL1, ASXL1 and DNMT3A. Here, we present the current knowledge of clonal haematopoiesis in AA as it relates to aging, inherited bone marrow failure, and the grey-zone overlap of AA and myelodysplastic syndrome (MDS). We conclude by discussing the significance of clonal haematopoiesis both for improved diagnosis of AA, as well as for a more precise, personalized approach to prognostication of outcomes and therapy choices.

Management of thrombosis in paroxysmal nocturnal hemoglobinuria: a clinician's guide

Paroxysmal nocturnal haemoglobinuria (PNH), an ultra-orphan disease with a prevalence of 15.9 per million in Europe, is a life-threatening disorder, characterized by haemolysis, bone marrow failure and thrombosis. Patients with PNH prior to the availability of eculizumab had a median survival of between 10 and 22 years, with thrombosis accounting for 22-67% of deaths. 29-44% of patients had at least one thrombosis. This paper provides a clinician's guide to the diagnosis, management and complications of PNH, with an emphasis on thrombosis.

Technical advances in flow cytometry-based diagnosis and monitoring of paroxysmal nocturnal hemoglobinuria

Objective:

To discuss the implementation of technical advances in laboratory diagnosis and monitoring of paroxysmal nocturnal hemoglobinuria for validation of high-sensitivity flow cytometry protocols.

Methods:

A retrospective study based on analysis of laboratory data from 745 patient samples submitted to flow cytometry for diagnosis and/or monitoring of paroxysmal nocturnal hemoglobinuria.

Results:

Implementation of technical advances reduced test costs and improved flow cytometry resolution for paroxysmal nocturnal hemoglobinuria clone detection.

Conclusion:

High-sensitivity flow cytometry allowed more sensitive determination of paroxysmal nocturnal hemoglobinuria clone type and size, particularly in samples with small clones.

Objetivo:

Discutir as melhorias técnicas no diagnóstico e no acompanhamento laboratorial de hemoglobinúria paroxística noturna para a validação da técnica de citometria de fluxo de alta sensibilidade.

Métodos:

Estudo retrospectivo, que envolveu a análise de dados laboratoriais de 745 pacientes com hipótese diagnóstica e/ou acompanhamento de hemoglobinúria paroxística noturna por citometria de fluxo.

Resultados:

Os avanços técnicos não só reduziram o custo do ensaio, mas também melhoraram a identificação e a resolução da citometria de fluxo para a detecção de clone hemoglobinúria paroxística noturna.

Conclusão:

A citometria de fluxo de alta sensibilidade possibilitou a identificação do tipo e do tamanho de clone de hemoglobinúria paroxística noturna, especialmente em amostras com pequeno clone.

Diagnostic screening of paroxysmal nocturnal hemoglobinuria: Prospective multicentric evaluation of the current medical indications

BACKGROUND

Although consensus guidelines have been proposed in 2010 for the diagnostic screening of paroxysmal nocturnal hemoglobinuria (PNH) by flow cytometry (FCM), so far no study has investigated the efficiency of such medical indications in multicentric vs. reference laboratory settings.

METHODS

Here we evaluate the efficiency of consensus medical indications for PNH testing in 3,938 peripheral blood samples submitted to FCM testing in 24 laboratories in Spain and one reference center in Brazil.

RESULTS

Overall, diagnostic screening based on consensus medical indications was highly efficient (14% of PNH⁺ samples) both in the multicenter setting in Spain (10%) and the reference laboratory in Brazil (16%). The highest frequency of PNH⁺ cases was observed among patients screened because of bone marrow (BM) failure syndrome (33%), particularly among those with aplastic anemia (AA; 45%) and to a less extent also a myelodysplastic syndrome (MDS; 10%). Among the other individuals studied, the most efficient medical indications for PNH screening included: hemolytic anemia (19%), hemoglobinuria (48%) and unexplained cytopenias (9%). In contrast, only a minor fraction of the patients who had been submitted for PNH testing because of unexplained thrombosis in the absence of cytopenia, were positive (0.4%).

CONCLUSIONS

In summary, our results demonstrate that the current medical indications for PNH screening by FCM are highly efficient, although improved screening algorithms are needed for patients presenting with thrombosis and normal blood cell counts. © 2016 International Clinical Cytometry Society.

Expression pattern of CD55 and CD59 on red blood cells in sickle cell disease

OBJECTIVES

To investigate the pattern of CD55 and CD59 expression on RBCs of SCD patients, and its association with anemia, biochemical parameters of hemolysis, level of erythropoietin, and pro-inflammatory markers.

METHODS

Flow cytometric analysis was performed on RBCs from 71 adult SCD patients and 53 healthy controls, using the commercial REDQUANT kit.

RESULTS

CD59 deficiency was significantly higher among SCD patients than among healthy controls. The proportions of CD55-deficient and CD59-deficient RBCs from SCD patients were significantly higher when compared with those from healthy controls (0.17 vs. 0.09 and 2.1 vs. 1.2, respectively). The MFI of CD55 and CD59 expression on RBCs in SCD was significantly reduced when compared to the expression in healthy controls (5.2 vs. 6.4 and 19.4 vs 20.3, respectively). The pattern of CD55 and CD59 expression was not correlated with anemia, biomarkers of hemolysis, erythropoietin level, or other pro-inflammatory markers.

DISCUSSION

There is an altered pattern of CD55 and CD59 expression on RBCs of SCD Patients; however, it does not seem to play a causal role in the pathophysiology of anemia, and is unlikely to be influenced by the level of erythropoietin or other inflammatory mediators.

Minor populations of paroxysmal nocturnal hemoglobinuria-type cells in patients with chronic idiopathic neutropenia

Chronic idiopathic neutropenia (CIN) is an acquired disorder of granulopoiesis characterized by increased apoptosis of the bone marrow (BM) granulocytic progenitor cells under the influence of pro-inflammatory mediators and oligoclonal/monoclonal T-lymphocytes. Because patients with immune-mediated BM failure display frequently paroxysmal nocturnal hemoglobinuria (PNH)-type cells in the peripheral blood (PB), we investigated the possible existence of PNH-type cells in 91 patients with CIN using flow cytometry. The patients displayed increased proportions of PNH-type glycophorin A⁺ /CD59^dim and glycophorin A⁺ /CD59^- red blood cells (RBCs), FLAER^- /CD24^- granulocytes, and FLAER^- /CD14^- monocytes, compared to controls (n = 55). A positive correlation was found between the proportions of PNH-type RBCs, granulocytes, and monocytes and an inverse correlation between the number of PB neutrophils and the proportions of PNH-type cell populations. The number of patients, displaying percentages of PNH-type cells above the highest percentage observed in the control group, was significantly increased among patients with skewed compared to those with normal T-cell receptor repertoire suggesting that T-cell-mediated immune processes underlie the emergence of PNH-type cells in CIN. Our findings suggest that patients with CIN display PNH-type cells in the PB at a high frequency corroborating the hypothesis that CIN belongs to the immune-mediated BM failure syndromes.

Current international flow cytometric practices for the detection and monitoring of paroxysmal nocturnal haemoglobinuria clones: A UK NEQAS survey

BACKGROUND

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare acquired genetic disorder, with an incidence of approximately 1.3 new cases per million population per year. Evidence from the UK National External Quality Assessment Service for Leucocyte Immunophenotyping (UK NEQAS LI) programme suggested major discrepancies on how PNH testing is undertaken. To investigate this we surveyed laboratories in the UK NEQAS LI PNH programme and report here the findings.

METHODS

A questionnaire was distributed to all centres registered in UK NEQAS LI flow cytometry programmes (n = 1587). Comprising several subsections, it covered the majority of clinical flow cytometric practices. Participants completed a general section and then the subsections relevant to their laboratory repertoire. One subsection contained 34 questions regarding practices in PNH clone detection.

RESULTS

A total of 105 laboratories returned results for the PNH section; the results demonstrated lack of consensus in all areas of PNH testing. Variation was seen in gating and testing strategies, sensitivity levels and final reporting of test results. Several incorrect practices were highlighted such as inappropriate antibody selection and failure to wash the red blood cells (RBCs) prior to analysis.

CONCLUSION

Despite the availability of consensus guidelines there appears to be no agreement in the detection and monitoring of PNH. We found only fourteen centres using methods compatible with the International Clinical Cytometry Society guidelines. Of specific note we found that no two laboratories used the same method. This technical variation could lead to incorrect diagnoses, highlighting the need for better adoption and understanding of consensus practices. © 2016 International Clinical Cytometry Society.

Role of vitamin D receptor gene polymorphisms in aplastic anemia: a case-control study from China

INTRODUCTION

Vitamin D receptor (VDR) gene and its polymorphisms are highlighted as candidate components for susceptibility to various autoimmune diseases. The aim of this study was to investigate the role of VDR polymorphisms (rs2228570, rs1544410, rs7975232, and rs731236) in aplastic anemia (AA).

METHODS

In this case-control study, the genotyping of VDR rs1544410 (c.1024 + 283G>A), rs7975232 (c.1025-49G>T), and rs731236 (c.1056T>C) polymorphisms was conducted using polymerase chain reaction (PCR)-ligase detection reaction, while the genotyping of rs2228570 (c.2T>C) was detected by PCR-restriction fragment length polymorphism.

RESULTS

The frequencies of GG genotype and G allele of rs1544410 were significantly higher in patients with AA than in controls. Further analysis indicated that rs1544410 and rs7975232 polymorphisms were correlated with the risk to nonsevere AA, while rs2228570 was relevant to severe AA. Moreover, TT carriers of rs2228570 were closely associated with a poor response to treatment and a higher risk of myelodysplastic syndrome/acute leukemia transformation, while CT carriers more easily evolved to overt paroxysmal nocturnal hemoglobinuria.

CONCLUSIONS

VDR polymorphisms may contribute to susceptibility to AA and influence the severity and prognosis of AA in a Chinese population.

Evaluation of Fluorescently Labeled Aerolysin as a New Kind of Reagent for Flow Cytometry Tests: Optimization of Use of FLAER, Hints, and Limits

OBJECTIVES

Diagnostic tests for paroxysmal nocturnal hemoglobinuria (PNH) are currently based on flow cytometry techniques. Typically, these tests use antibodies against glycosylphosphatidylinositol (GPI)-anchored proteins, but a new approach has been described recently, using a novel reagent named FLAER (fluorescently labeled aerolysin). In this work, we evaluate the performance and highlight the peculiarities of using this new reagent.

RESULTS

We investigated the general conditions of staining and explored optimal labeling settings. We found that the kinetics of the FLAER labeling is slightly different from that of antibodies. Our results led us to select a 30-minute incubation period at room temperature using 50 nmol/L as a final concentration of FLAER. As the nonspecific binding was dependent on the balance between FLAER and its ligand, the number of target cells was also found critical. In addition, sample preparation affected FLAER staining, and the lyse-before-stain preparation was preferred. Interestingly, FLAER affinity seems restricted to certain types of GPI anchors, making it unsuitable for exploration of RBCs. Finally, we aimed to evaluate FLAER as a possible single diagnostic tool; we studied cellular background in non-PNH samples and found a limit of detection close to 0.01% in optimal conditions.

CONCLUSIONS

The performance of the FLAER labeling on leukocytes proves that this reagent is a valuable tool for PNH diagnosis and particularly appropriate for high-sensitivity tests in laboratories aiming to detect minor PNH clones.

Evaluation of paroxysmal nocturnal hemoglobinuria screening by flow cytometry through multicentric interlaboratory comparison in four countries

OBJECTIVES

Paroxysmal nocturnal hemoglobinuria (PNH) is currently diagnosed by flow cytometry; although highly sensitive, its interpretation and reporting appear as critical as its technique. Thus, we developed a quality control scheme for the French-speaking region based on the international recommendations for PNH screening.

METHODS

After a topical workshop, we proposed a 1-year, two-step survey program to any volunteering French-speaking clinical laboratory. The first survey consisted of sending raw data files to evaluate gating and the interpretation strategy of each center. The second stipulated sending fresh whole-blood samples to evaluate the whole process and its practice.

RESULTS

Forty-nine participants from voluntary centers returned results for each of the two successive surveys. On virtual survey, 27% reported false-positive PNH created by immature granulocytes, whereas the minor PNH clone was not detected by 9%. On fresh survey, 63% of centers used at least the same six-color combination (CD24, CD14, CD33, CD15, CD45, and fluorescent aerolysin), and nearly 70% of participants were able to perform a sensitivity test less than 0.1% on neutrophils. All participants detected the major PNH clone, yet 16% returned false-positive results for the non-PNH clone case.

CONCLUSIONS

We succeeded in rallying numerous French-speaking clinical laboratories for both surveys and in harmonizing the technical practice by highlighting common pitfalls.

Flow cytometry screening for paroxysmal nocturnal hemoglobinuria: A single-center experience in Saudi Arabia

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired clonal hematopoietic stem cell disorder, characterized by the deficiency of glycosylphosphatidylinositol (GPI) that anchors proteins in cell membranes. PNH is manifest variously with hemoglobinuria, thrombosis, or bone marrow failure. This retrospective study was aimed at assessing the incidence and characteristics of patients diagnosed with PNH in the King Fisal Specialist Hospital and research center.

METHODS

Patients referred for PNH diagnosis at King Faisal Specialist Hospital and Research Centre, Riyadh, during the 2-year period (2012-2013) were included in the analysis. Peripheral blood samples were used for multi-parametric flow cytometry analysis based on fluorescent inactive aerolysin (FLAER), and the markers, CD235a and CD59 on red blood cells (RBCs), and CD14, CD45, CD64, CD24, and CD15 on white blood cells (WBCs) exclusively monocytes and granulocytes. Univariate analysis of the disease characteristics was performed.

RESULTS

Of the 366 samples submitted for PNH screening, 14 were positive (4%) and 11 were evaluable. Of the 11 patients analyzed, 8 patients (73%) presented with aplastic anemia, 1 patient (9%) each with pancytopenia, Budd-Chiari syndrome, and immune thrombocytopenia purpura. All samples showed type II and III GPI-deficient clones with a median clone size of 15% (range, 0.7%-56%) in the RBCs, and 63% (range, 3.8%-100%) in WBCs (monocytes and granulocytes).

CONCLUSIONS

This study confirms the rarity of PNH and its predominant presentation as aplastic anemia or thrombosis in a Saudi Arabian population, similar to the worldwide incidence.

[Paroxysmal nocturnal hemoglobinuria: An unknown cause of thrombosis?]

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired disorder of hematopoietic stem cells. Somatic mutation in the phosphatidylinositol glycan class A (PIG-A), X-linked gene, is responsible for a deficiency in glycosphosphatidylinositol-anchored proteins (GPI-AP). The lack of one of the GPI-AP complement regulatory proteins (CD55, CD59) leads to hemolysis. The disease is diagnosed with hemolytic anemia, marrow failure and thrombosis. Thromboembolic complication occurs in 30% of patient after 10 years of follow-up and is the first event in one out of 10 patients. The two most common sites are hepatic and cerebral veins. These locations are correlated with high risk of death. Currently, these data are balanced with the use of a monoclonal antibody (Eculizumab), which has significantly improved the prognosis with a survival similar to general population after 36 months of follow-up. Anticoagulant treatment is recommended after a thromboembolic event but has no place in primary prophylaxis.

Screening of patients with idiopathic venous thromboembolism for paroxysmal nocturnal hemoglobinuria clones

Paroxysmal nocturnal hemoglobinuria (PNH) is an uncommon disorder characterized by hemolysis, thrombosis and marrow failure. Whereas venous and arterial thrombosis is a very common symptom of the disease, the frequency of PNH clones in patients with unexplained venous thromboembolism, including deep vein thrombosis and pulmonary embolism, has not been studied. We conducted a cross sectional study evaluating the presence of PNH clones in patients with prevalent venous thromboembolism using a high sensitivity flow cytometry assay for erythrocytes and neutrophils. Among the 388 patients enrolled in the study one patient had a detectable PNH clone of 0.02% in the neutrophil population (0.26%; 95% CI 0.05 to 1.45) and no detectable erythrocyte clone. We conclude that the presence of PNH clones in patients with idiopathic venous thrombosis is rare. Screening for PNH clones among VTE patients might be better reserved for patients with signs of hemolysis.

Pathophysiology, diagnosis, and treatment of paroxysmal nocturnal hemoglobinuria: a review

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired disorder of the hematopoietic stem cell that makes blood cells more sensitive to the action of complement. Patients experience intravascular hemolysis, smooth muscle dystonia, renal failure, arterial and pulmonary hypertension, recurrent infectious diseases and an increased risk of notably dreadful thrombotic complications. The diagnosis is made by flow cytometry. Efforts have been recently performed to improve the sensitivity and the standardization of this technique. PNH is frequently associated with aplastic anemia or low-risk myelodysplasia and may be asymptomatic. Management of the classical form of PNH has been dramatically revolutionized by the development of eculizumab, which brings benefits in terms of hemolysis, quality of life, renal function, thrombotic risk, and life expectancy. Prophylaxis and treatment of arterial and venous thrombosis currently remain a challenge in PNH.

Standardizing leucocyte PNH clone detection: an international study

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Immunophenotyping of paucicellular samples

Immunophenotyping of paucicellular samples may represent a diagnostic challenge in the flow cytometry (FC) laboratory routine, as the scarcity of cells limits the number of tests that can be performed. Specimens such as fine needle aspirates (FNA), human body fluids (BF), cerebrospinal fluid (CSF), or ocular fluid (OF) sent for FC investigations in the case of suspicion of lymphoma, or for lymphoma monitoring, may contain very low numbers of cells. In these cases, it is mandatory to obtain the largest amount possible of useful information from a single tube. The basic protocol described in this unit provides a method that combines the use of multiple monoclonal antibodies (MAbs) with a Boolean gating strategy to identify and quantify the main lymphocyte populations, as well as to detect lymphomatous B cells or any aberrant T cell expression, if present, in paucicellular samples.

An inter-laboratory comparison of PNH clone detection by high-sensitivity flow cytometry in a Russian cohort

OBJECTIVES

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal stem cell disorder characterized by partial or absolute deficiency of glycophosphatidyl-inositol (GPI) anchor-linked surface proteins on blood cells. A lack of precise diagnostic standards for flow cytometry has hampered useful comparisons of data between laboratories. We report data from the first study evaluating the reproducibility of high-sensitivity flow cytometry for PNH in Russia.

METHODS

PNH clone sizes were determined at diagnosis in PNH patients at a central laboratory and compared with follow-up measurements in six laboratories across the country. Analyses in each laboratory were performed according to recommendations from the International Clinical Cytometry Society (ICCS) and the more recent 'practical guidelines'. Follow-up measurements were compared with each other and with the values determined at diagnosis.

RESULTS

PNH clone size measurements were determined in seven diagnosed PNH patients (five females, two males: mean age 37 years); five had a history of aplastic anemia and three (one with and two without aplastic anemia) had severe hemolytic PNH and elevated plasma lactate dehydrogenase. PNH clone sizes at diagnosis were low in patients with less severe clinical symptoms (0.41-9.7% of granulocytes) and high in patients with severe symptoms (58-99%). There were only minimal differences in the follow-up clone size measurement for each patient between the six laboratories, particularly in those with high values at diagnosis.

CONCLUSIONS

The ICCS-recommended high-sensitivity flow cytometry protocol was effective for detecting major and minor PNH clones in Russian PNH patients, and showed high reproducibility between laboratories.

Laboratory tests for paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematological disorder that is often suspected in a patient presenting with non-immune hemolytic anemia associated with pancytopenia or venous thrombosis. This disorder is a consequence of acquired somatic mutations in the phosphatidylinositol glycan class A (PIG-A) gene in the hematopoietic stem cells (HSC) of patients. The presence of these mutations leads to production of blood cells with decreased glycosyl phosphatidylinositol-anchored cell surface proteins, making red blood cells derived from the clone more sensitive to complement mediated hemolysis. The diagnosis of PNH may be difficult in some cases due a low proportion of PNH cells in the blood and occasionally due to difficulties in selecting the most appropriate diagnostic studies. The latest generation of tests allow for detection of very small populations of PNH cells, for following the natural course and response to therapy of the disease, and for helping to decide when to initiate therapy with monoclonal antibody targeting the terminal complement protein C5 (Eculizumab), anticoagulation, and in some cases allogeneic HSC transplant. In this article, we review the different diagnostic tests available to clinicians for PNH diagnosis.

Flow cytometry for hematopoietic cells

Within the last 25 years, flow cytometry and fluorescence-activated cell sorting have emerged as both routine diagnostic tools in clinical medicine and as advanced analytic tools critical in performing scientific research. This chapter aims at summarizing the use of flow cytometry in benign and malignant hematology and the monitoring of inherited and acquired immunodeficiency states. Numerous figures are provided from our laboratories at Massachusetts General Hospital that illustrate examples of these conditions. The chapter also describes novel flow cytometry-based imaging techniques, the combination of flow cytometry and mass spectrography, new software tools, and some future directions and applications of advanced instrumentation for flow cytometry.

Platelets and erythrocyte-bound platelets bind infectious HIV-1 in plasma of chronically infected patients

Chronic HIV-1 infection is associated with persistent viremia in most patients, but it remains unclear how free virus may survive the potential hostile effects of plasma. We investigated whether sites might exist on the surfaces of circulating blood cells for protection of infectious HIV-1 particles. Red blood cells (RBC) either from blood of uninfected normal individuals, or from blood obtained without EDTA from chronically infected HIV-1 patients, invariably contained a small number of RBC having attached platelets as determined by flow cytometry, light microscopy, and immunofluorescence microscopy. After mixing normal RBC with platelet-rich plasma, discrete populations of RBC, platelets, and complexes of platelets attached to RBC were purified by fluorescence-activated cell sorting. Upon incubation of purified cells or platelets with HIV-1 followed by washing and co-incubation with CD4-positive peripheral blood mononuclear cells (PBMC), platelets, and platelet-RBC complexes, but not platelet-free RBC, caused infection of PBMC. Infection was prevented by pre-treating the platelet-RBC complexes with EDTA. Plasma and RBC (comprising a RBC/platelet-RBC mixture) from chronically infected patients with low viral loads were also co-incubated with PBMC ex vivo to determine the presence of infectious HIV-1. All freshly isolated plasmas from the HIV-1-infected donors, obtained in the absence of anticoagulant, were noninfectious. Interestingly, the RBC from most of the patients caused cell-cell infection of PBMC that was prevented by stripping the RBC with EDTA. A monoclonal antibody to DC-SIGN partially inhibited cell-cell HIV-1 infection of PBMC by normal RBC pre-incubated with platelets and HIV-1. We conclude: (a) platelet-free EDTA-free plasma from chronically infected HIV-1 patients, although containing viral RNA, is an environment that lacks detectable infectious HIV-1; (b) platelets and platelet-RBC complexes, but not purified RBC, bind infectious HIV-1; (c) DC-SIGN, and possibly other C-type lectins, may represent binding sites for infectious HIV-1 on platelets and platelet-RBC complexes.

A prospective multicenter study of paroxysmal nocturnal hemoglobinuria cells in patients with bone marrow failure

Background

Paroxysmal nocturnal hemoglobinuria (PNH), a rare clonal hematopoietic stem cell disorder, is characterized by chronic, uncontrolled complement activation leading to intravascular hemolysis and an inflammatory prothrombotic state. The EXPLORE study aimed to determine the prevalence of undiagnosed PNH in patients with aplastic anemia (AA), myelodysplastic syndrome (MDS), and/or other bone marrow failure (BMF) syndromes and the effect of PNH clone size on hemolysis.

Methods

Patients, selected from medical office chart reviews, had blood samples collected for hematologic panel testing and for flow cytometry detection of PNH clones.

Results

Granulocyte PNH clones ≥ 1% were detected in 199 of all 5,398 patients (3.7%), 93 of 503 AA patients (18.5%), 50 of 4,401 MDS patients (1.1%), and 3 of 130 other BMF patients (2.3%). Higher-sensitivity analyses detected PNH clones ≥ 0.01% in 167 of 1,746 patients from all groups (9.6%) and in 22 of 1,225 MDS patients (1.8%), 116 of 294 AA patients (39.5%), and four of 54 other BMF patients (7.8%). Among patients with PNH clones ≥ 1%, median clone size was smaller in patients with AA (5.1%) than in those with MDS (17.6%) or other BMF (24.4%), and the percentage of patients with lactate dehydrogenase levels (a marker for intravascular hemolysis) ≥ 1.5 × upper limit of normal was smaller in patients with AA (18.3%) than in those with MDS (42.0%).

Conclusions

These results confirm the presence of PNH clones in high-risk patient groups and suggest that screening of such patients may facilitate patient management and care.

A systematic analysis of bone marrow cells by flow cytometry defines a specific phenotypic profile beyond GPI deficiency in paroxysmal nocturnal hemoglobinuria

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is a unique disorder caused by a PIG-A gene mutation in a stem cell clone. Its clinical picture can sometimes make challenging the distinction from other disorders, and especially from myelodysplastic syndromes (MDS), since both diseases correlate with cytopenias and morphological abnormalities of bone marrow (BM) cells. Recently, flow cytometry (FC) has been proposed to integrate the morphologic assessment of BM dysplasia, and thus to improve the diagnostics of MDS.

METHODS

In the present study, we have analyzed systematically FC data resulting from the study of BM cells from patients with PNH and MDS.

RESULTS

Our data demonstrated abnormalities in PNH beyond the deficiency of glycosylphosphatidylinositol-linked proteins and the application of a systematic approach allowed us to separate effectively MDS and PNH in a cluster analysis and to highlight disease-specific abnormalities. Indeed, the parallel evaluation of some key parameters, i.e. patterns of expression of CD45 and CD10, provided information with practical diagnostic usefulness in the distinction between PNH and MDS. Moreover, the hypo-expression of CD36 that we observed on monocytes might be related to the thrombotic tendency in PNH.

CONCLUSIONS

We investigated systematically the phenotypic profile of BM cells from patients with PNH; our data provide useful antigenic patterns to solve between PNH and MDS, sometimes morphologically overlapping. Moreover, some PNH-related phenotypic changes might be involved in the physiopathology of the disease and further studies addressing this issue are warranted.

Flow cytometric testing for paroxysmal nocturnal hemoglobinuria: CD64 is better for gating monocytes than CD33

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is diagnosed by documenting partial or complete absence of glycosyl phosphatidyl inositol (GPI)-associated ligands in neutrophils, monocytes, and red blood cells (RBCs). The monocytes can be separated by their bright expression of either CD33 or CD64. This paper compares the utility of CD33- vs CD64-based monocyte gating in flow cytometric testing for PNH.

METHODS

One hundred and nineteen cases tested for PNH by flow cytometry were included in the study. Both the total number of monocytes and the number of GPI-deficient monocytes gated with CD33 or CD64 were compared. The clustering pattern and any other unusual patterns were noted and investigated.

RESULTS

CD64 staining showed more distinct separation of the monocyte cluster than did CD33 staining. The difference between the number of monocytes gated by CD33 and CD64 staining ranged from -26 to +32% (median 1.60%, average 1.69%). Six patients had GPI-deficient monocytes by both CD33- and CD64-based gating, ranging from 0.02 to 83.23%. There were no patients who showed GPI-deficient monocytes by one but not the other gating. The presence of blasts in patients with acute leukemia resulted in abnormal cluster patterns, both by CD33- and CD64-based gating.

CONCLUSIONS

CD64-based gating showed more distinct clustering of monocytes than CD33-based gating, allowing for objective separation. The number of monocytes in total and GPI-deficient monocytes derived from both gating strategies was comparable.