Secreted IgM is predominantly found as pentameric molecules, but IgM can also be secreted as hexamers by B cell lines. Murine hexamers activate the complement cascade more efficiently than pentamers, ...but the physiologic significance of hexameric IgM remains unknown. Here, we report that IgM hexamers and pentamers are cleared from the circulation with similar kinetics, suggesting that the predominance of pentameric IgM in vivo reflects the regulation of polymer assembly and secretion in responding B cells. Normal IgM-secreting B cells, particularly those from the peritoneal cavity, are capable of secreting abundant hexameric IgM in vitro. The disparity between the ability of B cells to secrete IgM hexamers in vitro and the paucity of this polymer in vivo suggest that IgM hexamers might be deleterious. In support of this, we demonstrate that the autoantibodies from a number of patients with cold agglutinin (CA) disease include both IgM hexamers and pentamers. The CA IgM hexamers lyse human erythrocytes in the presence of human complement more efficiently than CA IgM pentamers, suggesting a potential role for hexameric IgM in the pathogenesis of this autoimmune syndrome.
We have characterized the erythrocytes, granulocytes, and platelets of 54 patients with paroxysmal nocturnal hemoglobinuria (PNH) with antibodies to glycosylphosphatidylinositol-anchored proteins ...(anti-CD55, anti-CD59, and anti-CD16) and flow cytometry to establish the usefulness of this technique in the diagnosis of this disorder. All patients demonstrated either completely (PNH III) or partially (PNH II) deficient red cells and granulocytes. Anti-CD59 best demonstrated PNH II red cells, which were present in 50% of the patients. The proportion of abnormal granulocytes was usually greater than the proportion of abnormal red cells; 37% of the patients had >80% abnormal granulocytes. Anti-CD55 did not delineate the erythrocyte populations as well as did anti-CD59. Either anti-CD55 or anti-CD59 could be used equally well to analyze granulocytes; anti-CD16 did not demonstrate cells of partial deficiency. Platelets could not be used for detailed analysis as the normal and abnormal populations were not well distinguished. Flow cytometry of erythrocytes using anti-CD59 or of granulocytes using either anti-CD55 or anti-CD59 provides the most accurate technique for the diagnosis of paroxysmal nocturnal hemoglobinuria; it is clearly more specific, more quantitative, and more sensitive than the tests for PNH that depend upon hemolysis by complement (the acidified serum lysis Ham test, the sucrose lysis test, and the complement lysis sensitivity CLS test).
Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired, clonal disorder of hematopoietic cells caused by somatic mutation in the X-linked PIGA gene encoding a protein involved in the synthesis of ...the glycosylphosphatidylinositol (GPI) anchor by which many proteins are attached to the membrane of cells. About 15 proteins have been found to be lacking or markedly deficient on the abnormal blood cells. These defects result in a clinical syndrome that includes intravascular hemolysis mediated by complement, unusual venous thromboses, deficits of hematopoiesis, and other manifestations. Therapy is presently directed mainly at the consequences of the disorder rather than its basic causes and includes replacement of iron, folic acid, and whole blood; hormonal modulation (prednisone, androgens); anticoagulation; and bone marrow transplantation. PNH is a chronic disease with more than half of adult patients surviving 15 years or more; prognosis is less good in children.
Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal hematologic disorder characterized by hemoglobinuria, thrombosis, infection, and a tendency toward bone marrow aplasia. Onset usually ...occurs in adulthood. Few children and adolescents with PNH have been described, and data on diagnosis, clinical course, and survival in young patients are unavailable.
We retrospectively reviewed clinical and laboratory data on all patients 21 years old or younger in whom PNH had been diagnosed at Duke University Medical Center from 1966 to 1991.
Medical records and clinical follow-up data were available for 26 young patients. Although 50 percent of adult patients present with hemoglobinuria, only four of our patients (15 percent) presented with this feature. In contrast, 15 of our patients (58 percent) had moderate or severe bone marrow failure at presentation, as compared with about 25 percent of adults in cases from the literature; all 26 patients eventually had evidence of bone marrow dysfunction. Eight patients (31 percent) have died, with a median survival of 13.5 years since their initial symptoms.
Children and adolescents with PNH have a greater prevalence of bone marrow failure than do adults with this disorder, and their morbidity and mortality are high. Bone marrow transplantation should be considered for selected young patients with PNH.
The gene for CD59 membrane inhibitor of reactive lysis (MIRL), protectin, a phosphatidylinositol-linked surface glycoprotein that regulates the formation of the polymeric C9 complex of complement and ...that is deficient on the abnormal hematopoietic cells of patients with paroxysmal nocturnal hemoglobinuria, consists of four exons spanning 20 kilobases. The untranslated first exon is preceded by a G+C-rich promoter region that lacks a consensus TATA or CAAT motif. The second exon encodes the hydrophobic leader sequence of the protein, and the third exon encodes the aminoterminal portion of the mature protein. The fourth exon encodes the remainder of the mature protein, including the hydrophobic sequence necessary for glycosyl-phosphatidylinositol anchor attachment. The structure of the CD59 gene is very similar to that encoding Ly-6, a murine glycoprotein with which CD59 has some structural similarity. The striking similarity in gene structure is further evidence that the two proteins belong to a superfamily of proteins that may also include the urokinase plasminogen-activator receptor and a squid glycoprotein of unknown function.
Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal hematopoietic stem cell disorder characterized by complement-mediated hemolysis due to deficiencies of glycosylphosphatidylinositol-anchored ...proteins (GPI-APs) in subpopulations of blood cells. Acquired mutations in the X-linked phosphatidylinositol glycan–class A (PIG-A) gene appear to be the characteristic and pathogenetic cause of PNH. To develop a gene therapy approach for PNH, a retroviral vector construct, termed MPIN, was made containing the PIG-A complementary DNA along with an internal ribosome entry site and the nerve growth factor receptor (NGFR) as a selectable marker. MPIN transduction led to efficient and stable PIG-A and NGFR gene expression in a PIG-A–deficient B-cell line (JY5), a PIG-A–deficient K562 cell line, an Epstein-Barr virus–transformed B-cell line (TK-14−) established from a patient with PNH, as well as peripheral blood (PB) mononuclear cells from a patient with PNH. PIG-A expression in these cell lines stably restored GPI-AP expression. MPIN was transduced into bone marrow mononuclear cells from a patient with PNH, and myeloid/erythroid colonies and erythroid cells were derived. These transduced erythroid cells restored surface expression of GPI-APs and resistance to hemolysis. These results indicate that MPIN is capable of efficient and stable functional restoration of GPI-APs in a variety of PIG-A–deficient hematopoietic cell types. Furthermore, MPIN also transduced into PB CD34+ cells from a normal donor, indicating that MPIN can transduce primitive human progenitors. These findings set the stage for determining whether MPIN can restore PIG-A function in multipotential stem cells, thereby providing a potential new therapeutic option in PNH.
Abstract 3480
Paroxysmal nocturnal hemoglobinuria (PNH) is a chronic and life-threatening hematopoietic stem cell disorder characterized by uncontrolled complement-mediated hemolysis. PNH, in large ...part due to chronic hemolysis and platelet hyperactivation, is associated with thromboembolism (TE), one of the leading causes of disease mortality. Eculizumab, a monoclonal antibody that inhibits terminal complement activation, has been shown in clinical trials to reduce hemolysis and the incidence of TE. The International PNH Registry provides the opportunity to understand from real world experience the impact of eculizumab on TE reduction in PNH patients.
To assess the risk factors for TE and mortality in PNH patients enrolled in the Registry and to assess the effectiveness of eculizumab in reducing PNH-associated TEs.
Patients are eligible for the Registry if they have a detectable PNH clone, regardless of disease severity, comorbidities, or treatments (past, current or planned). As of June 30, 2012, there were 1547 patients enrolled from 25 countries on 5 continents. Patients were excluded from analysis if they were missing key demographic variables or dates of eculizumab use, or did not yet have follow-up information. The cumulative incidence of TE was determined using competing risks methods to take into account bone marrow transplantation and death, while Kaplan-Meier methods were used for the cumulative incidence of mortality. Risk factors for TE and mortality were explored using a Cox proportional hazards model with stepwise selection (the significance level was relaxed to P=0.20 due to the small number of events for analysis). Variables examined in the models included: ethnicity; prior TEs, bone marrow disorders, impaired renal function, impaired hepatic function (IHF), abdominal pain, dysphagia, dyspnea, easy bruising/bleeding, fatigue, headache, hemoglobinuria, Karnofsky performance score, granulocyte clone size and lactate dehydrogenase (LDH) at enrollment, red blood cell (RBC) transfusions 6 months prior to enrollment as a marker for hemolysis, and treatments after enrollment (eculizumab and warfarin/heparin).
The mean age of the 1047 patients eligible for analysis was 45 years; 537 patients (51.3%) were female and 868 were Caucasian (82.9%). Anti-coagulants (heparin/warfarin) were used by 28% of patients and eculizumab was used by 51% during follow-up (18% used both). During a mean (SD) follow-up of 22.5 (18.4) months, 16 patients had a TE and 51 were deceased. Patients taking eculizumab during follow-up had a cumulative incidence of TE at 1 year of 0.41% and 1.35% at 2 years, while patients not taking eculizumab had TE incidence of 1.70% and 2.61% at 1 and 2 years, respectively. In the multivariate Cox model, the greatest associations with TE were RBC transfusions in the 6 months before enrollment (hazard ratio HR=9.61), history of IHF (HR=4.78), dyspnea (HR=2.42) and headache (HR=2.33) at enrollment. While controlling for these variables, eculizumab had a significant protective effect (HR=0.23, 95% CI = 0.08–0.66). The cumulative incidence of mortality in eculizumab-treated patients was 2.31% and 4.21% at 1 and 2 years, while in untreated patients it was 4.40% and 7.01%, respectively. In the multivariate model of mortality, the greatest associations were age 60+ years (HR=4.72), Karnofsky score <80 (HR=2.34), fatigue at enrollment (HR=1.94), and recent RBC transfusion (HR=1.75). While controlling for these variable, eculizumab had a significant protective effect (HR=0.41, 95% CI = 0.23–0.73).
This analysis of a large international cohort of ‘real world' patients with PNH showed that eculizumab is associated with a significantly reduced risk of TE and mortality, consistent with prior research. Recent RBC transfusion, a surrogate marker for hemolysis, was associated with increased risk of TE and mortality. Several symptoms and hepatic dysfunction also showed increased risks for these outcomes. As might be expected, older age and low performance status were associated with mortality. These data should be interpreted within the context of a contemporary cohort of PNH patients who may or may not be treated (with either eculizumab and/or anticoagulation). These analyses are limited due to small number of TE and mortality outcomes.
Muus:Alexion Pharmaceuticals : Sat on advisory board of Alexion Pharmaceuticals. Other. Urbano-Ispizua:Alexion Pharmaceuticals, Inc: Membership on an entity’s Board of Directors or advisory committees. Maciejewski:NIH: Research Funding; Aplastic Anemia&MDS International Foundation: Research Funding. Kanakura:Shire: Consultancy. Rosse:Alexion Pharmaceuticals, Inc: Consultancy, Membership on an entity’s Board of Directors or advisory committees. Khursigara:Alexion Pharmaceuticals, Inc: Employment. Bedrosian:Alexion Pharmaceuticals: Employment, Equity Ownership. Hillmen:Alexion Pharmaceuticals, Inc: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees.
ABSTRACT
Although paroxysmal nocturnal hemoglobinuria (PNH) is often associated with aplastic anemia (AA), the nature of the pathogenetic link between PNH and AA remains unclear. Moreover, the PIG-A ...mutation appears to be necessary but not sufficient for the development of PNH, suggesting other factors are involved. The ability of PNH marrow cells to form
in vitro hematopoietic colonies and the ability of PNH marrow to generate stroma that could support hematopoiesis of normal or PNH marrow in cross culture were investigated. PNH marrow from both post-Ficoll and post-lineage depleted hematopoietic progenitor cells grew similarly significantly fewer colonies than normal marrow. Sorting of CD59
+ and CD59
− CD34
+ CD38
− cells from patients with PNH showed similarly impaired clonogenic efficiency, indicating that the hematopoietic defect in PNH does not directly relate to GPI-anchored protein expression. PNH marrow readily grew stroma similar to marrow from normal donors. Cross culture experiments revealed that PNH stroma appears to function normally
in vitro; it can support growth of normal marrow cells as well as normal stroma does, but neither PNH nor normal stroma could support the growth of PNH marrow cells. The hematopoietic defect in PNH is not due to defective stroma, but is due to defective progenitor cell growth related to additional unknown factors.
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