Advances in the creation of animal models of paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a disease caused by a phosphatidylinositol glycan anchor biosynthesis class A (PIG-A) mutation in hematopoietic stem cells. There are three theories about the possible mechanism of the pathogenesis of PNH: immune escape, anti-apoptotic mechanism, and secondary gene mutation. There has been little gain in the knowledge regarding its pathogenesis during the last decade owing to the lack of representative cell lines and animal models. There have been recent reports about the successful creation of PNH mouse and PNH rhesus macaque models. The detection of glycosylphosphatidylinositol-anchor protein (GPI-AP)-deficient cells and/or fluorescently labeled variant of aerolysin (FLAER) test, estimation of erythrocyte life span, and hemolysis-related experiments demonstrated that these animal models of PNH had GPI-AP-deficient blood cells with shortened lifespans and increased sensitivity to complement-activated hemolysis. However, there were no clinical manifestations such as hemolysis and thrombosis in these animal models. This suggested that the PIG-A mutation is one of the several conditions required for PNH, but it alone is not enough to cause PNH.

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.

Paroxysmal Nocturnal Hemoglobinuria: An Underestimated Cause of Pediatric Thromboembolism

Paroxysmal nocturnal hemoglobinuria (PNH) is a chronic disease caused by complement-mediated hemolysis. Clinical symptoms include intravascular hemolysis, nocturnal hemoglobinuria, thromboses, cytopenia, fatigue, abdominal pain, and a strong tendency toward bone marrow failure. It is a rare disease, especially in children, with high mortality rates without appropriate treatment.

We here present the case of a 17-year-old girl with unprovoked muscle vein thrombosis. Flow cytometric analysis showed deficiency of glycosyl-phosphatidylinositol-anchored membrane proteins on all three hematopoietic cell lines and confirmed the diagnosis of PNH. Treatment with the monoclonal antibody eculizumab achieved long-term remission.

As flow cytometry is normally not part of the routine diagnostics for pediatric thrombosis, awareness is crucial and PNH is important to consider in all children with thrombosis at atypical sites and abnormalities in blood counts with regard to hemolysis and cytopenia.

Significance of the detection of paroxysmal nocturnal hemoglobinuria clones in patients with multiple myeloma undergoing autologous stem cell transplantation

OBJECTIVE/BACKGROUND

There are reports about the presence of paroxysmal nocturnal hemoglobinuria (PNH) clones in multiple myeloma (MM), but these have been demonstrated only in red blood cells (RBCs) and the previous reports utilized an obsolete diagnostic method. We carried out a study to identify the clones by flow cytometry (FC) and to understand their clinical significance.

METHODS

A prospective study on consecutive patients with newly diagnosed MM who were candidates for autologous stem cell transplantation (ASCT) from 2008 to 2012. We screened peripheral blood samples by FC for CD55- and/or CD59-deficient RBC, neutrophils, and monocytes. PNH testing was carried out at diagnosis, before ASCT and 3 months after ASCT, as well as sporadically during MM remission and at disease relapse.

RESULTS

A total of 31 patients were included in the study. PNH clones reaching a median size of 10.8% (range 4.0-18.7%) were found in 10 patients (32.3%). Clones were detected at diagnosis in nine patients and 3 months after ASCT in one patient. A correlation between the presence of the clones and subclinical hemolysis was observed. Nevertheless, the presence of the clones did not influence the overall management and prognosis of the patients.

CONCLUSION

We confirmed findings of previous reports with current diagnostic guidelines and showed that although the size of the clones may be relatively large, their presence is probably not detrimental. The clinical significance of these clones and the possible mechanisms underlying their expansion in MM must be a subject of further investigation.

Human erythrocyte PIG-A assay: an easily monitored index of gene mutation requiring low volume blood samples

This laboratory has previously described a method for scoring the incidence of rodent blood Pig-a mutant phenotype erythrocytes using immunomagnetic separation in conjunction with flow cytometric analysis (In Vivo MutaFlow®). The current work extends this approach to human blood. The frequencies of CD59- and CD55-negative reticulocytes (RET(CD59-/CD55-)) and erythrocytes (RBC(CD59-/CD55-)) serve as phenotypic reporters of PIG-A gene mutation. Immunomagnetic separation was found to provide an effective means of increasing the number of reticulocytes and erythrocytes evaluated. Technical replicates were utilized to provide a sufficient number of cells for precise scoring while at the same time controlling for procedural accuracy by allowing comparison of replicate values. Cold whole blood samples could be held for at least one week without affecting reticulocyte, RET(CD59-/CD55-) or RBC(CD59-/CD55-) frequencies. Specimens from a total of 52 nonsmoking, self-reported healthy adult subjects were evaluated. The mean frequency of RET(CD59-/CD55-) and RBC(CD59-/CD55-) were 6.0 × 10(-6) and 2.9 × 10(-6), respectively. The difference is consistent with a modest selective pressure against mutant phenotype erythrocytes in the circulation, and suggests advantages of studying both populations of erythrocytes. Whereas intra-subject variability was low, inter-subject variability was relatively high, with RET(CD59-/CD55-) frequencies differing by more than 30-fold. There was an apparent correlation between age and mutant cell frequencies. Taken together, the results indicate that the frequency of human PIG-A mutant phenotype cells can be efficiently and reliably estimated using a labeling and analysis protocol that is well established for rodent-based studies. The applicability of the assay across species, its simplicity and statistical power, and the relatively non-invasive nature of the assay should benefit myriad research areas involving DNA damage, including studies of environmental factors that modify "spontaneous" mutation frequencies.

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.

Molecular Pathogenesis of Paroxysmal Nocturnal Hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH), although named for its marked fluctuations in the visibility of hemoglobinuria, is now classified as an acquired hematopoietic stem cell disorder. The clinical manifestations of PNH are very complicated, and include intravascular hemolytic anemia, venous thrombosis in unusual sites (abdomen, liver, cerebrum), deficient hematopoiesis, evolution to leukemia, and susceptibility to infection [1, 2]. The intravascular hemolysis is attributed to the enhanced susceptibility of erythrocytes to autologous complement [3]. The abnormal sensitivity is explained by a lack of complement regulatory membrane proteins such as decay-accelerating factor (DAF, CD55) and membrane inhibitor of reactive lysis (MIRL, CD59), which are covalently linked to the erythrocyte membrane through a glycosylphosphatidylinositol (GPI) anchor. The deficiency of the membrane proteins is caused by a synthetic defect in this anchor caused by impaired transfer of N- acetylglucosamine (GlcNAc) to phosphatidylinositol (PIns) [2]. Mutations of the phosphatidylinositol glycan class A (PIG-A) gene have been shown to contribute this abnormality in nearly all patients with PNH studied to date [4]. Recently, several reviews have been presented on various aspects of PNH [5-10]. This review focuses particularly on the recent elucidation of the molecular pathogenesis of GPI-anchor deficiency on PNH and related hematopoietic stem cell disorders.