High frequency of several PIG-A mutations in patients with aplastic anemia and myelodysplastic syndrome

Benchmark dose estimation among benzene-exposed workers in China: Based on quantitative multi-endpoint genotoxicity assessments

Based on previous exposure studies, benzene (BZ) has been classified as a human carcinogen and occupational exposure limit (OELs) to BZ has been set to be about 1 ppm around the world. However, health hazards have still been reported with exposure below the OEL. Thus, the OEL needs to be updated to reduce health risk. The overall aim of our study was therefore to generate new OEL for BZ via a benchmark dose (BMD) approach and based on quantitative and multi-endpoint genotoxicity assessments. Genotoxicities were determined using the novel human PIG-A gene mutation assay, the micronucleus (MN) test and the COMET assay in benzene-exposed workers. Among the 104 workers with below current OELs, they exhibited significantly higher PIG-A mutant frequencies (MFs) (15.96 ± 14.41 × 10^-6) and MN frequencies (11.55 ± 6.83‰) than among the general subjects (PIG-A MFs: 5.45 ± 4.56 × 10^-6, MN frequencies: 4.51 ± 1.58‰), but no difference in the COMET assay. A significant association was also observed between BZ exposures and PIG-A MFs and MN frequencies (P < 0.001). Our results indicate that health hazards were induced among workers with below OEL exposures. Based on results from the PIG-A and MN assays, the lower confidence limit of the BMD (BMDL) were calculated to be 8.71 mg/m³-year and 0.44 mg/m³-year, respectively. Based on these calculations, the OEL for BZ was determined to be lower than 0.07 ppm. This value can be considered by regulatory agencies to set new exposure limits and to better protect workers.

Immunophenotypic assessment of PNH clones in major and minor cell lineages in the peripheral blood of patients with paroxysmal nocturnal hemoglobinuria

BACKGROUND

Flow cytometric immunophenotyping is essential for the diagnosis of paroxysmal nocturnal hemoglobinuria (PNH). Most cases have easy to interpret flow cytometry profiles with red cells, neutrophils and monocytes showing complete deficiency of glycophosphatidylinositol (GPI) linked antigen expression. Some cases are more challenging to interpret due to the presence of multiple populations of PNH cells and variable levels of GPI antigen expression.

METHODS

We studied 46 known PNH patients, many with complex immunophenotypic profiles using a novel, single tube, multi-parameter 7-color immunophenotyping assay that allowed simultaneous detection and assessment of PNH clones within multiple lineages of peripheral blood leucocytes. Red cell PNH clones were also assessed in total and immature (CD71+) components by CD59 expression.

RESULTS

For individual patients, total PNH clones in each cell lineage were highly correlated. Monocytes, eosinophils and basophils showed the highest proportions of PNH cells. Red cell PNH clones were typically smaller than monocyte and neutrophil PNH clones. In most cases, PNH clones were detectable in minor leucocyte populations where multiple populations of PNH cells were present, variability in the proportions of type II and type III cells was seen across different cell lineages, even though total PNH clones remained similar.

CONCLUSIONS

This study shows that PNH patients with multiple PNH clones do not always display the same abnormality across all cell lineages routinely tested. There is no simple explanation for this but is likely due to a combination of complex molecular, genetic and biochemical dysfunction in different blood cell types.

Mutagenicity monitoring in humans: Global versus specific origin of mutations

An underappreciated aspect of human mutagenicity biomonitoring is tissue specificity reflected in different assays, especially those that measure events that can only occur in developing bone marrow (BM) cells. Reviewed here are 9 currently-employed human mutagenicity biomonitoring assays. Several assays measure chromosome-level events in circulating T-lymphocytes (T-cells), i.e., traditional analyses of aberrations, translocation studies involving chromosome painting and fluorescence in situ hybridization (FISH) and determinations of micronuclei (MN). Other T-cell assays measure gene mutations. i.e., hypoxanthine-guanine phosphoriboslytransferase (HPRT) and phosphoribosylinositol glycan class A (PIGA). In addition to the T-cell assays, also reviewed are those assays that measure events in peripheral blood cells that necessarily arose in BM cells, i.e., MN in reticulocytes; glycophorin A (GPA) gene mutations in red blood cells (RBCs), and PIGA gene mutations in RBC or granulocytes. This review considers only cell culture- or cytometry-based assays to describe endpoints measured, methods, optimal sampling times, and sample summaries of typical quantitative and qualitative results. However, to achieve its intended focus on the target cells where events occur, kinetics of the cells of peripheral blood that derive at some point from precursor cells are reviewed to identify body sites and tissues where the genotoxic events originate. Kinetics indicate that in normal adults, measured events in T-cells afford global assessments of in vivo mutagenicity but are not specific for BM effects. Therefore, an agent's capacity for inducing mutations in BM cells cannot be reliably inferred from T-cell assays as the magnitude of effect in BM, if any, is unknown. By contrast, chromosome or gene level mutations measured in RBCs/reticulocytes or granulocytes must originate in BM cells, i.e. in RBC or granulocyte precursors, thereby making them specific indicators for effects in BM. Assays of mutations arising directly in BM cells may quantitatively reflect the mutagenicity of potential leukemogenic agents.

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.

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.

Progressive genomic instability in the Nup98-HoxD13 model of MDS correlates with loss of the PIG-A gene product

The Nup98-HoxD13 (NHD13) fusion gene was identified in a patient with therapy-related myelodysplastic syndrome (MDS). When transgenically expressed in hematopoietic cells, mice faithfully recapitulate human disease with serial progression from peripheral blood (PB) cytopenias and increased bone marrow (BM) blasts to acute leukemia. It is well accepted that genomic instability in dysplastic hematopoietic stem/progenitor cells (HSPC) drives the evolution of MDS to acute leukemia. Findings here demonstrate that reticulocytes, myeloid and lymphoid PB cells of NHD13 mice, display an increase in the age-associated loss of glycosylphosphatidylinositol-linked surface proteins versus wild type controls. These data correlate with a progressive increase in the DNA damage response as measured by γ-H2AX activity, accumulating BM blasts as the disease progresses and finally development of acute leukemia. These findings clearly demonstrate a state of progressive genomic instability that increases the likelihood of a “second hit” or complimentary mutation later in the disease to trigger development of acute leukemia and underscores the mechanistic nature of how the NUP98-HoxD13 transgene induces progression of MDS to acute leukemia. Additionally, these data support the use of the PIG-A assay as an efficient, real-time surrogate marker of the genomic instability that occurs in the MDS HSPCs.

Key Point

The PIG-A assay is a sensitive, nonlethal method for the serial assessment of genomic instability in mouse models of MDS.

3'UTR-truncated Hmga2 cDNA causes MPN-like hematopoiesis by conferring a clonal growth advantage at the level of HSC in mice

Overexpression of high mobility group AT-hook 2 (HMGA2) is found in a number of benign and malignant tumors, including the clonal PIGA(-) cells in 2 cases of paroxysmal nocturnal hemoglobinuria (PNH) and some myeloproliferative neoplasms (MPNs), and recently in hematopoietic cell clones resulting from gene therapy procedures. In nearly all these cases overexpression is because of deletions or translocations that remove the 3' untranslated region (UTR) which contains binding sites for the regulatory micro RNA let-7. We were therefore interested in the effect of HMGA2 overexpression in hematopoietic tissues in transgenic mice (ΔHmga2 mice) carrying a 3'UTR-truncated Hmga2 cDNA. ΔHmga2 mice expressed increased levels of HMGA2 protein in various tissues including hematopoietic cells and showed proliferative hematopoiesis with increased numbers in all lineages of peripheral blood cells, hypercellular bone marrow (BM), splenomegaly with extramedullary erythropoiesis and erythropoietin-independent erythroid colony formation. ΔHmga2-derived BM cells had a growth advantage over wild-type cells in competitive repopulation and serial transplantation experiments. Thus overexpression of HMGA2 leads to proliferative hematopoiesis with clonal expansion at the stem cell and progenitor levels and may account for the clonal expansion in PNH and MPNs and in gene therapy patients after vector insertion disrupts the HMGA2 locus.

3'UTR-truncated Hmga2 cDNA causes MPN-like hematopoiesis by conferring a clonal growth advantage at the level of HSC in mice

Overexpression of high mobility group AT-hook 2 (HMGA2) is found in a number of benign and malignant tumors, including the clonal PIGA(-) cells in 2 cases of paroxysmal nocturnal hemoglobinuria (PNH) and some myeloproliferative neoplasms (MPNs), and recently in hematopoietic cell clones resulting from gene therapy procedures. In nearly all these cases overexpression is because of deletions or translocations that remove the 3' untranslated region (UTR) which contains binding sites for the regulatory micro RNA let-7. We were therefore interested in the effect of HMGA2 overexpression in hematopoietic tissues in transgenic mice (ΔHmga2 mice) carrying a 3'UTR-truncated Hmga2 cDNA. ΔHmga2 mice expressed increased levels of HMGA2 protein in various tissues including hematopoietic cells and showed proliferative hematopoiesis with increased numbers in all lineages of peripheral blood cells, hypercellular bone marrow (BM), splenomegaly with extramedullary erythropoiesis and erythropoietin-independent erythroid colony formation. ΔHmga2-derived BM cells had a growth advantage over wild-type cells in competitive repopulation and serial transplantation experiments. Thus overexpression of HMGA2 leads to proliferative hematopoiesis with clonal expansion at the stem cell and progenitor levels and may account for the clonal expansion in PNH and MPNs and in gene therapy patients after vector insertion disrupts the HMGA2 locus.

Low concentration of serum haptoglobin has impact on understanding complex pathophysiology in patients with acquired bone marrow failure syndromes

To clarify whether measurement of serum haptoglobin (Hp) has impact on understanding pathophysiology in bone marrow failure (BMF) syndromes, we investigated concentrations of serum Hp by nephelometric procedure in 156 Japanese patients with BMF, including 54 aplastic anemia (AA), 50 paroxysmal nocturnal hemoglobinuria (PNH), and 52 myelodysplastic syndromes (MDS) patients. The frequencies with low concentrations of serum Hp (<42 mg/dL) in PNH patients (98.0%) were significantly higher than those in AA (27.8%; P < 0.0001) and MDS (38.5%; P < 0.0001) patients. In AA patients, white blood cell (WBC), absolute neutrophil, and platelet counts were significantly decreased in the group (n = 15) with low concentrations of serum Hp than in that (n = 39) with normal concentrations of it, and WBC counts were positively correlated with concentrations of serum Hp, suggesting that WBC counts may affect the concentrations. In MDS patients, hemoglobin concentrations and serum iron were significantly decreased and increased, respectively, in the group (n = 20) with low concentrations of serum Hp than in that (n = 32) with normal concentrations of it, and the values of serum iron were inversely correlated with concentrations of serum Hp, suggesting that ineffective erythropoiesis may affect the concentrations. Several AA and MDS patients with low concentrations of serum Hp had Coombs-negative autoimmune hemolytic anemia determined by immunoradiometric assay. In conclusion, several factors in conjunction with pathophysiology contribute to decrease of serum Hp in BMF.

Detection of paroxysmal nocturnal hemoglobinuria clones in patients with myelodysplastic syndromes and related bone marrow diseases, with emphasis on diagnostic pitfalls and caveats

BACKGROUND

The presence of paroxysmal nocturnal hemoglobinuria clones in the setting of aplastic anemia or myelodysplastic syndrome has been shown to have prognostic and therapeutic implications. However, the status of paroxysmal nocturnal hemoglobinuria clones in various categories of myelodysplastic syndrome and in other bone marrow disorders is not well-studied.

DESIGN AND METHODS

By using multiparameter flow cytometry immunophenotypic analysis with antibodies specific for four glycosylphosphatidylinositol-anchored proteins (CD55, CD59, CD16, CD66b) and performing an aerolysin lysis confirmatory test in representative cases, we assessed the paroxysmal nocturnal hemoglobinuria-phenotype granulocytes in 110 patients with myelodysplastic syndrome, 15 with myelodysplastic/myeloproliferative disease, 5 with idiopathic myelofibrosis and 6 with acute myeloid leukemia.

RESULTS

Paroxysmal nocturnal hemoglobinuria-phenotype granulocytes were detected in nine patients with low grade myelodysplastic syndrome who showed clinicopathological features of bone marrow failure, similar to aplastic anemia. All paroxysmal nocturnal hemoglobinuria-positive cases demonstrated loss of the four glycosylphosphatidylinositol-anchored proteins, with CD16(-)CD66b(-) clones being larger than those of CD55(-)CD59(-) (p<0.05). Altered glycosylphosphatidylinositol-anchored protein expression secondary to granulocytic hypogranulation, immaturity, and/or immunophenotypic abnormalities was present in a substantial number of cases and diagnostically challenging.

CONCLUSIONS

These results show that routine screening for paroxysmal nocturnal hemoglobinuria clones in patients with an intrinsic bone marrow disease who show no clinical evidence of hemolysis has an appreciable yield in patients with low grade myelodysplastic syndromes. The recognition of diagnostic caveats and pitfalls associated with the underlying intrinsic bone marrow disease is essential in interpreting paroxysmal nocturnal hemoglobinuria testing correctly. In our experience, the CD16/CD66b antibody combination is superior to CD55/CD59 in screening for subclinical paroxysmal nocturnal hemoglobinuria because it detects a large clone size and is less subject to analytical interference.

Detection of CD55- and CD59-deficient granulocytic populations in patients with myelodysplastic syndrome

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by absence of CD55 and CD59 from the surface of affected cells. PNH has been associated with myelodysplastic syndromes (MDS). The aim of our study was to estimate the prevalence of the PNH clone in MDS patients by detecting CD55 and CD59 deficiency. We studied 90 MDS patients: 19 patients with RA, 15 with refractory anemia with ringed sideroblasts (RARS), 18 with refractory anemia with excess of blasts (RAEB), 17 with refractory anemia with excess of blasts in transformation (RAEB-t), and 21 with chronic myelomonocytic leukemia (CMML). Twenty healthy individuals were also studied as the control group. We studied the PNH clone on granulocytes of these patients with the aid of flow cytometry. CD55- and CD59-deficient granulocytic populations were detected in 15.5% of MDS patients compared to 2.8% of normal individuals. Among the subgroups of the study, significant difference was present in three cases: (1) between CMML and control, (2) between CMML and RA, and (3) between CMML and RARS. These data indicate a possible association between PNH phenotype and MDS. MDS patients of worse prognosis (CMML) express more strongly the PNH clone compared to those of better prognosis (RA and RARS). Perhaps, the examination of MDS patients for the PNH clone by flow cytometry could provide us with a valuable prognostic tool.

Microvascular thrombosis in the hepatic vein of a patient with paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by complement-mediated hemolysis, venous thrombosis, and bone marrow failure. In May 2003, a 33-year-old man was admitted to a hospital with right hypochondralgia and fever. He had a history of aplastic anemia. The patient's diagnosis of diffuse microvessel thrombosis in the hepatic vein due to an unknown cause was derived from the findings of a contrast-enhanced computed tomography examination of the abdominal region, angiographic evaluation of abdominal vessels, and pathohistologic examination of a liver biopsy sample. The patient was subsequently treated with warfarin. The abdominal pain and fever continued, however, and anemia gradually appeared. In April 2004, the patient was referred to our hospital to examine the cause of the thrombosis. On admission, slight anemia and a low serum haptoglobin level were observed. A flow cytometry evaluation of CD55 and/or CD59, CD59, and CD48 expression in erythrocytes, granulocytes, and monocytes, respectively, showed that the respective proportions of negative populations were 5.6%, 97.1%, and 96.2%. The patient then received a diagnosis of aplastic anemia/PNH syndrome, which had caused the hemolytic anemia and thrombosis, although no hemoglobinuria had been observed during his clinical course. This patient is, to our knowledge, the first reported case of a PNH patient with thrombosis present only in hepatic microvessels and not in hepatic large vessels, in spite of the presence of few hemolytic events.

Autoimmunity and malignancy in hematology—More than an association

Several associations between hematological malignancies and autoimmunity directed against hematopoietic cells exist. Antibody mediated elimination of mature blood cells such as autoimmune hemolytic anemia (AIHA) and immune thrombocytopenia (ITP) are frequent complications of non-Hodgkin lymphomas, most prominently chronic lymphocytic leukemia. Autoimmunity directed against hematopoietic precursor cells is the hallmark of aplastic anemia, but many features of this disease are shared by two related disorders, paroxysmal nocturnal hemoglobinuria (PNH) and myelodysplastic syndrome (MDS). While the clinical associations between hematological malignancy and autoimmunity have been described many decades ago, only in the last several years have the common pathogenetic mechanisms been elucidated. We summarize the recent progress made in understanding how hematological malignancy gives rise to autoimmunity directed against blood cells and vice versa, and illustrate parallels in the etiology of malignant and autoimmune hematological disorders. Specifically, recent progress in the recognition of the association of lymphoproliferative disorders and autoimmunity against mature blood cells, and common pathogenetic background of aplastic anemia, paroxysmal nocturnal hemoglobinuria, and myelodysplastic syndrome are discussed.

Cyclosporine therapy for acquired aplastic anemia: predictive factors for the response and long-term prognosis

Although cyclosporine (CsA) is a key drug in the treatment of acquired aplastic anemia (AA), the role of single-agent therapy with CsA remains unclear. To determine the efficacy of CsA in the treatment of AA, we treated 38 AA patients with CsA alone and followed up the patients for 6 months to 16 years. Twenty patients (53%) achieved either a partial or complete remission within 1 year of starting CsA therapy. Thirteen (81%) of 16 patients who showed an increase in the reticulocyte count of >20 x 10(9)/L within 2 months achieved remission, whereas the response rate was only 32% in patients who failed to show such an increase in the reticulocyte count. The actuarial overall survival and failure-free survival rates at 5 years were 91% and 37%, respectively. These data indicate that CsA alone can achieve a sustained remission in approximately 40% of AA patients, with a low probability of inducing secondary clonal diseases. Given its low toxicity and because the effectiveness of CsA can be judged within 2 months of therapy, CsA may be the first drug of choice at outpatient clinics for AA patients not requiring transfusions.

The role of Wilms' tumor gene peptide-specific cytotoxic T lymphocytes in immunologic selection of a paroxysmal nocturnal hemoglobinuria clone

OBJECTIVE

To clarify an expansion mechanism of a paroxysmal nocturnal hemoglobinuria (PNH) clone with the Wilms' tumor gene (WT1).

MATERIALS AND METHODS

In PNH patients with the HLA-A*2402 allele, frequencies of peripheral blood (PB) WT1 peptide-specific and HLA-A*2402-restricted CD8+ cells and WT1 peptide-stimulated interferon-gamma-producing mononuclear cells (MNCs), cytotoxicity of WT1 peptide-specific and HLA-A*2402-restricted cytotoxic T lymphocyte (CTL) clone (TAK-1) cells on bone marrow (BM) MNCs, and after co-incubation with TAK-1 cells, changes in colony-forming unit granulocyte-macrophage colony formation of CD34+ cells and in CD59 expression in viable CD34+ cells were investigated.

RESULTS

The frequencies of PB WT1 peptide-specific and HLA-A*2402-restricted CD8+ cells (p < 0.005) and WT1 peptide-stimulated interferon-gamma-producing MNCs (p < 0.02) were significantly higher in 5 PNH patients than 8 healthy volunteers (HV). In 5 PNH patients or 3 HV, TAK-1 cells significantly killed BMMNCs and suppressed colony formations of CD34+CD59+ and/or CD34+CD59- cells in the absence and presence of a WT1 peptide or only in the presence of the peptide, respectively, in an HLA-restricted manner. After co-incubation with TAK-1 cells, reduction rates of colony formation of CD34+CD59- cells were significantly less than those of CD34+CD59+ cells in 5 PNH patients (p < 0.002) and proportions of viable CD34+CD59- cells from 5 PNH patients significantly increased in the absence (p < 0.01) and presence (p < 0.01) of a WT1 peptide in an HLA-restricted manner.

CONCLUSION

WT1 peptide-specific and HLA-restricted CTLs may play an important role in expansion of a PNH clone during immunologic selection and/or in the occurrence of BM failure via interferon-gamma in PNH.