Paroxysmal nocturnal hemoglobinuria: stem cells and clonality

Hallmarks of stemness in mammalian tissues

All adult tissues experience wear and tear. Most tissues can compensate for cell loss through the activity of resident stem cells. Although the cellular maintenance strategies vary greatly between different adult (read: postnatal) tissues, the function of stem cells is best defined by their capacity to replace lost tissue through division. We discuss a set of six complementary hallmarks that are key enabling features of this basic function. These include longevity and self-renewal, multipotency, transplantability, plasticity, dependence on niche signals, and maintenance of genome integrity. We discuss these hallmarks in the context of some of the best-understood adult stem cell niches.

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.

A Pig-a conditional knock-out mice model mediated by Vav-iCre: stable GPI-deficient and mild hemolysis

Paroxysmal nocturnal hemoglobinuria is a clonal disease caused by PIG-A mutation of hematopoietic stem cells. At present, there is no suitable PNH animal model for basic research, therefore, it is urgent to establish a stable animal model. We constructed a Pig-a conditional knock-out mice model by ES targeting technique and Vav-iCre. The expressions of GPI and GPI-AP were almost completely absent in CKO homozygote mice, and the proportion of the deficiency remained stable from birth. In CKO heterozygote mice, the proportion of the deficiency of GPI and GPI-AP was partially absent and decreased gradually from birth until it reached a stable level at 3 months after birth and remained there for life. Compared with normal C57BL/6N mice and Flox mice, pancytopenia was found in CKO homozygous mice, and leukopenia and anemia were found in CKO heterozygotes mice. Meanwhile, in CKO mice, the serum LDH, TBIL, IBIL, complement C5b-9 levels were increased, and the concentration of plasma FHb was increased. Hemosiderin granulosa cells can be seen more easily in the spleens of CKO mice. What's more, CKO mice had stable transcription characteristics. In conclusion, our mouse model has stable GPI-deficient and mild hemolysis, which may be an ideal in vivo experimental model for PNH.

Markers of Thrombin Generation and Inflammation in Patients with Paroxysmal Nocturnal Hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) presents with intravascular hemolysis, bone marrow failure and thrombosis. Various studies have reported geographic and ethnic variation in prevalence of thrombosis in PNH. There is limited data on thrombosis in PNH from the Indian subcontinent. In this study we describe disease burden and risk factors for thrombosis in 18 Indian PNH patients. We studied markers of thrombin generation (Thrombin-antithrombin complexes; TAT and D-Dimer), endothelium and platelet activation (soluble P-selectin) and inflammation (interleukin-6; IL-6) in PNH patients and compared their levels with healthy controls. Thrombosis was identified in 17% of PNH patients. TAT, sP-selectin and D-Dimer levels were significantly elevated in PNH patients (TAT: 5.06 ± 1.08 ng/ml; sP-selectin: 80.57 ± 19.5 ng/ml; D-Dimer mean: 936 ng/ml 95% CI 559, 1310) compared to control population (TAT: 3.39 ± 0.769 ng/ml P = 0.016; sP-selectin: 44.67 ± 5.17 ng/ml P = 0.002). Using Youden's J statistic, the cut-off values for TAT and sP-selectin in our cohort of PNH patients were 2.90 ng/ml and 58.41 ng/ml respectively. TAT, sP-selectin and D-Dimer levels were elevated beyond the cut-off values in PNH patients with thrombosis compared to those without thrombosis. A positive correlation was noted between TAT, sP-selectin and D-Dimer levels. Increased TAT, sP-selectin, and D-Dimer levels may indicate impending thrombosis in PNH.

Abnormal expression and mutation of the RBPJ gene may be involved in CD59- clonal proliferation in paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal proliferative disease of hematopoietic stem cells. Various gene mutations, including the phosphatidylinositol glycan anchor biosynthesis class A (PIG-A) gene, may contribute to the proliferation of PNH clones. In order to explore the mechanism of PNH clone proliferation, a study was performed on 13 patients with PNH who underwent whole exome sequencing. The frequency of mutations in these patients was explored, and an additional 30 patients with PNH were selected for analysis of cluster of differentiation 59-negative (CD59^-) cells. The mRNA expression of 13 genes, which were selected based on their high frequency in patients with PNH and the fact that they met four screening conditions, was determined in these CD59^- cells. Cell proliferation, apoptosis and cell cycle were evaluated upon knocking down the recombinant signal binding protein of immunoglobulin κJ region (RBPJ) gene in 5 patients in vitro. The detection rate of PIG-A gene mutation was 61.54% (8/13), and additional mutations in somatic genes were detected, including RBPJ, zinc finger protein 717, polycomb repressive complex 2 subunit and tet methylcytosine dioxygenase. Upon screening according to the mutation frequency and expression level, the present study focused on the RBPJ gene. The expression level of RBPJ in CD59^- cells was apparently higher than that in CD59⁺ cells and normal controls which was significantly correlated with clinical data. Furthermore, the expression of RBPJ in PNH primary cells could be effectively inhibited by small interfering RNA-RBPJ. Once the expression of RBPJ decreased remarkably, the apoptotic rate increased gradually, while cell proliferation activity decreased with transfection time and cells were blocked in G0/G1 phase. In conclusion, mutations and abnormal expression of the RBPJ gene may participate in the abnormal proliferation of PNH clones.

Clonal approaches to understanding the impact of mutations on hematologic disease development

Interrogation of hematopoietic tissue at the clonal level has a rich history spanning over 50 years, and has provided critical insights into both normal and malignant hematopoiesis. Characterization of chromosomes identified some of the first genetic links to cancer with the discovery of chromosomal translocations in association with many hematological neoplasms. The unique accessibility of hematopoietic tissue and the ability to clonally expand hematopoietic progenitors in vitro has provided fundamental insights into the cellular hierarchy of normal hematopoiesis, as well as the functional impact of driver mutations in disease. Transplantation assays in murine models have enabled cellular assessment of the functional consequences of somatic mutations in vivo. Most recently, next-generation sequencing-based assays have shown great promise in allowing multi-"omic" characterization of single cells. Here, we review how clonal approaches have advanced our understanding of disease development, focusing on the acquisition of somatic mutations, clonal selection, driver mutation cooperation, and tumor evolution.

Iron Deficiency in Patients with Paroxysmal Nocturnal Hemoglobinuria: A Cross-Sectional Survey from a Single Institution in China

Background

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal hematopoietic disorder that often manifests with chronic intravascular hemolysis. Iron deficiency in patients with PNH is most often due to urinary losses of iron secondary to chronic intravascular hemolysis.

Material/Methods

This cross-sectional survey assessed the prevalence of iron deficiency in a Chinese population of PNH patients who were enrolled between May 2012 and October 2014.

Results

A total of 742 PNH cases were selected by FLARE and classified as classical PNH (15.36%), PNH in the setting of another specified bone marrow disorder (12.26%), and subclinical PNH (72.38%). The median age of all the patients was 32 years (range 5–77 years). The overall prevalence of iron deficiency was 17.9% among all the PNH patients enrolled in the survey, 76.3% (87/144) among those with classical PNH, 33.0% (30/91) among those with PNH in the setting of another specified bone marrow disorder, and 3.0% (16/537) among the subclinical PNH patients. The incidence of iron deficiency among classical PNH patients was higher than that in the other 2 subcategories (P-value=0.000). Multivariate analyses showed that age and disease duration were independent risk factors for iron deficiency in classical patients.

Conclusions

This survey shows that PNH patients were prone to iron deficiency, especially patients with classical PNH.

Molecular Pathology: Prognostic and Diagnostic Genomic Markers for Myeloid Neoplasms

Application of next-generation sequencing (NGS) on myeloid neoplasms has expanded our knowledge of genomic alterations in this group of diseases. Genomic alterations in myeloid neoplasms are complex, heterogeneous, and not specific to a disease entity. NGS-based panel testing of myeloid neoplasms can complement existing diagnostic modalities and is gaining acceptance in the clinics and diagnostic laboratories. Prospective, randomized trials to evaluate the prognostic significance of genomic markers in myeloid neoplasms are under way in academic medical centers.

Development of paroxysmal nocturnal hemoglobinuria in CALR-positive myeloproliferative neoplasm

Paroxysmal nocturnal hemoglobinuria (PNH), a disease characterized by intravascular hemolysis, thrombosis, and bone marrow failure, is associated with mutations in the PIG-A gene, resulting in a deficiency of glycosylphosphatidylinositol-anchored proteins. Many hypotheses have been posed as to whether PNH and PIG-A mutations result in an intrinsic survival benefit of CD55(-)/CD59(-) cells or an extrinsic permissive environment that allows for their clonal expansion within the bone marrow compartment. Recent data have identified the concurrence of PIG-A mutations with additional genetic mutations associated with myeloproliferative disorders, suggesting that some presentations of PNH are the result of a stepwise progression of genetic mutations similar to other myelodysplastic or myeloproliferative syndromes. We report for the first time in the literature the development of clinically significant PNH in a patient with JAK2V617F-negative, CALR-positive essential thrombocythemia, providing further support to the hypothesis that the development of PNH is associated with the accumulation of multiple genetic mutations that create an intrinsic survival benefit for clonal expansion. This case study additionally highlights the utility of genomic testing in diagnosis and the understanding of disease progression in the clinical setting.

Minor populations of paroxysmal nocturnal hemoglobinuria-type cells in patients with chronic idiopathic neutropenia

Chronic idiopathic neutropenia (CIN) is an acquired disorder of granulopoiesis characterized by increased apoptosis of the bone marrow (BM) granulocytic progenitor cells under the influence of pro-inflammatory mediators and oligoclonal/monoclonal T-lymphocytes. Because patients with immune-mediated BM failure display frequently paroxysmal nocturnal hemoglobinuria (PNH)-type cells in the peripheral blood (PB), we investigated the possible existence of PNH-type cells in 91 patients with CIN using flow cytometry. The patients displayed increased proportions of PNH-type glycophorin A⁺ /CD59^dim and glycophorin A⁺ /CD59^- red blood cells (RBCs), FLAER^- /CD24^- granulocytes, and FLAER^- /CD14^- monocytes, compared to controls (n = 55). A positive correlation was found between the proportions of PNH-type RBCs, granulocytes, and monocytes and an inverse correlation between the number of PB neutrophils and the proportions of PNH-type cell populations. The number of patients, displaying percentages of PNH-type cells above the highest percentage observed in the control group, was significantly increased among patients with skewed compared to those with normal T-cell receptor repertoire suggesting that T-cell-mediated immune processes underlie the emergence of PNH-type cells in CIN. Our findings suggest that patients with CIN display PNH-type cells in the PB at a high frequency corroborating the hypothesis that CIN belongs to the immune-mediated BM failure syndromes.

Current international flow cytometric practices for the detection and monitoring of paroxysmal nocturnal haemoglobinuria clones: A UK NEQAS survey

BACKGROUND

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare acquired genetic disorder, with an incidence of approximately 1.3 new cases per million population per year. Evidence from the UK National External Quality Assessment Service for Leucocyte Immunophenotyping (UK NEQAS LI) programme suggested major discrepancies on how PNH testing is undertaken. To investigate this we surveyed laboratories in the UK NEQAS LI PNH programme and report here the findings.

METHODS

A questionnaire was distributed to all centres registered in UK NEQAS LI flow cytometry programmes (n = 1587). Comprising several subsections, it covered the majority of clinical flow cytometric practices. Participants completed a general section and then the subsections relevant to their laboratory repertoire. One subsection contained 34 questions regarding practices in PNH clone detection.

RESULTS

A total of 105 laboratories returned results for the PNH section; the results demonstrated lack of consensus in all areas of PNH testing. Variation was seen in gating and testing strategies, sensitivity levels and final reporting of test results. Several incorrect practices were highlighted such as inappropriate antibody selection and failure to wash the red blood cells (RBCs) prior to analysis.

CONCLUSION

Despite the availability of consensus guidelines there appears to be no agreement in the detection and monitoring of PNH. We found only fourteen centres using methods compatible with the International Clinical Cytometry Society guidelines. Of specific note we found that no two laboratories used the same method. This technical variation could lead to incorrect diagnoses, highlighting the need for better adoption and understanding of consensus practices. © 2016 International Clinical Cytometry Society.

[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.

The epidemiology of venous thromboembolism

Venous thromboembolism (VTE) is categorized by the U.S. Surgeon General as a major public health problem. VTE is relatively common and associated with reduced survival and substantial health-care costs, and recurs frequently. VTE is a complex (multifactorial) disease, involving interactions between acquired or inherited predispositions to thrombosis and VTE risk factors, including increasing patient age and obesity, hospitalization for surgery or acute illness, nursing-home confinement, active cancer, trauma or fracture, immobility or leg paresis, superficial vein thrombosis, and, in women, pregnancy and puerperium, oral contraception, and hormone therapy. Although independent VTE risk factors and predictors of VTE recurrence have been identified, and effective primary and secondary prophylaxis is available, the occurrence of VTE seems to be relatively constant, or even increasing.

Distinct subgroups of paroxysmal nocturnal hemoglobinuria (PNH) with cytopenia: results from South Korean National PNH Registry

We retrospectively assessed the clinical characteristics of patients with paroxysmal nocturnal hemoglobinuria (PNH) according to severity of cytopenia. A total of 282 patients with hematological parameters assessed at the time of diagnosis of PNH were included. There were 24 patients with PNH/severe aplastic anemia (SAA) (at least two of the three criteria; hemoglobin ≤8 g/dL; absolute neutrophil count (ANC) <0.5 × 10(9)/L; platelet count <20 × 10(9)/L), 96 patients with PNH/aplastic anemia (AA) (at least two of the three criteria; hemoglobin ≤10 g/dL; ANC 0.5-1.5 × 10(9)/L; platelet count 20-100 × 10(9)/L), and 162 classic PNH patients. Compared with the classic PNH subgroup, the PNH/SAA subgroup had a significantly lower median granulocyte PNH clone size (26.7 vs. 51.0 %, P = 0.021) and lower incidence of lactate dehydrogenase ≥1.5 times the upper limit of normal (52.9 vs. 80.0 %, P = 0.049). The incidence of thromboembolism was similar in both subgroups. Overall survival was significantly lower in the PNH/SAA subgroup than in the classic PNH subgroup (P = 0.033). Our findings suggest that identification of patients with PNH/SAA at the time of diagnosis is important because of different clinical manifestations and poorer outcome compared with patients with classic PNH (clinicaltrials.gov identifier: #NCT01224483).

[Paroxysmal nocturnal hemoglobinuria: An unknown cause of thrombosis?]

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired disorder of hematopoietic stem cells. Somatic mutation in the phosphatidylinositol glycan class A (PIG-A), X-linked gene, is responsible for a deficiency in glycosphosphatidylinositol-anchored proteins (GPI-AP). The lack of one of the GPI-AP complement regulatory proteins (CD55, CD59) leads to hemolysis. The disease is diagnosed with hemolytic anemia, marrow failure and thrombosis. Thromboembolic complication occurs in 30% of patient after 10 years of follow-up and is the first event in one out of 10 patients. The two most common sites are hepatic and cerebral veins. These locations are correlated with high risk of death. Currently, these data are balanced with the use of a monoclonal antibody (Eculizumab), which has significantly improved the prognosis with a survival similar to general population after 36 months of follow-up. Anticoagulant treatment is recommended after a thromboembolic event but has no place in primary prophylaxis.

Epidemiology of venous thromboembolism

Thrombosis can affect any venous circulation. Venous thromboembolism (VTE) includes deep-vein thrombosis of the leg or pelvis, and its complication, pulmonary embolism. VTE is a fairly common disease, particularly in older age, and is associated with reduced survival, substantial health-care costs, and a high rate of recurrence. VTE is a complex (multifactorial) disease, involving interactions between acquired or inherited predispositions to thrombosis and various risk factors. Major risk factors for incident VTE include hospitalization for surgery or acute illness, active cancer, neurological disease with leg paresis, nursing-home confinement, trauma or fracture, superficial vein thrombosis, and-in women-pregnancy and puerperium, oral contraception, and hormone therapy. Although independent risk factors for incident VTE and predictors of VTE recurrence have been identified, and effective primary and secondary prophylaxis is available, the occurrence of VTE seems to be fairly constant, or even increasing.

Paroxysmal nocturnal hemoglobinuria clone in 103 Brazilian patients: diagnosis and classification

BACKGROUND

Paroxysmal nocturnal hemoglobinuria is an acquired chronic hemolytic anemia, which often manifests as peripheral blood cytopenias and thrombosis.

OBJECTIVE

The aim of this study is to describe a Brazilian population of paroxysmal nocturnal hemoglobinuria patients.

METHODS

One hundred and three paroxysmal nocturnal hemoglobinuria cases were retrospectively reviewed and the clinical presentation, thrombosis, survival, and clone size were assessed. Diagnosis was established by flow cytometry.

RESULTS

Fifty-two male and 51 female patients with a median age of 24.1 years (5.5-62 years) were studied. Clinical symptoms included hemoglobinuria (18.4%), infection (46.6%) and thrombosis (16.5%), and 80.6% had pancytopenia. Patients were classified as classic paroxysmal nocturnal hemoglobinuria (10), paroxysmal nocturnal hemoglobinuria with aplastic anemia (39), and paroxysmal nocturnal hemoglobinuria with subclinical features and aplastic anemia (54). There were significant differences in terms of median age, size of clone, clinical symptoms, and peripheral blood cell counts between the three subcategories. The clone size in erythrocytes and granulocytes were respectively 0.04% (range: 0-18%) and 7.3% (range: 0.3-68.7%) in patients with subclinical features and aplastic anemia, 15.8% (range: 0-99.7%) and 63.0% (range: 1.7-99.8%) in patients with aplastic anemia alone, and 82.2% (range: 0-99.85%) and 98.0% (81.3-100.0%) in Classic disease. Statistical differences were identified for platelets (p-value=0.001), lactate dehydrogenase (p-value=0.002) and the clone size (p-value<0.001) in patients who suffered thrombotic events compared to those who did not. Overall survival was 81.7%, with patients with subclinical features and aplastic anemia having lower overall survival (76.5%).

CONCLUSION

This retrospective review of 103 patients over an 11-year period represents the largest collection of paroxysmal nocturnal hemoglobinuria cases from a single center in Brazil. Flow cytometry showed that a larger clone was associated with classical symptoms and increased risk of thrombosis, even in patients with bone marrow failure, whereas a smaller clone was associated with bone marrow aplasia.

Deep sequencing reveals stepwise mutation acquisition in paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a nonmalignant clonal disease of hematopoietic stem cells that is associated with hemolysis, marrow failure, and thrombophilia. PNH has been considered a monogenic disease that results from somatic mutations in the gene encoding PIGA, which is required for biosynthesis of glycosylphosphatidylinisotol-anchored (GPI-anchored) proteins. The loss of certain GPI-anchored proteins is hypothesized to provide the mutant clone with an extrinsic growth advantage, but some features of PNH argue that there are intrinsic drivers of clonal expansion. Here, we performed whole-exome sequencing of paired PNH+ and PNH- fractions on samples taken from 12 patients as well as targeted deep sequencing of an additional 36 PNH patients. We identified additional somatic mutations that resulted in a complex hierarchical clonal architecture, similar to that observed in myeloid neoplasms. In addition to mutations in PIGA, mutations were found in genes known to be involved in myeloid neoplasm pathogenesis, including TET2, SUZ12, U2AF1, and JAK2. Clonal analysis indicated that these additional mutations arose either as a subclone within the PIGA-mutant population, or prior to PIGA mutation. Together, our data indicate that in addition to PIGA mutations, accessory genetic events are frequent in PNH, suggesting a stepwise clonal evolution derived from a singular stem cell clone.

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).

Response of paroxysmal nocturnal hemoglobinuria clone with aplastic anemia to rituximab

Paroxysmal nocturnal hemoglobinuria is caused by expansion of a hematopoietic stem cell clone with an acquired somatic mutation in the PIG-A gene. This mutation aborts the synthesis and expression of the glycosylphosphatidylinositol anchor proteins CD55 and CD59 on the surface of blood cells, thereby making them more susceptible to complement-mediated damage. A spectrum of disorders occurs in PNH ranging from hemolytic anemia and thrombosis to myelodysplasia, aplastic anemia and, myeloid leukemias. Aplastic anemia is one of the most serious and life-threatening complications of PNH, and a PNH clone is found in almost a third of the cases of aplastic anemia. While allogeneic bone marrow transplantation and T cell immune suppression are effective treatments for aplastic anemia in PNH, these therapies have significant limitations. We report here the first case, to our knowledge, of PNH associated with aplastic anemia treated with the anti-CD20 monoclonal antibody rituximab, which was associated with a significant reduction in the size of the PNH clone and recovery of hematopoiesis. We suggest that this less toxic therapy may have a significant role to play in treatment of PNH associated with aplastic anemia.

Ex vivo expansion and long-term hematopoietic reconstitution ability of sorted CD34+CD59+ cells from patients with paroxysmal nocturnal hemoglobinuria

Autologous bone marrow transplantation (ABMT) for paroxysmal nocturnal hemoglobinuria (PNH) remains difficult so far. To expand residual normal CD34(+)CD59(+) cells isolated from patients with PNH and observe the long-term hematopoietic reconstruction ability of the expanded cells both ex vivo and in vivo, CD34(+)CD59(+) cells from 13 PNH patients and CD34(+) cells from 11 normal controls were separated from bone marrow mononuclear cells first by immunomagnetic microbeads and then by flow cytometry autoclone sorting. The cells were then cultivated under different conditions. The long-term hematopoietic supporting ability of expanded CD34(+)CD59(+) cells was evaluated by long-term culture in semi-solid medium in vitro and long-term engraftment in irradiated severe combined immunodeficiency (SCID) mice in vivo. The best combination of hematopoietic growth factors for ex vivo expansion was SCF + IL-3 + IL-6 + FL + Tpo + Epo. The most suitable time for harvest was on day 7. CD34(+)CD59(+) PNH cells retained strong colony-forming capacity even after expansion. The survival rate, complete blood cell count recovery on day 90, and human CD45 expression in different organs were similar between the irradiated SCID mice transplanted with expanded CD34(+)CD59(+) PNH cells and those with normal CD34(+) cells (P > 0.05) both in primary and secondary transplantation. These data provided a new potential way of managing PNH with ABMT.

Acquired thrombotic risk factors in the critical care setting

Acquired thrombotic risk factors include a variety of noninherited clinical conditions that can predispose an individual to an increased risk for venous thromboembolism. For patients in a critical care setting, certain acquired risk factors represent chronic conditions that the patients may have had before the current acute illness (e.g., malignancy, various cardiovascular risk factors, certain medications), whereas others may be directly related to the reason the patient is in an intensive care unit or the patient's management there (e.g., postoperative state, trauma, indwelling vascular access, certain medications). Optimal thromboprophylactic strategies depend on individual patient risk profiles including an assessment of the specific clinical setting. Treatment for patients with acquired thrombotic risk factors includes anticoagulant therapy and, if possible, resolution of the acquired risk factor(s). Heparin-induced thrombocytopenia represents a unique clinical situation in which all sources of heparin must be discontinued and the patient started on an alternative anticoagulant (e.g., a direct thrombin inhibitor) in the acute setting. The duration of anticoagulant therapy would vary depending on the specific clinical setting.

The pathophysiology of disease in patients with paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired hemolytic anemia caused by the expansion of a hematopoietic progenitor cell that has acquired a mutation in the X-linked PIGA gene. PNH occurs on the background of bone marrow failure. Bone marrow failure and the presence of the abnormal cells account for the clinical phenotype of patients with PNH including hemolysis, cytopenia, and thrombophilia. PIGA is essential for the synthesis of glycosyl phosphatidylinositol (GPI) anchor molecules. PNH blood cells are therefore deficient in all proteins that use such an anchor molecule for attachment to the cell membrane. Two of these proteins regulate complement activation on the cell surface. Their deficiency therefore explains the exquisite sensitivity of PNH red blood cells to complement-mediated lysis. Complement-mediated lysis of red blood cells is intravascular, and intravascular hemolysis contributes significantly to the morbidity and mortality in patients with this condition. PNH is an outstanding example of how an increased understanding of pathophysiology may directly improve the diagnosis, care, and treatment of disease.