Biochemical background of paroxysmal nocturnal hemoglobinuria

Aplastic anemia and paroxysmal nocturnal hemoglobinuria in children and adults in two centers of Northern Greece

Bone marrow failure (BMF) syndromes are a group of various hematological diseases with cytopenia as a main common characteristic. Given their rarity and continuous progress in the field, we aim to provide data considering the efficiency and safety of the therapeutic methods, focusing on the treatment of aplastic anemia(AA) and paroxysmal nocturnal hemoglobinuria (PNH). We enrolled consecutive patients diagnosed with BMF in two referral centers of Northern Greece from 2008 to 2020. We studied 43 patients with AA (37 adults and 6 children/adolescents) and 6 with classical PNH. Regarding classical PNH, 4 patients have received eculizumab treatment with 1/4 presenting extravascular hemolysis. Among 43 patients with aplastic anemia, PNH clones were detected in 11. Regarding patients that did not receive alloHCT (n=15), 14/15 were treated with ATG and cyclosporine as first line, with the addition of eltrombopag in patients treated after its approval (n=9). With a median follow-up of 16.7 (1.8-56.2) months from diagnosis, 12/14 (85.7%) are alive (4-year OS: 85.1%). AlloHCT was performed in 28 patients. Five patients developed TA-TMA which did not resolve in 3/5 (all with a pre-transplant PNH clone). With the follow-up among survivors reaching 86.3 (6.3-262.4) months, 10-year OS was 56.9%, independently associated with PNH clones after adjusting for age (p=0.024). In conclusion, our real-world experience confirms that novel treatments are changing the field of BMF syndromes. Nevertheless, there is still an unmet need to personalize algorithms in this field.

Development of an anti-human complement C6 monoclonal antibody that inhibits the assembly of membrane attack complexes

Membrane attack complexes (MACs; C5b-9) assembled after complement activation can directly injure self-tissues, leading to various diseases. Eculizumab, a monoclonal antibody (mAb) against complement component C5, is being used in the clinic to treat diseases in which MAC-mediated tissue damage is a primary cause. However, C5 is not a selective target for MAC assembly inhibition, and some patients respond incompletely or not at all to the eculizumab treatment. Therefore, C6, the next essential component in the terminal pathway of complement activation, may be an alternative target for the selective inhibition of MAC formation. Surprisingly, few reports describe a functional blockade of C6 using a specific mAb. Here, we report the development of an anti-human C6 mAb (clone 1C9) that recognizes C6 both in free circulation and within C5b6 complexes. This mAb blocked C7 binding to C5b6 complexes and consequently inhibited MAC formation and protected affected paroxysmal nocturnal hemoglobinuria patient red blood cells from MAC-mediated damage in vitro. In addition, this mAb cross-reacts with rhesus monkey but not mouse complement C6. Finally, 1C9 significantly reduced human complement-mediated intravascular hemolysis in vivo in a mouse model. These results suggest that the anti-C6 mAb holds promise as a new therapeutic agent that selectively targets MAC for many complement-mediated pathological conditions.

Bone Marrow as a Source of Cells for Paroxysmal Nocturnal Hemoglobinuria Detection

Objectives

To determine fluorescently labeled aerolysin (FLAER) binding and glycophosphatidylinositol–anchored protein expression in bone marrow (BM) cells of healthy volunteers and patients with paroxysmal nocturnal hemoglobinuria (PNH) detected in peripheral blood (PB); compare PNH clone size in BM and PB; and detect PNH in BM by commonly used antibodies.

Methods

Flow cytometry analysis of FLAER binding to leukocytes and expression of CD55/CD59 in erythrocytes. Analysis of CD16 in neutrophils and CD14 in monocytes in BM.

Results

FLAER binds to all normal BM leukocytes, and binding increases with cell maturation. In PNH, lymphocytic clones are consistently smaller than clones of other BM cells. PNH clones are detectable in mature BM leukocytes with high specificity and sensitivity using common antibodies.

Conclusions

PNH clone sizes measured in mature BM leukocytes and in PB are comparable, making BM suitable for PNH assessment. We further demonstrate that commonly used reagents (not FLAER or CD55/CD59) can reliably identify abnormalities of BM neutrophils and monocytes consistent with PNH cells.

In Vivo Rat T-Lymphocyte Pig-a Assay: Detection and Expansion of Cells Deficient in the GPI-Anchored CD48 Surface Marker for Analysis of Mutation in the Endogenous Pig-a Gene

The Pig-a assay is being developed as an in vivo gene mutation assay for regulatory safety assessments. The assay is based on detecting mutation in the endogenous Pig-a gene of treated rats by using flow cytometry to measure changes in cell surface markers of peripheral blood cells. Here we present a methodology for demonstrating that phenotypically mutant rat T-cells identified by flow cytometry contain mutations in the Pig-a gene, an important step for validating the assay. In our approach, the mutant phenotype T-cells are sorted into individual wells of 96-well plates and expanded into clones. Subsequent sequencing of genomic DNA from the expanded clones confirms that the Pig-a assay detects exactly what it claims to detect-cells with mutations in the endogenous Pig-a gene. In addition, determining the spectra of Pig-a mutations provides information for better understanding the mutational mechanism of compounds of interest. Our methodology of combining phenotypic antibody labeling, magnetic enrichment, sorting, and single-cell clonal expansion can be used in genotoxicity/mutagenicity studies and in other general immunotoxicology research requiring identification, isolation, and expansion of extremely rare subpopulations of T-cells.

Buried Hydrogen Bond Interactions Contribute to the High Potency of Complement Factor D Inhibitors

Aberrant activation of the complement system is associated with diseases, including paroxysmal nocturnal hemoglobinuria and age-related macular degeneration. Complement factor D is the rate-limiting enzyme for activating the alternative pathway in the complement system. Recent development led to a class of potent amide containing pyrrolidine derived factor D inhibitors. Here, we used biochemical enzymatic and biolayer interferometry assays to demonstrate that the amide group improves the inhibitor potency by more than 80-fold. Our crystal structures revealed buried hydrogen bond interactions are important. Molecular orbital analysis from quantum chemistry calculations dissects the chemical groups participating in these interactions. Free energy calculation supports the differential contributions of the amide group to the binding affinities of these inhibitors. Cell-based hemolysis assay confirmed these compounds inhibit factor D mediated complement activation via the alternative pathway. Our study highlights the important interactions contributing to the high potency of factor D inhibitors reported recently.

The presence of CD55- and/or CD59-deficient erythrocytic populations in patients with rheumatic diseases reflects an immune-mediated bone-marrow derived phenomenon

Background

Complement has the potential to provoke severe impairment to host tissues, as shown in autoimmune diseases where complement activation has been associated with diminished CD55 and/or CD59 expression on peripheral blood cell membranes. The aim of this study was to evaluate the presence of CD55- and/or CD59-deficient erythrocytic populations in patients with different rheumatic diseases and to investigate possible correlations with clinical or laboratory parameters.

Material/Methods

CD55 and CD59 expression was evaluated in erythrocytes of 113 patients with rheumatic diseases, 121 normal individuals, and 10 patients with paroxysmal nocturnal hemoglobinuria (PNH) using the Sephacryl gel microtyping system. Ham and sucrose tests were also performed.

Results

Interestingly, the majority of patients (104/113, 92%) demonstrated CD55- and/or CD59-deficient erythrocytes: 47 (41.6%) with concomitant deficiency of CD55 and CD59, 50 (44.2%) with isolated deficiency of CD55, and 6 (6.2%) with isolated deficiency of CD59. In normal individuals, only 2 (1%) had concomitant CD55/CD59 negativity and 3 (2%) had isolated CD55 or CD59 deficiency. All PNH patients exhibited simultaneous CD55/CD59 deficiency. Positive Ham and sucrose tests were found only in PNH patients. There was no association between the CD55- and/or CD59-deficient erythrocytes and hemocytopenias or undergoing treatment. However, CD55 expression significantly influenced hemoglobin values (F=6.092, p=0.015).

Conclusions

This study provides evidence supporting the presence of erythrocytes with CD55 and/or CD59 deficiency in patients with rheumatic diseases. Moreover, CD55 deficiency on red cells influences hemoglobin concentration. Further studies using molecular techniques will clarify the exact pathophysiological mechanisms of this deficiency.

The pathophysiology of paroxysmal nocturnal hemoglobinuria and treatment with eculizumab

Paroxysmal nocturnal hemoglobinuria is a rare disorder of hemopoietic stem cells. Affected individuals have a triad of clinical associations – intravascular hemolysis, an increased risk of thromboembolism, and bone marrow failure. Most of the symptoms experienced in this disease occur due to the absence of complement regulatory proteins on the surface of the red blood cells. Complement activation is thus not checked and causes destruction of these cells. Eculizumab is a monoclonal antibody treatment which specifically binds to the complement protein C5, preventing its cleavage, and so halts the complement cascade and prevents the formation of the terminal complement proteins. Eculizumab prevents intravascular hemolysis, stabilizes hemoglobin levels, reduces or stops the need for blood transfusions, and improves fatigue and patient quality of life as well as reducing pulmonary hypertension, decreasing the risk of thrombosis and protecting against worsening renal function. It is not a curative therapy but has a great benefit on those with this rare debilitating condition.

Glycans as Biomarkers: Status and Perspectives

Protein glycosylation is a ubiquitous and complex co- and post-translational modification leading to glycan formation, i.e. oligosaccharide chains covalently attached to peptide backbones. The significance of changes in glycosylation for the beginning, progress and outcome of different human diseases is widely recognized. Thus, glycans are considered as unique structures to diagnose, predict susceptibility to and monitor the progression of disease. In the »omics« era, the glycome, a glycan analogue of the proteome and genome, holds considerable promise as a source of new biomarkers. In the design of a strategy for biomarker discovery, new principles and platforms for the analysis of relatively small amounts of numerous glycoproteins are needed. Emerging glycomics technologies comprising different types of mass spectrometry and affinity-based arrays are next in line to deliver new analytical procedures in the field of biomarkers. Screening different types of glycomolecules, selection of differentially expressed components, their enrichment and purification or identification are the most challenging parts of experimental and clinical glycoproteomics. This requires large-scale technologies enabling high sensitivity, proper standardization and validation of the methods to be used. Further progress in the field of applied glycoscience requires an integrated systematic approach in order to explore properly all opportunities for disease diagnosis.

A closer look at paroxysmal nocturnal hemoglobinuria

Knowledge of the molecular mechanisms leading to the paroxysmal nocturnal hemoglobinuria (PNH) phenotypes has substantially increased in the past two decades. The associated intravascular hemolysis, hypercoagulablilty, and bone marrow failure result in a wide range of clinical sequlae. Although treatment has usually been symptomatic through several modalities and rarely curative through hematopoietic cell transplantation, recent development of the novel targeted therapeutic agent eculizumab has offered new promises for this highly morbid and fatal disease. This review summarizes current knowledge of the pathophysiology, diagnostic modalities, clinical implications, and treatment approaches of patients with PNH.

Recent developments in the understanding and management of paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) has been recognised as a discrete disease entity since 1882. Approximately a half of patients will eventually die as a result of having PNH. Many of the symptoms of PNH, including recurrent abdominal pain, dysphagia, severe lethargy and erectile dysfunction, result from intravascular haemolysis with absorption of nitric oxide by free haemoglobin from the plasma. These symptoms, as well as the occurrence of thrombosis and aplasia, significantly affect patients' quality of life; thrombosis is the leading cause of premature mortality. The syndrome of haemolytic-anaemia-associated pulmonary hypertension has been further identified in PNH patients. There is currently an air of excitement surrounding therapies for PNH as recent therapeutic developments, particularly the use of the complement inhibitor eculizumab, promise to radically alter the symptomatology and natural history of haemolytic PNH.

Protection of erythrocytes from human complement–mediated lysis by membrane-targeted recombinant soluble CD59: a new approach to PNH therapy

Paroxysmal nocturnal hemoglobinuria (PNH) results from the expansion of a hematopoietic clone that is deficient in glycosylphosphatidylinositol-anchored molecules. PNH is characterized by chronic hemolysis with acute exacerbations due to the uncontrolled activity of complement on PNH cells, which lack the inhibitor of homologous complement, CD59. Symptoms include severe fatigue, hemoglobinuria, esophageal spasm, erectile dysfunction, and thrombosis. We report the use of a novel synthetically modified recombinant human CD59, rhCD59-P, a soluble protein that attaches to cell membranes. In vitro treatment of PNH erythrocytes with rhCD59-P resulted in levels of CD59 equivalent to normal erythrocytes and effectively protected erythrocytes from complement-mediated hemolysis. The administration of rhCD59-P to CD1 mice resulted in levels of CD59 on erythrocytes, which protected them from complement-mediated lysis. Thus, rhCD59-P corrects the CD59 deficiency in vitro and can bind to erythrocytes in an in vivo murine model, protecting the cells from the activity of human complement, and represents a potential therapeutic strategy in PNH.

Normal patterns of expression of glycosylphosphatidylinositol-anchored proteins on different subsets of peripheral blood cells: A frame of reference for the diagnosis of paroxysmal nocturnal hemoglobinuria

BACKGROUND

Evaluation of the expression of glycosylphosphatidylinositol-anchored membrane proteins (GPI-AP) is currently used for the diagnosis of paroxysmal nocturnal hemoglobinuria (PNH). In this study, we analyzed the amount of expression of a wide variety of GPI-AP in different subsets of hematopoietic cells present in normal peripheral blood (PB), to establish their normal patterns of expression and provide a frame of reference for the definition of the best combination of GPI-AP and PB cell subsets to be applied in the diagnosis and monitoring of PNH.

RESULTS

Our results show variable patterns of expression of different GPI-AP in distinct subsets of normal PB cells. Combined use of CD55 and CD59 represented the most useful dual-marker combination; however, its utility remained suboptimal for several subsets of leukocytes and for platelets.

CONCLUSIONS

For some cell subsets such as the neutrophils additional useful markers could be selected from a relatively broad panel (CD16/CD24/CD55/CD59/CD66b/CD157), whereas for other cell subsets the number of useful antigens was either restricted (monocytes: CD14/CD55/CD157; B cells: CD24/CD48/CD52/CD55; CD4+ T cells: CD48/CD52/CD55; eosinophils: CD55/CD59; CD8+ T cells: CD48/CD55) or limited to a single marker (CD48 on CD56low NK cells, CD55 on BDCA3- dendritic cells and CD56high NK cells, and CD59 for red cells), from all antigens analyzed.

Correlation between serum estradiol in the follicular phase of the ovarian cycle and decay acceleration factor (DAF) expression on red blood cells and coxsackiervirus B-3 induced hemagglutination in young cycling women

Decay accelerating factor (DAF) is a widely distributed glycoprotein which aids in the inactivation of complement. DAF is also a cellular receptor for certain group B coxsackieviruses (CVB) and is responsible for the viral hemagglutinating activity for human red blood cells (RBC). Healthy, young female volunteers donated blood on days 11 and 22 of the ovarian cycle. Samples were categorized into luteal and follicular phases based on serum progesterone level (P4 either < 2.0 ng/mL, follicular; P4 > or = 2.0 ng/mL, luteal) and analyzed by flow cytomtery for DAF expression on RBC and CD21 + B lymphocytes. Cycling females showed significant variation in CVB-induced hemagglutination and % RBC or CD19 + cells which were DAF +. There was a strong correlation between serum estradiol levels and % RBC expressing DAF (P < 0.01) in the follicular, but not in the luteal ovarian phase. Infection of white blood cells with green-fluorescent protein CVB (GFP-CVB) showed a correlation between infectivity of CD19+ cells and DAF expression. This indicates that women may show differential susceptibility to CVB infection in the luteal and follicular phases of the ovarian cycle.

Acquired and transient RBC CD55 deficiency (Inab phenotype) and anti-IFC

BACKGROUND

Antigens of the Cromer blood group system reside on the glycoprotein CD55 (decay-accelerating factor). The Inab phenotype is the null phenotype of this system. So far, only five propositi have been described who exhibit this phenotype, and single-nucleotide substitutions in the CD55 gene have been found in three of them. This report describes the first example of a patient with an acquired and transient form of the Inab phenotype.

CASE REPORT

A 54-year-old black patient was admitted to the hospital because of abdominal pain. Multiple splenic infarctions were visualized in the abdominal computerized tomography scan, and a prophylactic splenectomy was performed. The patient's serum reacted by an IAT with all donor RBCs tested.

RESULTS

Serologic analysis showed that the patient had the rare Inab phenotype and that his serum contained anti-IFC. Flow cytometry demonstrated the absence of CD55 on his RBCs, whereas lymphocytes, monocytes, granulocytes, and platelets expressed CD55, albeit at a weaker level than cells of common phenotypes. cDNA revealed no differences from the published sequences. Flow cytometry performed 12 months after splenectomy showed reappearance of the CD55 antigen; serologic tests performed after 17 months revealed that the anti-IFC had almost disappeared and that the RBCs were again agglutinated by various Cromer antibodies.

CONCLUSION

A patient with an acquired and transient form of the Inab phenotype is described, in whom the CD55 deficiency is limited to the RBCs and is associated with splenic infarctions.

Protein glycosylation: nature, distribution, enzymatic formation, and disease implications of glycopeptide bonds

Formation of the sugar-amino acid linkage is a crucial event in the biosynthesis of the carbohydrate units of glycoproteins. It sets into motion a complex series of posttranslational enzymatic steps that lead to the formation of a host of protein-bound oligosaccharides with diverse biological functions. These reactions occur throughout the entire phylogenetic spectrum, ranging from archaea and eubacteria to eukaryotes. It is the aim of this review to describe the glycopeptide linkages that have been found to date and specify their presence on well-characterized glycoproteins. A survey is also made of the enzymes involved in the formation of the various glycopeptide bonds as well as the site of their intracellular action and their affinity for particular peptide domains is evaluated. This examination indicates that 13 different monosaccharides and 8 amino acids are involved in glycoprotein linkages leading to a total of at least 41 bonds, if the anomeric configurations, the phosphoglycosyl linkages, as well as the GPI (glycophosphatidylinositol) phosphoethanolamine bridge are also considered. These bonds represent the products of N- and O-glycosylation, C-mannosylation, phosphoglycation, and glypiation. Currently at least 16 enzymes involved in their formation have been identified and in many cases cloned. Their intracellular site of action varies and includes the endoplasmic reticulum, Golgi apparatus, cytosol, and nucleus. With the exception of the Asn-linked carbohydrate and the GPI anchor, which are transferred to the polypeptide en bloc, the sugar-amino acid linkages are formed by the enzymatic transfer of an activated monosaccharide directly to the protein. This review also deals briefly with glycosidases, which are involved in physiologically important cleavages of glycopeptide bonds in higher organisms, and with a number of human disease states in which defects in enzymatic transfer of saccharides to protein have been implicated.

Early events in glycosylphosphatidylinositol anchor addition. substrate proteins associate with the transamidase subunit gpi8p

The addition of glycosylphosphatidylinositol (GPI) anchors to proteins occurs by a transamidase-catalyzed reaction mechanism soon after completion of polypeptide synthesis and translocation. We show that placental alkaline phosphatase becomes efficiently GPI-anchored when translated in the presence of semipermeabilized K562 cells but is not GPI-anchored in cell lines defective in the transamidase subunit hGpi8p. By studying the synthesis of placental alkaline phosphatase, we demonstrate that folding of the protein is not influenced by the addition of a GPI anchor and conversely that GPI anchor addition does not require protein folding. These results demonstrate that folding of the ectodomain and GPI addition are two distinct processes and can be mutually exclusive. When GPI addition is prevented, either by synthesis of the protein in the presence of cell lines defective in GPI addition or by mutation of the GPI carboxyl-terminal signal sequence cleavage site, the substrate forms a prolonged association with the transamidase subunit hGpi8p. The ability of the transamidase to recognize and associate with GPI anchor signal sequences provides an explanation for the retention of GPI-anchored protein within the ER in the absence of GPI anchor addition.

A standardized flow cytometric method for screening paroxysmal nocturnal haemoglobinuria (PNH) measuring CD55 and CD59 expression on erythrocytes and granulocytes

PNH is a disorder of the pluripotent stem cells resulting in a deficient expression of membrane-bound GPI-anchored proteins in different cell types. Several flow cytometric approaches are designed to detect this antigen deficiency. But they all require drawing and testing of normal samples as control. Therefore, in the present study two flow cytometric assays for the detection of CD55 and CD59 deficiency in erythrocytes (REDQUANT CD55/CD59) and granulocytes (CELLQUANT CD55/CD59) are proposed. Precalibrated beads are used to define the cut off between normal and deficient cell populations. The specificity of the tests has been evaluated in healthy blood donors (n=52) resulting in a clear and reproducible cut off (3%) for the normal percentage of GPI-deficient cells. This cut off has been confirmed in leukaemia and lymphoma patients not suspected for developing PNH. The sensitivity has been tested in patients suffering from known PNH (n=23). Both tests performed in combination allowed a reliable detection of PNH in all patients showing antigen deficiencies in both cell types in most patients (20/23). In contrast, the PNH clones in the investigated patients with MDS (4/19) or AA (4/22) were present in granulocytes or erythrocytes, only. This underlines the necessity of analysing erythrocytes as well as granulocytes. Preliminary data regarding a possible correlation between disease activity and percentage of antigen-deficient cells lead to the assumption that haemolytic crises can only be determined on granulocytes whereas deficient erythrocytes disappeared due to complement-mediated lysis of the PNH clone. In conclusion, the combination of the test kits enables the differential diagnosis of PNH clones in a standardized, simple and rapid approach which may have therapeutic consequences.