PIG-A mutations in normal hematopoiesis

Comparison of human leukocyte antigen in patients with paroxysmal nocturnal hemoglobinuria of different clone sizes

Glycosylphosphatidylinositol-anchored protein-deficient hematopoietic stem and progenitor cell development caused by PIGA mutations cannot fully explain the pathogenesis of paroxysmal nocturnal hemoglobinuria (PNH). Herein, patients newly diagnosed with PNH at our hospital between April 2019 and April 2021 were recruited. The human leukocyte antigen (HLA) class I and II loci were analyzed, and patients were stratified by PNH clone sizes: small (< 50%) and large (≥ 50%). In 40 patients (29 males; 72.5%), the median PNH clone size was 72%. Thirteen (32.5%) and twenty-seven (67.5%) patients harbored small and large PNH clones, respectively. DRB1*15:01 and DQB1*06:02 had higher frequencies in patients with PNH than in healthy controls (adjusted P-value = 4.10 × 10-4 and 4.10 × 10-4, respectively). Whole HLA class I and II allele contributions differed (P = 0.046 and 0.065, not significant difference) when comparing patients with small and large PNH clones. B*13:01 and C*04:01 allelic frequencies were significantly higher in patients with small clones (P = 0.032 and P = 0.032, respectively). Patients with small clones had higher class II HLA evolutionary divergence (HED) (P = 0.041) and global class I and II HED (P = 0.019). In the entire cohort, 17 HLA aberrations were found in 11 (27.5%) patients. No significant differences in HLA aberrations were found between patients with small or large clones. In conclusion, patients with small clones tended to have a higher frequency of immune attack-associated alleles. A higher HED in patients with small clones may reflect a propensity for T cell-mediated autoimmunity. HLA aberrations were similar between patients with small and large clones.

Diagnostic evaluation in bone marrow failure disorders: what have we learnt to help inform the transplant decision in 2024 and beyond?

Aplastic anemia (AA) is the prototypical bone marrow failure syndrome. In the current era of readily available 'molecular annotation', application of comprehensive next-generation sequencing panels has generated novel insights into underlying pathogenetic mechanisms, potentially leading to improvements in personalized therapeutic approaches. New evidence has emerged as to the role of somatic loss of HLA class I allele expression in 'immune-mediated' AA, associated molecular aberrations, and risk of clonal evolution. A deeper understanding has emerged regarding the role of 'myeloid' gene mutations in this context, translating patho-mechanistic insights derived from wider clinical and translational research within the myeloid disorder arena. Here, we review contemporary 'tools' which aid in confirmation of a diagnosis of AA, with an additional focus on their potential in guiding therapeutic options. A specific emphasis is placed upon interpretation and integration of this detailed diagnostic information and how this may inform optimal transplantation strategies.

The immunologic abnormalities in patients with paroxysmal nocturnal hemoglobinuria are associated with disease progression

OBJECTIVES

To suggest the presence of a hyperimmune state in patients, and indicate that immune system attack on glycosylphosphatidylinositol (+) (GPI+) cells while escaping GPI- cell immunity.

METHODS

We retrospective the immune cell subtypes in peripheral blood from 25 patients visiting Tianjin Medical University General Hospital, Tianjin, China, with classical paroxysmal nocturnal hemoglobinuria (PNH) and 50 healthy controls.

RESULTS

The total CD3+ and CD3+CD8+ cell levels were higher in patients with PNH. The CD3+ cells are positively, correlated with lactate dehydrogenase (LDH; r=0.5453, p=0.0040), indirect bilirubin (r=0.4260, p=0.0379) and Flear- cells in monocytes (r=0.4099, p=0.0303). However, a negative correlation was observed between CD3+ cells and hemoglobin (r= -0.4530, p=0.0105). The total CD19+ cells decreased in patients, and CD19+ cells were negatively correlated with LDH (r= -0.5640, p=0.0077) and Flear- cells in monocytes (r= -0.4432, p=0.0341). Patients showed an increased proportion of total dendritic cells (DCs), with a higher proportion of myeloid DCs (mDCs) within the DC population. Moreover, the proportion of mDC/DC was positively correlated with CD59- cells (II + III types) in red cells (r=0.7941, p=0.0004), Flear- cells in granulocytes (r=0.5357, p=0.0396), and monocytes (r=0.6445, p=0.0095).

CONCLUSION

Our results demonstrated that immune abnormalities are associated with PNH development.

Case report: Immune pressure on hematopoietic stem cells can drastically expand glycosylphosphatidylinositol-deficient clones in paroxysmal nocturnal hemoglobinuria

Introduction

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematological disease characterized by intravascular hemolysis, thrombosis, and bone marrow (BM) failure. Although PNH is caused by excessive proliferation of hematopoietic stem cell (HSC) clones with loss of function mutations in phosphatidylinositol N-acetylglucosaminyltransferase subunit A (PIGA) genes, what drives PNH clones to expand remains elusive.

Case description

We present a case of a 26-year-old female who presented with hemolytic anemia, thrombocytopenia, and leukopenia. Flow cytometry analysis of peripheral blood showed that 71.9% and 15.3% of the granulocytes and erythrocytes were glycosylphosphatidylinositol-anchored protein deficient (GPI[-]) cells. The patient was diagnosed with PNH with non-severe aplastic anemia. Deep-targeted sequencing covering 390 different genes of sorted GPI(-) granulocytes revealed three different PIGA mutations (p.I69fs, variant allele frequency (VAF) 24.2%; p.T192P, VAF 5.8%; p.V300fs, VAF 5.1%) and no other mutations. She received six cycles of eculizumab and oral cyclosporine. Although the patient's serum lactate dehydrogenase level decreased, she remained dependent on red blood cell transfusion. Six months after diagnosis, she received a syngeneic bone marrow transplant (BMT) from a genetically identical healthy twin, following an immune ablative conditioning regimen consisting of cyclophosphamide 200 mg/kg and rabbit anti-thymocyte globulin 10 mg/kg. After four years, the patient's blood count remained normal without any signs of hemolysis. However, the peripheral blood still contained 0.2% GPI (-) granulocytes, and the three PIGA mutations that had been detected before BMT persisted at similar proportions to those before transplantation (p.I69fs, VAF 36.1%; p.T192P, VAF 3.7%; p.V300fs, VAF 8.6%) in the small PNH clones that persisted after transplantation.

Conclusions

The PNH clones that had increased excessively before BMT decreased, but persisted at low percentages for more than four years after the immunoablative conditioning regimen followed by syngeneic BMT. These findings indicate that as opposed to conventional theory, immune pressure on HSCs, which caused BM failure before BMT, was sufficient for PIGA-mutated HSCs to clonally expand to develop PNH.

The PIG-A gene mutation assay in human biomonitoring and disease

The blood cell phosphatidylinositol glycan class A (PIG-A) gene mutation assay has been extensively researched in rodents for in vivo mutagenicity testing and is now being investigated in humans. The PIG-A gene is involved in glycosyl phosphatidylinositol (GPI)-anchor biosynthesis. A single mutation in this X-linked gene can lead to loss of membrane-bound GPI anchors, which can be enumerated via corresponding GPI-anchored proteins (e.g., CD55) using flow cytometry. The studies published to date by different research groups demonstrate a remarkable consistency in PIG-A mutant frequencies. Moreover, with the low background level of mutant erythrocytes in healthy subjects (2.9-5.56 × 10-6 mutants), induction of mutation post genotoxic exposure can be detected. Cigarette smoking, radiotherapy, and occupational exposures, including lead, have been shown to increase mutant levels. Future applications of this test include identifying new harmful agents and establishing new exposure limits. This mutational monitoring approach may also identify individuals at higher risk of cancer development. In addition, identifying protective agents that could mitigate these effects may reduce baseline somatic mutation levels and such behaviors can be encouraged. Further technological progress is required including establishing underlying mechanisms of GPI anchor loss, protocol standardization, and the development of cryopreservation methods to improve GPI-anchor stability over time. If successful, this assay has the potential be widely employed, for example, in rural and low-income countries. Here, we review the current literature on PIG-A mutation in humans and discuss the potential role of this assay in human biomonitoring and disease detection.

Paroxysmal Nocturnal Hemoglobinuria: Biology and Treatment

Paroxysmal nocturnal hemoglobinuria (PNH) is a nonmalignant clonal hematopoietic disorder characterized by the lack of glycosylphosphatidylinositol-anchored proteins (GPI-APs) as a consequence of somatic mutations in the phosphatidylinositol glycan anchor biosynthesis class A (PIGA) gene. Clinical manifestations of PNH are intravascular hemolysis, thrombophilia, and bone marrow failure. Treatment of PNH mainly relies on the use of complement-targeted therapy (C5 inhibitors), with the newest agents being explored against other factors involved in the complement cascade to alleviate unresolved intravascular hemolysis and extravascular hemolysis. This review summarizes the biology and current treatment strategies for PNH with the aim of reaching a general audience with an interest in hematologic disorders.

Long noncoding RNA FAM157C contributes to clonal proliferation in paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare clonal disease of hematopoietic stem cells (HSCs). Long noncoding RNAs (lncRNAs) perform a wide range of biological functions, including the regulation of gene expression, cell differentiation, and proliferation, but their role in PNH remains unclear.CD59^- and CD59⁺ granulocytes and monocytes from 35 PNH patients were sorted. High-throughput sequencing was analyzed in 5 PNH patients, and differentially expressed lncRNAs and mRNAs were identified. The mRNAs with fragments per kilobase of exon model per million mapped fragments (FPKM) > 10 in at least 3 patients were selected, and experiments were performed to identify their upstream regulatory lncRNAs. The expression of selected mRNAs and lncRNAs was verified by qRT‒PCR, and the correlation of these expression patterns with clinical data from other 30 PNH patients was analyzed. Then, the functions of the lncRNAs were studied in the PIGA-KO-THP-1 cell line.Transcription analysis revealed 742 upregulated and 1376 downregulated lncRNAs and 3276 upregulated and 213 downregulated mRNAs. After deep screening, 8 highly expressed mRNAs that were related to the NF-κB pathway were analyzed to determine coexpression patterns. LINC01002, FAM157C, CTD-2530H12.2, XLOC-064331 and XLOC-106677 were correlated with the 8 mRNAs. After measuring the expression of these molecules in 30 PNH patients by qRT‒PCR, lncRNA FAM157C was verified to be upregulated in the PNH clone, and its expression levels were positively correlated with the LDH levels and CD59^- granulated and monocyte cell ratios. After knockdown of the FAM157C gene in the PIGA-KO-THP-1 cell line, we found that the cells were arrested in the G0/G1 phase and S phase, the apoptosis rate increased, and the cell proliferation decreased.LncRNA FAM157C was proven to promote PNH clone proliferation, and this is the first study to explore the role of lncRNAs in PNH.

The spectrum of paroxysmal nocturnal hemoglobinuria clinical presentation in a Brazilian single referral center

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematological disorder caused by the expansion of a hematopoietic clone harboring a somatic genetic variant in the PIG-A gene translating into a wide spectrum of clinical and laboratory changes, from intravascular hemolysis, thrombosis, and bone marrow failure to subclinical presentation. In this study, we retrospectively analyzed 87 consecutive cases (39 women; median follow-up, 18 months; range, 0–151 months) in whom a PNH clone was detected by flow cytometry between 2006 and 2019 seen at a single Brazilian referral center. The median age at diagnosis was 29 years (range, 8 to 83 years); 29 patients (33%) were initially classified as PNH/bone marrow failure, 13 (15%) as classic PNH, and 45 (52%) as subclinical PNH. The median overall survival (OS) of the entire cohort was not reached during follow-up, without significant differences between groups. At diagnosis, the median PNH clone size was 2.8% (range, 0 to 65%) in erythrocytes and 5.4% (range, 0 to 80%) in neutrophils. Fourteen patients experienced clone expansion during follow-up; in other 14 patients the clone disappeared, and in 18 patients it remained stable throughout the follow-up. A subclinical PNH clone was detected in three telomeropathy patients at diagnosis, but it was persistent and confirmed by DNA sequencing in only one case. In conclusion, PNH presentation was variable, and most patients had subclinical disease or associated with marrow failure and did not require specific anticomplement therapy. Clone size was stable or even disappeared in most cases.

Insights Into the Emergence of Paroxysmal Nocturnal Hemoglobinuria

Paroxysmal Nocturnal Hemoglobinuria (PNH) is a disease as simple as it is complex. PNH patients develop somatic loss-of-function mutations in phosphatidylinositol N-acetylglucosaminyltransferase subunit A gene (PIGA), required for the biosynthesis of glycosylphosphatidylinositol (GPI) anchors. Ubiquitous in eukaryotes, GPI anchors are a group of conserved glycolipid molecules responsible for attaching nearly 150 distinct proteins to the surface of cell membranes. The loss of two GPI-anchored surface proteins, CD55 and CD59, from red blood cells causes unregulated complement activation and hemolysis in classical PNH disease. In PNH patients, PIGA-mutant, GPI (-) hematopoietic cells clonally expand to make up a large portion of patients’ blood production, yet mechanisms leading to clonal expansion of GPI (-) cells remain enigmatic. Historical models of PNH in mice and the more recent PNH model in rhesus macaques showed that GPI (-) cells reconstitute near-normal hematopoiesis but have no intrinsic growth advantage and do not clonally expand over time. Landmark studies identified several potential mechanisms which can promote PNH clonal expansion. However, to what extent these contribute to PNH cell selection in patients continues to be a matter of active debate. Recent advancements in disease models and immunologic technologies, together with the growing understanding of autoimmune marrow failure, offer new opportunities to evaluate the mechanisms of clonal expansion in PNH. Here, we critically review published data on PNH cell biology and clonal expansion and highlight limitations and opportunities to further our understanding of the emergence of PNH clones.

Persistent imbalance, anti-apoptotic, and anti-inflammatory signature of circulating C-C chemokines and cytokines in patients with paroxysmal nocturnal hemoglobinuria

OBJECTIVE

Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal non-malignant disease in which hematopoietic cell apoptosis may play an important pathophysiological role. Previous studies of the content of phosphatidylinositol (3,4,5)-trisphosphate (PI(3,4,5)P3) indicated the possibility of remote transmission of anti-apoptotic signals between pathological and normal hematopoietic progenitors.

METHODS

The study determined the plasma levels of beta chemokines and cytokines in N = 19 patients with PNH and 31 healthy controls. The research material was peripheral blood plasma (EDTA) stored at -80 °C until the test. Beta chemokine and cytokine concentrations were tested in duplicate with Bio-Plex Pro Human Cytokine Assay (Bio-Rad, Hercules, CA, USA) using a Luminex 200 flow cytometer and xPONENT software (Luminex Corporation, Austin, TX, USA). In peripheral blood CD34+ cells we tested the proportions of PI(3,4,5)P3+ and Annexin binding apoptotic phenotype using FC and phosflow.

RESULTS

Compared to the control group, the PNH group showed a significant increase in the plasma concentration of some beta chemokines and cytokines, including MIP-1alpha/CCL3, eotaxin/CCL11, MCP1/CCL2, IL4 and G-CSF. In the group of PNH patients, a significant decrease in the concentration of some cytokines was also observed: RANTES/CCL5, MIP-1beta/CCL4, PDGF-BB and IL9. At the same time, the plasma concentrations of the chemokine IP-10/CXCL10 and the cytokines IFN-gamma, TNF, IL6 and IL10 showed no significant deviations from the values for the control group. Anti-apoptotic phenotype and phosphatidylinositol (3,4,5)-trisphosphate content in PNH clone of CD34+ cells were associated with the level of CCL3 and negatively associated with CCL5, CCL4, PDGF-BB and IL9.

CONCLUSIONS

This data suggest the existence of apoptotic and PI(3,4,5)P3 imbalance in PNH CD34+ cells driven by anti-apoptotic cytokine biosignature in PNH. Plasma cytokines and intracellular enzymes that regulate the phosphoinositide pathways may become a therapeutic target in PNH.

When does a PNH clone have clinical significance?

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired blood disease caused by somatic mutations in the phosphatidylinositol glycan class A (PIGA) gene required to produce glycophosphatidyl inositol (GPI) anchors. Although PNH cells are readily identified by flow cytometry due to their deficiency of GPI-anchored proteins, the assessment of the clinical significance of a PNH clone is more nuanced. The interpretation of results requires an understanding of PNH pathogenesis and its relationship to immune-mediated bone marrow failure. Only about one-third of patients with PNH clones have classical PNH disease with overt hemolysis, its associated symptoms, and the highly prothrombotic state characteristic of PNH. Patients with classical PNH benefit the most from complement inhibitors. In contrast, two-thirds of PNH clones occur in patients whose clinical presentation is that of bone marrow failure with few, if any, PNH-related symptoms. The clinical presentations are closely associated with PNH clone size. Although exceptions occur, bone marrow failure patients usually have smaller, subclinical PNH clones. This review addresses the common scenarios that arise in evaluating the clinical significance of PNH clones and provides practical guidelines for approaching a patient with a positive PNH result.

Immunologic effects on the haematopoietic stem cell in marrow failure

Acquired bone marrow failure (BMF) syndromes comprise a diverse group of diseases with variable clinical manifestations but overlapping features of immune activation, resulting in haematopoietic stem and progenitor cells (HSPC) damage and destruction. This review focuses on clinical presentation, pathophysiology, and treatment of four BMF: acquired aplastic anaemia, large granular lymphocytic leukaemia, paroxysmal nocturnal haemoglobinuria, and hypoplastic myelodysplastic syndrome. Autoantigens are speculated to be the inciting event that result in immune activation in all of these diseases, but specific pathogenic antigens have not been identified. Oligoclonal cytotoxic T cell expansion and an active role of proinflammatory cytokines, primarily interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α), are two main contributors to HSPC growth inhibition and apoptosis in BMF. Emerging evidence also suggests involvement of the innate immune system.

Time and residual hematopoiesis are crucial for PNH clones escape in hepatitis-associated aplastic anemia

The presence of paroxysmal nocturnal hemoglobinuria (PNH) clones in aplastic anemia (AA) suggests immunopathogenesis, but when and how PNH clones emerge and proliferate are unclear. Hepatitis-associated aplastic anemia (HAAA) is a special variant of AA, contrarily to idiopathic AA, in HAAA the trigger for immune activation is clearer and represented by the hepatitis and thus serves as a good model for studying PNH clones. Ninety HAAA patients were enrolled, including 61 males and 29 females (median age 21 years). Four hundred three of idiopathic AA have been included as controls. The median time from hepatitis to cytopenia was 50 days (range 0-180 days) and from cytopenia to AA diagnosis was 26 days (range 2-370 days). PNH clones were detected in 8 HAAA patients (8.9%) at diagnosis and in 73 patients with idiopathic AA (IAA) (18.1%). PNH cells accounted for 4.2% (1.09-12.33%) of red cells and/or granulocytes and were more likely to be detected in patients with longer disease history and less severe disease. During follow-up, the cumulative incidence of PNH clones in HAAA increased to 18.9% (17/90). Nine HAAA patients newly developed PNH clones, including six immunosuppressive therapy (IST) nonresponders. The clone size was mostly stable during follow-up, and only 2 of 14 patients showed increased clone size without proof of hemolysis. In conclusion, PNH clones were infrequent in newly diagnosed HAAA, but their frequency increased to one that was similar to the IAA frequency during follow-up. These results suggest that the PNH clone selection/expansion process is dynamic and takes time to establish, confirming that retesting for PNH clones during follow-up is crucial.

Ultradeep Sequencing Analysis of Paroxysmal Nocturnal Hemoglobinuria Clones Detected by Flow Cytometry: PIG Mutation in Small PNH Clones

OBJECTIVES

We aimed to determine whether small paroxysmal nocturnal hemoglobinuria (PNH) clones detected by flow cytometry (FCM) harbor PIG gene mutations with quantitative correlation.

METHODS

We analyzed 89 specimens from 63 patients whose PNH clone size was ≥0.1% by FCM. We performed ultradeep sequencing for the PIGA, PIGM, PIGT, and PIGX genes in these specimens.

RESULTS

A strong positive correlation between PNH clone size by FCM and variant allele frequency (VAF) of PIG gene mutation was identified (RBCs: r = 0.77, P < .001; granulocytes: r = 0.68, P < .001). Granulocyte clone size of 2.5% or greater and RBCs 0.4% or greater by FCM always harbored PIG gene mutations. Meanwhile, in patients with clone sizes of less than 2.5% in granulocytes or less than 0.4% in RBCs, PIG gene mutations were present in only 15.9% and 12.2% of cases, respectively. In addition, there was not a statistically significant positive correlation between FCM clone size and VAF or the presence or absence of a PIG mutation.

CONCLUSIONS

Our results showed that in small PNH clones PIG gene mutations were present in only a small portion without significant correlation to VAF or the presence or absence of a PIG mutation.

Bone Marrow Failure Syndromes, Overlapping Diseases with a Common Cytokine Signature

Bone marrow failure (BMF) syndromes are a heterogenous group of non-malignant hematologic diseases characterized by single- or multi-lineage cytopenia(s) with either inherited or acquired pathogenesis. Aberrant T or B cells or innate immune responses are variously involved in the pathophysiology of BMF, and hematological improvement after standard immunosuppressive or anti-complement therapies is the main indirect evidence of the central role of the immune system in BMF development. As part of this immune derangement, pro-inflammatory cytokines play an important role in shaping the immune responses and in sustaining inflammation during marrow failure. In this review, we summarize current knowledge of cytokine signatures in BMF syndromes.

Evaluation of PIG-A-mutated granulocytes and ex-vivo binucleated micronucleated lymphocytes frequencies after breast cancer radiotherapy in humans

Although the PIG-A gene mutation frequency (MF) is considered a good proxy to evaluate the somatic MF in animals, evidence remains scarce in humans. In this study, a granulocyte PIG-A-mutant assay was evaluated in patients undergoing radiation therapy (RT) for breast cancer. Breast cancer patients undergoing adjuvant RT were prospectively enrolled. RT involved the whole breast, with (WBNRT) or without (WBRT) nodal area irradiation. Blood samples were obtained from participants before (T0) RT, and T1, T2, and T3 samples were collected 3 weeks after the initiation of RT, at the end of RT, and at least 10 weeks after RT discontinuation, respectively. The MF was assessed using a flow cytometry protocol identifying PIG-A-mutant granulocytes. Cytokinesis-blocked micronucleated lymphocyte (CBML) frequencies were also evaluated. Thirty patients were included, and five of them had received chemotherapy prior to RT. The mean (±SD) PIG-A MFs were 7.7 (±12.1) per million at T0, 5.2 (±8.6) at T1, 6.4 (±8.0) at T2 and 3.8 (±36.0) at T3. No statistically significant increases were observed between the PIG-A MF at T0 and the MFs at other times. RT significantly increased the CBML frequencies: 7.9 ‰ (±3.1‰) versus 33.6‰ (±17.2‰) (p < .0001). By multivariate analysis, the CBML frequency was correlated with age at RT initiation (p = .043) and irradiation volume at RT discontinuation (p = .0001) but not with chemotherapy. RT for breast cancer therapy failed to induce an increase in the PIG-A MF. The PIG-A assay in humans needs further evaluation, in various genotoxic exposures and including various circulating human cells.

Mutations in PIGA cause a CD52-/GPI-anchor-deficient phenotype complicating alemtuzumab treatment in T-cell prolymphocytic leukemia

OBJECTIVE

Infusional alemtuzumab followed by consolidating allogeneic hematopoietic stem cell transplantation in eligible patients is considered a standard of care in T-cell prolymphocytic leukemia (T-PLL). Antibody selection against CD52 has been associated with the development of CD52-negative leukemic T cells at time of relapse. Clinical implications and molecular mechanisms underlying this phenotypic switch are unknown.

METHODS

We performed flow cytometry and real-time-PCR for CD52-expression and next generation sequencing for PIGA mutational analyses.

RESULTS

We identified loss of CD52 expression after alemtuzumab treatment in two of 21 T-PLL patients resulting from loss of GPI-anchor expression caused by inactivating mutations of the PIGA gene. One patient with relapsed T-PLL exhibited a single PIGA mutation, causing a CD52-negative escape variant of the initial leukemic cell clone, preventing alemtuzumab-retreatment. The second patient with continued complete remission after alemtuzumab treatment harbored three different PIGA mutations that affected either the non-neoplastic T cell or the mononuclear cell compartment and resulted in symptomatic paroxysmal nocturnal hemoglobinuria. Next generation sequencing of T-PLL cells collected before the initiation of treatment revealed PIGA wild-type sequence reads in all 16 patients with samples available for testing.

CONCLUSION

These data indicate that PIGA mutations were acquired during or after completion of alemtuzumab treatment.

PIG-A gene mutation as a genotoxicity biomarker in human population studies: An investigation in lead-exposed workers

The rodent Pig-a gene mutation assay has demonstrated remarkable sensitivity in identifying in vivo mutagens, while much less is known about the value of the human PIG-A assay for risk assessment. To obtain more evidence of its potential as a predictive biomarker for carcinogen exposure, we investigated PIG-A mutant frequencies (MFs), along with performing the Comet assay and micronucleus (MN) test, in 267 workers occupationally exposed to lead. Multivariate Poisson regression showed that total red blood cell PIG-A MFs were significantly higher in lead-exposed workers (10.90 ± 10.7 × 10^-6 ) than in a general population that we studied previously (5.25 ± 3.6 × 10^-6 ) (p < .0001). In contrast, there was no increase in lymphocyte MN frequency or in DNA damage as measured by percentage comet tail intensity in whole blood cells. Current year worker blood lead levels (BLL), an exposure biomarker, were elevated (232.6 ± 104.6 μg/L, median: 225.4 μg/L); a cumulative blood lead index (CBLI) also was calculated based on a combination of current and historical worker BLL data. Chi-square testing indicated that PIG-A MFs were significantly related to CBLI (p = .0249), but independent of current year BLL (p = .4276). However, % comet tail intensity and MN frequencies were better associated with current year BLL than CBLI. This study indicates that the PIG-A assay could serve as biomarker to detect the genotoxic effects of lead exposure and demonstrates that a battery of genotoxicity biomarkers having mechanistic complementarity may be useful for comprehensively monitoring human carcinogenic risk.

Laboratory studies for paroxysmal nocturnal hemoglobinuria, with emphasis on flow cytometry

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired clonal hematopoietic stem cell disorder caused by somatic mutations in the PIG-A gene, leading to the production of blood cells with absent or decreased expression of glycosylphosphatidylinositol-anchored proteins, including CD55 and CD59. Clinically, PNH is classified into three variants: classic (hemolytic), in the setting of another specified bone marrow disorder (such as aplastic anemia or myelodysplastic syndrome) and subclinical (asymptomatic). PNH testing is recommended for patients with intravascular hemolysis, acquired bone marrow failure syndromes and thrombosis with unusual features. Despite the availability of consensus guidelines for PNH diagnosis and monitoring, there are still discrepancies on how PNH tests are carried out, and these technical variations may lead to an incorrect diagnosis. Herein, we provide a brief historical overview of PNH, focusing on the laboratory tests available and on the current recommendations for PNH diagnosis and monitoring based in flow cytometry.

FLAER Based Assay According to Newer Guidelines Increases Sensitivity of PNH Clone Detection

Flow cytometry has become 'gold standard' for detecting abnormal clones in paroxysmal nocturnal hemoglobinuria (PNH), aplastic anemia (AA) and myelodysplastic syndrome (MDS). This pilot study was conducted in 2015 with a primary aim to evaluate the utility of single tube fluorescent aerolysin (FLAER) based testing and its comparison with two tubes non-FLAER based testing (CD55, CD59, CD24 and CD66b) in detecting abnormal PNH clones in these newly diagnosed cases. The secondary aim was an attempt to distinguish PNH from AA/MDS cases associated with PNH clones based on clinical, laboratory features and clone size at diagnosis. In this study, the abnormal PNH clones were detected using a single tube FLAER based testing and two tubes non-FLAER based testing in all cases of PNH (n = 12), healthy subjects (n = 18) and AA/MDS with PNH clone (n = 9) and compared with clinical and laboratory features at diagnosis. The receiver operator curve (ROC) analysis defined the optimal cut-offs for FLAER in granulocytes (> 0.7%) and monocytes (> 0.9%). There was significant positive correlation between FLAER and non-FLAER based testing in these cells (r > 0.3 and p < 0.05). FLAER based testing helped us in picking up smaller clones which were missed by latter technique in four patients thereby increasing its sensitivity and also technically proved to be cost-effective (Rs. 1800 vs. Rs. 2100). Even in PNH patients, the clone size was slightly higher by using FLAER when compared to non-FLAER based antibodies panel. The clone size of monocytes was always higher than granulocytes in both PNH and AA/MDS groups. Bone marrow cellularity and mean size of granulocytes and monocytes clone at diagnosis showed a striking statistically significant 'p' value of < 0.0001 between these groups. In this pilot study, a single tube FLAER based PNH testing had improved clone detection in all cases of PNH, AA/MDS with PNH clones. The clone size was > 30% in majority of PNH cases whereas in AA/MDS, it was usually < 10% at diagnosis. Hence this newer technique not only increased the sensitivity of PNH clone detection but also proved to be cost-effective.

Study for the diagnostic screening of paroxsymal nocturnal hemoglobinuria in Turkey: Prospective multicentric evaluation of suspected patients

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disease presenting with variable and various clinical findings. PNH might be overlooked and diagnosis may be delayed due to low awareness about PNH. This is the first multicenter study in Turkey, investigating the efficiency of diagnostic screening of PNH by multiparameter flow cytometry (FCM) according to consensus guidelines.

METHODS

We evaluate the efficiency of consensus clinical indications for PNH testing with FCM in 1689peripheral blood samples from 20 centers between January 2014 and December 2017.

RESULTS

Overall, at the 20 centers contributing to this study, PNH clone were detected in 62/1689 samples (3.6%) by FCM test. 75.8% (n = 47) of patients with PNH clone had aplastic anemia, 3.2% (n = 2) had Coombs (-) hemolytic anemia, 6.5% (n = 4) had unexplained cytopenia, 3.2% (n = 2) had MDS with refractory anemia, 1.6% (n = 1) had hemoglobinuria and 9.7% (n = 6) had others (elevated LDH, splenomegaly, etc.). In contrast, we detect no PNH clone test in patients who were screened for unexplained thrombosis.

CONCLUSIONS

Our study showed that current clinical indications for PNH testing are highly efficient and diagnostic screening of suspected patients for PNH with FCM is recommended. However, advanced screening algorithms are required for patients presenting with unexplained thrombosis and normal complete blood count.

Ravulizumab: a novel C5 inhibitor for the treatment of paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare stem cell disorder characterized by hemolytic anemia, bone marrow failure, and thrombosis. Until recently, the complement inhibitor, eculizumab, was the only United States Food and Drug Administration (US FDA)-approved therapy for the treatment of PNH. Although effective, eculizumab requires a frequent dosing schedule that can be burdensome for some patients and increases the risk of breakthrough intravascular hemolysis. Ravulizumab, an eculizumab-like monoclonal antibody engineered to have a longer half-life, is intended to provide the same benefits as eculizumab but with a more convenient and effective dosing schedule. In two recently published phase III non-inferiority trials, ravulizumab was found to be non-inferior to eculizumab both in efficacy and safety for the treatment of patients with PNH. Based on these results, ravulizumab was approved by the US FDA on 21 December 2018 and is currently under regulatory review in both the European Union and Japan.

Molecular analysis of glycosylphosphatidylinositol anchor deficient aerolysin resistant isolates in gulf war i veterans exposed to depleted uranium

During the First Gulf War (1991) over 100 servicemen sustained depleted uranium (DU) exposure through wound contamination, inhalation, and shrapnel. The Department of Veterans Affairs has a surveillance program for these Veterans which has included genotoxicity assays. The frequencies of glycosylphosphatidylinositol anchor (GPIa) negative (aerolysin resistant) cells determined by cloning assays for these Veterans are reported in Albertini RJ et al. (2019: Environ Mol Mutagen). Molecular analyses of the GPIa biosynthesis class A (PIGA) gene was performed on 862 aerolysin-resistant T-lymphocyte recovered isolates. The frequencies of different types of PIGA mutations were compared between high and low DU exposure groups. Additional molecular studies were performed on mutants that produced no PIGA mRNA or with deletions of all or part of the PIGA gene to determine deletion size and breakpoint sequence. One mutant appeared to be the result of a chromothriptic event. A significant percentage (>30%) of the aerolysin resistant isolates, which varied by sample year and Veteran, had wild-type PIGA cDNA (no mutation). As described in Albertini RJ et al. (2019: Environ Mol Mutagen), TCR gene rearrangement analysis of these isolates indicated most arose from multiple T-cell progenitors (hence the inability to find a mutation). It is likely that these isolates were the result of failure of complete selection against nonmutant cells in the cloning assays. Real-time studies of GPIa resistant isolates with no PIGA mutation but with a single TCR gene rearrangement found one clone with a PIGV deletion and several others with decreased levels of GPIa pathway gene mRNAs implying mutation in other GPIa pathway genes. Environ. Mol. Mutagen. 60:470-493, 2019. © 2019 Wiley Periodicals, Inc.

Diagnosis and management of PNH: Review and recommendations from a Belgian expert panel

Despite its considerable morbidity and mortality, paroxysmal nocturnal haemoglobinuria (PNH) is still underdiagnosed. Patients with PNH can suffer from cardiovascular, gastrointestinal, neurological or haematological symptoms and refer to several specialists. The aim of this paper is to review the diagnosis and the management of PNH patients, with the primary focus on identifying high-risk groups. Additionally, the implementation and prognostic value of the defined high-risk groups will be commented on and the management of PNH patients is discussed from a Belgian perspective. Finally, based on the available data, recommendations are provided. Eculizumab is a potent C5 complement inhibitor and reduces intravascular haemolysis and thrombosis in PNH patients and improves their quality of life. As thrombosis is the main cause of death in PNH patients, identifying high-risk PNH patients in need of therapy is essential. Currently, novel complement inhibitors are in development and the first data seem promising. Another challenge in PNH is to identify new markers to assess the thrombotic risk to achieve a better risk-based prophylactic anti-thrombotic management. Finally, because of the low prevalence of the disease, PNH patients should be included in the prospective PNH registry, which will offer new insights on the natural course of the disease and the impact of treatment of PNH.

Spontaneous Remission in Paroxysmal Nocturnal Hemoglobinuria-Return to Health or Transition Into Malignancy?

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired syndrome characterized by intravascular hemolysis, thrombosis, and bone marrow failure. The disease is caused by a mutation in the PIG-A gene that leads to the lack of glycosylphosphatidylinositol-anchored complement regulatory molecules CD55 and CD59 on affected blood cell surfaces. In previous studies, spontaneous clinical remissions have been described. The disease manifestations are very heterogeneous, and we wanted to examine if true remissions and disappearance of the clone occur. In a follow-up of a nation-wide cohort of 106 Finnish patients with a PNH clone, we found six cases, where the clone disappeared or was clearly diminished. Two of the patients subsequently developed leukemia, while the other four are healthy and in clinical remission. According to our data, spontaneous remissions are not as frequent as described earlier. Since the disappearance of the PNH cell clone may indicate either a favorable or a poor outcome—remission or malignancy—careful clinical monitoring in PNH is mandatory. Nevertheless, true remissions occur, and further studies are needed to understand the immunological background of this phenomenon and to obtain a better understanding of the natural history of the disease.

Establishment of a flow cytometry assay for detecting paroxysmal nocturnal hemoglobinuria-type cells specific to patients with bone marrow failure

Minor populations of glycosylphosphatidylinositol-anchored protein-deficient (GPI[-]) cells in the peripheral blood may have a prognostic value in bone marrow failure (BMF). Our objective is to establish the optimal flow cytometry (FCM) assay that can discriminate GPI(-) populations specific to BMF from those of healthy individuals. To identify a cut-off that discriminates GPI(-) rare cells from GPI(+) cells, we determined a position of the borderline that separates the GPI(-) from GPI(+) cells on a scattergram by testing more than 30 healthy individuals, such that no GPI(-) dot fell into the upper left quadrant where fluorescein-labeled aerolysin (FLAER)^-CD11b⁺ granulocytes and CD55^-CD59^- glycophorin A⁺ erythrocytes were positioned. This method allowed us to define ≥ 0.003% CD11b⁺FLAER^- granulocytes and ≥ 0.005% glycophorin A⁺CD55^-CD59^- erythrocytes to be specific to BMF patients. Longitudinal cross-validation studies showed minimal (< 0.02%) inter-laboratory differences in the GPI(-) cell percentage. An analysis of 1210 patients with BMF revealed a GPI(-) cell population in 56.3% of patients with aplastic anemia and 18.5% of patients with myelodysplastic syndrome. The GPI(-) granulocyte percentages was 0.003-0.01% in 3.7% of patients. This FCM assay effectively identified an increase in the percentage of GPI(-) rare cells that are specific to BMF patients and allowed different laboratories to accurately detect 0.003-0.01% of pathological GPI(-) cells.

Diagnosis of Paroxysmal Nocturnal Hemoglobinuria: Recent Advances

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal hematopoietic stem cell disorder with its protean clinical manifestations. This is due to partial or complete absence of 'glycophosphatidyl-inositol-anchor proteins' (GPI-AP). The main aim of this review is to highlight various diagnostic modalities available, basic principle of each test and recent advances in the diagnosis of PNH. Recently among various tests available, the flow cytometry has become 'the gold standard' for PNH testing. In order to overcome the difficulties encountered by the testing and research laboratories throughout the world, International Clinical Cytometry Society has come up with guidelines regarding the indications for testing, protocol for sample collection, processing, panel of antibodies as well as gating strategies to be used, how to interpret the test and reporting format to be used. It is essential to test at least two GPI-linked markers on at least two different lineages particularly on red cells and granulocytes/monocytes. The fluorescent aerolysin combined with other monoclonal antibodies in multicolour flow cytometry offered an improved assay not only for diagnosis but also for monitoring of PNH clones. It is equally important to diagnose this rare entity with high index of suspicion.

Paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is a clonal haematopoietic stem cell (HSC) disease that presents with haemolytic anaemia, thrombosis and smooth muscle dystonias, as well as bone marrow failure in some cases. PNH is caused by somatic mutations in PIGA (which encodes phosphatidylinositol N-acetylglucosaminyltransferase subunit A) in one or more HSC clones. The gene product of PIGA is required for the biosynthesis of glycosylphosphatidylinositol (GPI) anchors; thus, PIGA mutations lead to a deficiency of GPI-anchored proteins, such as complement decay-accelerating factor (also known as CD55) and CD59 glycoprotein (CD59), which are both complement inhibitors. Clinical manifestations of PNH occur when a HSC clone carrying somatic PIGA mutations acquires a growth advantage and differentiates, generating mature blood cells that are deficient of GPI-anchored proteins. The loss of CD55 and CD59 renders PNH erythrocytes susceptible to intravascular haemolysis, which can lead to thrombosis and to much of the morbidity and mortality of PNH. The accumulation of anaphylatoxins (such as C5a) from complement activation might also have a role. The natural history of PNH is highly variable, ranging from quiescent to life-threatening. Therapeutic strategies include terminal complement blockade and bone marrow transplantation. Eculizumab, a monoclonal antibody complement inhibitor, is highly effective and the only licensed therapy for PNH.

[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.

Retinal vein occlusion and paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disorder associated with increased risk for thrombosis and reduced life expectancy. Retinal vein occlusion (RVO) is a frequent cause of vision loss but its relationship with PNH has not been studied systematically. Patients followed up for RVO in our ophthalmology department were screened for the presence of a PNH clone in peripheral blood by means of flow cytometry. The presence of other well-documented risk factors for RVO was also analyzed. In a series of 110 patients (54 males, median age of 67) we found no evidence of PNH. Most patients (97/110) had cardiovascular risk factors and/or hyperhomocysteinemia (67/110). Inherited thrombophilias were rare (three confirmed cases). Therefore, PNH does not appear to play a role in the development of RVO. However, this finding does not necessarily apply to young patients and/or those with no conventional risk factors for RVO, due to the low number of patients in these subgroups in our population.

Development of an in vitro PIG-A gene mutation assay in human cells

Mutagens can be carcinogens, and traditionally, they have been identified in vitro using the Salmonella 'Ames' reverse mutation assay. However, prokaryotic DNA packaging, replication and repair systems are mechanistically very different to those in the humans we inevitably seek to protect. Therefore, for many years, mammalian cell line genotoxicity assays that can detect eukaryotic mutagens as well as clastogens and aneugens have been used. The apparent lack of specificity in these largely rodent systems, due partly to their mutant p53 status, has contributed to the use of animal studies to resolve data conflicts. Recently, silencing mutations at the PIG-A locus have been demonstrated to prevent glycophosphatidylinositol (GPI) anchor synthesis and consequentially result in loss of GPI-anchored proteins from the cell's extracellular surface. The successful exploitation of this mutant phenotype in animal studies has triggered interest in the development of an analogous in vitro PIG-A mutation screening assay. This article describes the development of a robust assay design using metabolically active human cells. The assay includes viability and cell membrane integrity assessment and conforms to the future ideas of the 21st-century toxicology testing.

A population study using the human erythrocyte PIG-A assay

Erythrocyte-based PIG-A assay is sensitive and reliable in detecting exposure to mutagenetic agents in animal studies, but there are few data from human populations. In this study, we employed a method for detecting CD59 phenotypic variants, resulting from mutation in the PIG-A gene, in human red blood cells (RBCs), and determined the CD59-deficient RBC (RBC^CD59- ) frequencies in 217 subjects from general population. The majority of subjects had a relatively low mutant frequencies (MFs) (average, 5.25 ± 3.6 × 10^-6 , median, 4.38 × 10^-6 , for all subjects), but with males having a significantly greater MFs (5.97 ± 4.0 × 10^-6 ) than females (4.19 ± 2.5 ×10^-6 ). There was no correlation between MFs and age. In addition, MFs showed no difference between smoker and nonsmoker, and also no association with smoke duration in male subjects. However, there was a significant correlation between cigarette-pack-years which indicated that the MF was only slightly elevated with the increase of cigarette-pack-years. Moreover, intraindividual variations were investigated in three volunteer subjects over 300 days, and the MFs were relatively stable and repeatable. Furthermore, a pilot study by using white blood cell (WBC) assay based on labeling with FLAER was performed in volunteer subjects. The MFs of FLAER-deficient WBC (WBC^FLAER- ) and RBC^CD59- were consistently elevated in two subjects. Our findings provide baseline data that will be helpful in designing further studies using the PIG-A assay to monitor the genotoxic effects of carcinogens in human populations. Environ. Mol. Mutagen. 57:589-604, 2016. © 2016 Wiley Periodicals, Inc.

[Clinical and laboratory characteristics in patients of myelodysplastic syndrome with PNH clones]

OBJECTIVE

To analyze the clinical, laboratory characteristics and PIG-A gene mutations in patients of myelodysplastic syndromes (MDS) with PNH clones.

METHODS

218 MDS patients diagnosed from August 2013 to August 2015 were analyzed. The PIG-A gene mutations were tested in 13 cases of MDS with PNH clones, 17 cases of AA-PNH and 14 cases of PNH selected contemporaneously by PCR and direct sequencing.

RESULTS

13 (5.96%) MDS patients were detected with PNH clones (13/218 cases). 9 patients were treated with cyclosporin A (CsA). Patients showed hematological improvement (HI). There were significant differences between MDS-PNH and PNH patients in terms of granulocyte clone size, red cell clone size and LDH levels [19.2% (1.0%-97.7%) vs 60.2% (3.1%-98.0%), P=0.007; 4.3% (0-67.2%) vs 27.9% (2.5%-83.6%), P=0.026; 246 (89-2014) U/L vs 1137 (195-2239) U/L, P=0.049], while the differences were not statistically significant in patients between MDS-PNH and AA-PNH patients [19.2% (1.0%-97.7%) vs 23.2% (1.5%-96.0%), P=0.843; 4.3% (0-67.2%) vs 14.4% (1.1%-62.8%), P=0.079; 246 (89-2014) U/L vs 406 (192-1148) U/L, P=0.107]. PIG-A gene mutations were detected in 7 MDS-PNH patients, of them, six were missense mutations, one were frameshift mutation and four cases with the same mutation of c.356G>A (R119Q). The PIG-A gene mutations were also detected in 9/11 AA-PNH patients and 11/14 PNH patients, both of them had the mutation of c.356G>A (R119Q). The PIG-A gene mutations of MDS-PNH, AA-PNH, PNH patients were all small mutations, the majority of those (59%) were missense mutation and mainly located in exon 2.

CONCLUSION

MDS patients with PNH clones had better response to CsA, smaller PNH clone size. The PIG-A gene mutations of MDS-PNH patients mainly located in exon 2, which could be a mutational hotspot of these patients.

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.

Both PIGA and PIGL mutations cause GPI-a deficient isolates in the Tk6 cell line

Molecular analysis of proaerolysin selected glycosylphosphatidylinositol anchor (GPI-a) deficient isolates in the TK6 cell line was performed. Initial studies found that the expected X-linked PIGA mutations were rare among the spontaneous isolates but did increase modestly after ethyl methane sulfate (EMS) treatment (but to only 50% of isolates). To determine the molecular bases of the remaining GPI-a deficient isolates, real-time analysis for all the 25 autosomal GPI-a pathway genes was performed on the isolates without PIGA mutations, determining that PIGL mRNA was absent for many. Further analysis determined these isolates had several different homozygous deletions of the 5' region of PIGL (17p12-p22) extending 5' (telomeric) through NCOR1 and some into the TTC19 gene (total deletion >250,000 bp). It was determined that the TK6 parent had a hemizygous deletion in 17p12-p22 (275,712 bp) extending from PIGL intron 2 into TTC19 intron 7. Second hit deletions in the other allele in the GPI-a deficient isolates led to the detected homozygous deletions. Several of the deletion breakpoints including the original first hit deletion were sequenced. As strong support for TK6 having a deletion, a number of the isolates without PIGA mutations nor homozygous PIGL deletions had point mutations in the PIGL gene. These studies show that the GPI-a mutation studies using TK6 cell line could be a valuable assay detecting point and deletion mutations in two genes simultaneously.

Paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare bone marrow failure disorder that manifests with hemolytic anemia, thrombosis, and peripheral blood cytopenias. The absence of two glycosylphosphatidylinositol (GPI)-anchored proteins, CD55 and CD59, leads to uncontrolled complement activation that accounts for hemolysis and other PNH manifestations. GPI anchor protein deficiency is almost always due to somatic mutations in phosphatidylinositol glycan class A (PIGA), a gene involved in the first step of GPI anchor biosynthesis; however, alternative mutations that cause PNH have recently been discovered. In addition, hypomorphic germ-line PIGA mutations that do not cause PNH have been shown to be responsible for a condition known as multiple congenital anomalies-hypotonia-seizures syndrome 2. Eculizumab, a first-in-class monoclonal antibody that inhibits terminal complement, is the treatment of choice for patients with severe manifestations of PNH. Bone marrow transplantation remains the only cure for PNH but should be reserved for patients with suboptimal response to eculizumab.

Paroxysmal nocturnal hemoglobinuria clones in children with acquired aplastic anemia: a multicentre study

A multicentre study evaluating the presence of glycosil phosphatidyl-inositol (GPI)-negative populations was performed in 85 children with acquired aplastic anemia (AA). A GPI-negative population was observed in 41% of patients at diagnosis, 48% during immune-suppressive therapy (IST), and 45% in patients off-therapy. No association was found between the presence of a GPI-negative population at diagnosis and the response to IST. In addition, the response rate to IST did not differ between the patients who were GPI-positive at diagnosis and later developed GPI-negative populations and the 11 patients who remained GPI-positive. Two patients with a GPI-negative population >10%, and laboratory signs of hemolysis without hemoglobinuria were considered affected by paroxysmal nocturnal hemoglobinuria (PNH) secondary to AA; no thrombotic event was reported. Excluding the 2 patients with a GPI-negative population greater than 10%, we did not observe a significant correlation between LDH levels and GPI-negative population size. In this study monitoring for laboratory signs of hemolysis was sufficient to diagnose PNH in AA patients. The presence of minor GPI-negative populations at diagnosis in our series did not influence the therapeutic response. As occasionally the appearance of a GPI-negative population was observed at cyclosporine (CSA) tapering or AA relapse, a possible role of GPI-negative population monitoring during IST modulation may need further investigation.

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.

The role of decay accelerating factor in environmentally induced and idiopathic systemic autoimmune disease

Decay accelerating factor (DAF) plays a complex role in the immune system through complement-dependent and -independent regulation of innate and adaptive immunity. Over the past five years there has been accumulating evidence for a significant role of DAF in negatively regulating adaptive T-cell responses and autoimmunity in both humans and experimental models. This review discusses the relationship between DAF and the complement system and highlights major advances in our understanding of the biology of DAF in human disease, particularly systemic lupus erythematosus. The role of DAF in regulation of idiopathic and environmentally induced systemic autoimmunity is discussed including studies showing that reduction or absence of DAF is associated with autoimmunity. In contrast, DAF-mediated T cell activation leads to cytokine expression consistent with T regulatory cells. This is supported by studies showing that interaction between DAF and its molecular partner, CD97, modifies expression of autoimmunity promoting cytokines. These observations are used to develop a hypothetical model to explain how DAF expression may impact T cell differentiation via interaction with CD97 leading to T regulatory cells, increased production of IL-10, and immune tolerance.

Paroxysmal nocturnal hemoglobinuria and the age of therapeutic complement inhibition

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disease of hematopoietic stem cells due to a mutation in the PIG-A gene leading to a deficiency of GPI-anchored proteins. Lack of two specific GPI-anchored proteins, CD55 and CD59, leads to uncontrolled complement activation that result in both intravascular and extravascular hemolysis. Free hemoglobin leads to nitric oxide depletion that mediates the pathophysiology of some of the common clinical signs of PNH. Clinical symptoms of PNH include evidence of hemolytic anemia, bone marrow failure, smooth muscle dystonias and thromboses. Treatment options for patients with PNH include bone marrow transplantation, a therapy associated with high morbidity and mortality, or treatment with the complement inhibitor eculizumab. Eculizumab is a first-in-class anti-complement drug that in PNH has been shown to block complement-mediated hemolysis, reduce transfusion dependency, reduce thromboembolic complications and improve the quality of life (QoL) of patients.

Diagnosis of paroxysmal nocturnal hemoglobinuria in peripheral blood and bone marrow with six-color flow cytometry

AIM

Identification of paroxysmal nocturnal hemoglobinuria (PNH) by detecting a glycophosphatidylinositol-anchored defect by flow cytometry is presently the standard method of choice for diagnosing PNH. However, the selection of suitable markers will be critical and significantly affect the determination and quantification of PNH clones in various cell lineages.

MATERIALS & METHODS

In this study, we investigated the performance of various immunophenotypic markers including CD59, GPHA (a clustered antigen, CD235a), CD33, CD15 and fluorescent aerolysin (FLAER) combined with CD16, CD24 and CD14 in a PNH panel using six-color flow cytometry.

RESULTS

The results strongly indicate that these markers can collectively and effectively identify and quantify PNH clones in erythrocyte, granulocyte and monocyte populations derived from peripheral blood and bone marrow (BM). A sensitivity threshold as low as 0.01% in identifying PNH clones in erythrocyte and granulocyte populations from peripheral blood is achieved by this panel in a series dilution assay. In addition, a direct side-by-side comparison between BM and peripheral blood from the same patients suggests that the FLAER PNH test is capable of identifying to PNH clones in BM specimens.

CONCLUSION

The data support the premise that a six-color flow cytometry PNH panel using the combination of CD59, CD235a, CD33, CD15, FLAER, CD16, CD24 and CD14 can enhance and improve the current methods used in diagnosis and management of PNH by specifically identifying PNH clones in the erythrocyte, granulocyte and monocyte population.

The rate of spontaneous mutations in human myeloid cells

The mutation rate (μ) is likely to be a key parameter in leukemogenesis, but historically, it has been difficult to measure in humans. The PIG-A gene has some advantages for the detection of spontaneous mutations because it is X-linked, and therefore only one mutation is required to disrupt its function. Furthermore, the PIG-A-null phenotype is readily detected by flow cytometry. Using PIG-A, we have now provided the first in vitro measurement of μ in myeloid cells, using cultures of CD34+ cells that are transduced with either the AML-ETO or the MLL-AF9 fusion genes and expanded with cytokines. For the AML-ETO cultures, the median μ value was ∼9.4×10(-7) (range ∼3.6-23×10(-7)) per cell division. In contrast, few spontaneous mutations were observed in the MLL-AF9 cultures. Knockdown of p53 or introduction of mutant NRAS or FLT3 alleles did not have much of an effect on μ. Based on these data, we provide a model to predict whether hypermutability must occur in the process of leukemogenesis.

Frequency of paroxysmal nocturnal hemoglobinuria in patients attended in Belém, Pará, Brazil

BACKGROUND

Paroxysmal nocturnal hemoglobinuria is a hematological disease with complex physiopathology. It is genetically characterized by a somatic mutation in the PIG-A gene (phosphatidylinositol glycan anchor biosynthesis, class A), in which the best known antigens are DAF (decay accelerating factor or CD55) and MIRL (membrane inhibitor of reactive lysis or CD59).

OBJECTIVE

To determine the frequency of paroxysmal nocturnal hemoglobinuria in patients attended at the HEMOPA foundation from November 2008 to July 2009.

METHOD

Thirty patients, with ages ranging from two to 79 years old and suspected of having paroxysmal nocturnal hemoglobinuria were examined. All patients were immunophenotyped by flow cytometry for the CD5, CD59, CD16 and CD45 antigens.

RESULTS

Paroxysmal nocturnal hemoglobinuria was identified in nine of the thirty patients investigated. Another 3 cases had inconclusive results with CD59-negative labeling only for neutrophils. The highest frequency of paroxysmal nocturnal hemoglobinuria patients (7/9) and inconclusive cases (2/3) were between 19 years old and 48 years old, with a median of 28 years.

CONCLUSION

These results show the importance of flow cytometry to identify cases in which patients are deficient in only one antigen (CD59).