Clinical characteristics predict response to antithymocyte globulin in paroxysmal nocturnal haemoglobinuria

Paroxysmal Nocturnal Hemoglobinuria: Biology and Treatment

Paroxysmal nocturnal hemoglobinuria (PNH) is a nonmalignant clonal hematopoietic disorder characterized by the lack of glycosylphosphatidylinositol-anchored proteins (GPI-APs) as a consequence of somatic mutations in the phosphatidylinositol glycan anchor biosynthesis class A (PIGA) gene. Clinical manifestations of PNH are intravascular hemolysis, thrombophilia, and bone marrow failure. Treatment of PNH mainly relies on the use of complement-targeted therapy (C5 inhibitors), with the newest agents being explored against other factors involved in the complement cascade to alleviate unresolved intravascular hemolysis and extravascular hemolysis. This review summarizes the biology and current treatment strategies for PNH with the aim of reaching a general audience with an interest in hematologic disorders.

Inhibition of C3 with pegcetacoplan results in normalization of hemolysis markers in paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, acquired hematologic disorder characterized by complement-mediated hemolysis. C5 inhibitors (eculizumab/ravulizumab) control intravascular hemolysis but do not prevent residual extravascular hemolysis. The newly approved complement inhibitor, pegcetacoplan, inhibits C3, upstream of C5, and has the potential to improve control of complement-mediated hemolysis. The PADDOCK and PALOMINO clinical trials assessed the safety and efficacy of pegcetacoplan in complement inhibitor-naïve adults (≥ 18 years) diagnosed with PNH. Patients in PADDOCK (phase 1b open-label, pilot trial) received daily subcutaneous pegcetacoplan (cohort 1: 180 mg up to day 28 [n = 3]; cohort 2: 270–360 mg up to day 365 [n = 20]). PALOMINO (phase 2a, open-label trial) used the same dosing protocol as PADDOCK cohort 2 (n = 4). Primary endpoints in both trials were mean change from baseline in hemoglobin, lactate dehydrogenase, haptoglobin, and the number and severity of treatment-emergent adverse events. Mean baseline hemoglobin levels were below the lower limit of normal in both trials (PADDOCK: 8.38 g/dL; PALOMINO: 7.73 g/dL; normal range: 11.90–18.00 g/dL), increased to within normal range by day 85, and were sustained through day 365 (PADDOCK: 12.14 g/dL; PALOMINO: 13.00 g/dL). In PADDOCK, 3 serious adverse events (SAE) led to study drug discontinuation, 1 of which was deemed likely related to pegcetacoplan and 1 SAE, not deemed related to study drug, led to death. No SAE led to discontinuation/death in PALOMINO. Pegcetacoplan was generally well tolerated and improved hematological parameters by controlling hemolysis, while also improving other clinical PNH indicators in both trials. These trials were registered at www.clinicaltrials.gov (NCT02588833 and NCT03593200).

The Role of T Lymphocytes in the Pathogenesis of Paroxysmal Nocturnal Hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired hematopoietic stem cell genetic mutation disease that causes defective erythrocyte membrane hemolysis. Its pathologic basis is the mutation of the PIG-A gene, whose product is necessary for the synthesis of glycosylphosphatidylinositol (GPI) anchors; the mutation of PIG-A gene results in the reduction or deletion of the GPI anchor, which leads to the deficiency of GPI-anchored proteins (GPI-APs), such as CD55 and CD59, which are complement inhibitors. The deficiency of complement inhibitors causes chronic complement-mediated intravascular hemolysis of GPI-anchor-deficient erythrocyte. PIG-A gene mutation could also be found in bone marrow hematopoietic stem cells (HSCs) of healthy people, but they have no growth advantage; only the HSCs with PIG-A gene mutation in PNH patients have this advantage and expand. Besides, HSCs from PIG-A-knockout mice do not show clonal expansion in bone marrow, so PIG-A mutation cannot explain the clonal advantage of the PNH clone and some additional factors are needed; thus, in recent years, many scholars have put forward the theories of the second hit, and immune escape theory is one of them. In this paper, we focus on how T lymphocytes are involved in immune escape hypothesis in the pathogenesis of PNH.

Eculizumab for treating patients with paroxysmal nocturnal hemoglobinuria

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is a chronic, not malignant, disease of the hematopoietic stem cells, associated with significant morbidity and mortality. It is a rare disease with an estimated incidence of 1.3 new cases per one million individuals per year. The treatment of PNH has been largely empirical and symptomatic, with blood transfusions, anticoagulation, and supplementation with folic acid or iron. Eculizumab, a biological agent that inhibits complement cascade, was developed for preventing hemolytic anemia and severe thrombotic episodes.

OBJECTIVES

To assess the clinical benefits and harms of eculizumab for treating patients with paroxysmal nocturnal hemoglobinuria (PNH).

SEARCH METHODS

We conducted a comprehensive search strategy. We searched the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library 2014, Issue 5), Ovid MEDLINE (from 1946 to 15 May 2014), EMBASE (from 1980 to 25 June 2014), and LILACS (from 1982 to 25 June 2014). We did not apply any language restrictions.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) irrespective of their publication status or language. No limits were applied with respect to period of follow-up. We excluded quasi-RCTs. We included trials comparing eculizumab with placebo or best available therapy. We included any patient with a confirmed diagnosis of PNH. Primary outcome was overall survival.

DATA COLLECTION AND ANALYSIS

We independently performed a duplicate selection of eligible trials, risk of bias assessment, and data extraction. We estimated risk ratios (RRs) and 95% confidence interval (CIs) for dichotomous outcomes, and mean differences (MDs) and 95% CIs for continuous outcomes. We used a random-effects model for analysis.

MAIN RESULTS

We identified one multicenter (34 sites) phase III RCT involving 87 participants. The trial compared eculizumab versus placebo, and was conducted in the US, Canada, Europe, and Australia with 26 weeks of follow-up. This small trial had high risk of bias in many domains (attrition and selective reporting). It was sponsored by a pharmaceutical company. No patients died during the study. By using the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (scores can range from 0 to 100, with higher scores on the global health status and functioning scales indicating improvement), the trial showed improvement in health-related quality of life in patients treated with eculizumab (mean difference (MD) 19.4, 95% CI 8.25 to 30.55; P = 0.0007; low quality of evidence). By using the Functional Assessment of Chronic Illness Therapy Fatigue instrument (scores can range from 0 to 52, with higher scores indicating improvement in fatigue), the trial showed a reduction in fatigue (MD 10.4, 95% CI 9.97 to 10.83; P = 0.00001; moderate quality of evidence) in the eculizumab group compared with placebo. Eculizumab compared with placebo showed a greater proportion of patients with transfusion independence: 51% (22/43) versus 0% (0/44); risk ratio (RR) 46.02, 95% CI 2.88 to 735.53; P = 0.007; moderate quality of evidence; and withdrawal for any reason: 4.7% (2/43) versus 22.72% (10/44); RR 0.20, 95% CI 0.05 to 0.88; P = 0.03; moderate quality of evidence. Due to the low rate of events observed, the included trial did not show any difference between eculizumab and placebo in terms of serious adverse events: 9.3% (4/43) versus 20.4% (9/44); RR 0.15, 95% CI 0.15 to 1.37; P = 0.16; low quality of evidence. We did not observe any difference between intervention and placebo for the most frequent adverse events. One participant receiving placebo showed an episode of thrombosis. The trial did not assess overall survival, transformation to myelodysplastic syndrome and acute myelogenous leukemia, or development or recurrence of aplastic anemia on treatment.

AUTHORS' CONCLUSIONS

This review has detected an absence of evidence for eculizumab compared with placebo for treating paroxysmal nocturnal hemoglobinuria (PNH), in terms of overall survival, nonfatal thrombotic events, transformation to myelodysplastic syndrome and acute myelogenous leukemia, and development and recurrence of aplastic anemia on treatment. Current evidence indicates that compared with placebo, eculizumab increases health-related quality of life and increases transfusion independence. During the execution of the included trial, no patients died. Furthermore, the intervention seems to reduce fatigue and withdrawals for any reason. The safety profile of eculizumab is unclear. These conclusions are based on one small trial with risk of attrition and selective reporting bias.Therefore, prescription of eculizumab for treating patients with PNH can neither be supported nor rejected, unless new evidence from a large high quality trial alters this conclusion. Therefore, we urge the reader to interpret the trial results with much caution. Future trials on this issue should be conducted according to the SPIRIT statement and reported according to the CONSORT statement by independent investigators, and using the Foundation of Patient-Centered Outcomes Research recommendations.

Paroxysmal nocturnal hemoglobinuria: rare cause of acute renal failure

Paroxysmal nocturnal hemoglobinuria is a rare acquired disease, characterized by hemolytic anemia, recurrent infections, cytopenias, and vascular thrombosis. It occurs by non-malignant clonal expansion of one or more hematopoietic stem cells that acquired somatic mutations in PIG-A gene linked to chromosome X. This mutation results in lower erythrocyte expression of CD55 and CD59 surface proteins and consequently increased susceptibility to the complement system. The renal involvement is generally benign, resulting in mild impairment in urinary concentration. Acute renal failure requiring hemodialytic support accompanying PNH is rarely observed. The authors report a case of a 37-year-old male who presented with bicytopenia (hemolytic anemia and thrombocytopenia) associated with acute renal failure requiring dialysis. Diagnosis was challenging because of the rarity and unfamiliarity with this entity, but was confirmed by flow cytometry. In the course of the disease, acute pyelonephritis with multiple renal abscesses was diagnosed requiring prolonged antibiotic therapy. Patient outcome was favorable after the control of hemolysis and the infection treatment.

Clonal Evolution in Aplastic Anemia

Current immunosuppressive treatment (IST) induces remissions in 50%-70% of patients with aplastic anemia (AA) and result in excellent long-term survival. In recent years, the survival of refractory patients has also improved. Apart from relapse and refractoriness to IST, evolution of clonal diseases, including paroxysmal nocturnal hemoglobinuria and myelodysplastic syndrome (MDS), are the most serious long-term complications and constitute a strong argument for definitive therapy with BM transplantation if possible. Consequently, the detection of diagnostic chromosomal abnormalities (mostly monosomy 7) is of great clinical importance. Newer whole-genome scanning technologies such as single nucleotide polymorphism (SNP) array–based karyotyping may be a helpful diagnostic test for the detection of chromosomal defects in AA due to its precision/resolution and lack of reliance on cell division.

Epidemiology of rare anaemias in Europe

Registry and epidemiological data of Rare Anaemias (RA) in Europe is in general still incomplete and/or partially documented. One important issue is the increasing prevalence of haemoglobin disorders (HD) due to migrations from high prevalence areas. The size of the problem, particularly for sickle cell disease (SCD), is already having an impact on health services in many European countries. The best known cause of rare anaemias associated with congenital haemolytic anaemia (CHA) in Europe is Hereditary Spherocytosis (HS) a red blood cell (RBC) membrane defect with a prevalence of 1 to 5 cases per 10.000 individuals. Some other causes of CHA are extremely rare and only few individual cases have been described worldwide (i.e. some RBC enzymopathies). Congenital defects of erythropoiesis are less frequent Diamond-Blackfan Anaemia (DBA) and Fanconi Anaemia (FA) exhibit a very low prevalence ranging from 4 to 7 per million live births. Congenital Dyserythropoietic Anaemia (CDA), a genetically heterogenous group, is still less frequent and exhibits a large variability of frequency depending on the European region: 0.1-3.0 cases per million births In addition many cases are known from a large autosomal dominant family in Sweden. Although incidence of Paroxysmal Nocturnal Haemoglobinuria (PNH) in Europe is still unknown, data collection from different sources has given quotes of 1 case per 100,000 individuals to 5 cases per million births.

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.

Effect of eculizumab on haemolysis-associated nitric oxide depletion, dyspnoea, and measures of pulmonary hypertension in patients with paroxysmal nocturnal haemoglobinuria

Pulmonary hypertension (PH) is a common complication of haemolytic anaemia. Intravascular haemolysis leads to nitric oxide (NO) depletion, endothelial and smooth muscle dysregulation, and vasculopathy, characterized by progressive hypertension. PH has been reported in patients with paroxysmal nocturnal haemoglobinuria (PNH), a life-threatening haemolytic disease. We explored the relationship between haemolysis, systemic NO, arginine catabolism and measures of PH in 73 PNH patients enrolled in the placebo-controlled TRIUMPH (Transfusion Reduction Efficacy and Safety Clinical Investigation Using Eculizumab in Paroxysmal Nocturnal Haemoglobinuria) study. At baseline, intravascular haemolysis was associated with elevated NO consumption (P < 0.0001) and arginase-1 release (P < 0.0001). Almost half of the patients in the trial had elevated levels (> or =160 pg/ml) of N-terminal pro-brain natriuretic peptide (NT-proBNP), a marker of pulmonary vascular resistance and right ventricular dysfunction previously shown to indicate PH. Eculizumab treatment significantly reduced haemolysis (P < 0.001), NO depletion (P < 0.001), vasomotor tone (P < 0.05), dyspnoea (P = 0.006) and resulted in a 50% reduction in the proportion of patients with elevated NT-proBNP (P < 0.001) within 2 weeks of treatment. Importantly, the significant improvements in dyspnoea and NT-proBNP levels occurred without significant changes in anaemia. These data demonstrated that intravascular haemolysis in PNH produces a state of NO catabolism leading to signs of PH, including elevated NT pro-BNP and dyspnoea that are significantly improved by treatment with eculizumab.

Neutral evolution in paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria is an acquired hematopoietic stem cell (HSC) disorder characterized by the partial or complete deficiency of glycosyl-phosphatidylinositol (GPI)-linked membrane proteins, which leads to intravascular hemolysis. A loss of function mutation in the PIG-A gene, required for GPI biosynthesis, explains how the deficiency of many membrane proteins can result from a single genetic event. However, to date the mechanism of expansion of the GPI(-) clone has not been fully understood. Two hypotheses have been proposed: A selective advantage of GPI(-) cells because of a second mutation or a conditional growth advantage of GPI(-) cells in the presence of an immune attack on normal (GPI(+)) HSCs. Here, we explore a third possibility, whereby the PNH clone does not have a selective advantage. Simulations in a large virtual population accurately reproduce the known incidence of the disease; and the fit is optimized when the number of stem cells is decreased, reflecting a component of bone marrow failure in PNH. The model also accounts for the occurrence of spontaneous cure in PNH, consequent on clonal extinction. Thus, a clonal advantage may not be always necessary to explain clonal expansion in PNH.

Paroxysmal nocturnal hemoglobinuria in childhood and adolescence--a retrospective analysis of 18 cases

OBJECTIVE

To assess the clinical and hematological profile of PNH in children.

METHODS

Clinical and laboratory features of children with PNH diagnosed in the past six years at our centre were reviewed. Various investigations done included a complete blood count and peripheral smear examination, plasma hemoglobin, urine hemosiderin, acid ham test, sucrose lysis test, immunophenotyping of erythrocytes by sephadex column gel card and of granulocytes by flow cytometry. There were 18 children with a marked male predominance (M 14: F 4).

RESULTS

Pallor, jaundice, dark urine and bleeding manifestations were the major presenting complaints. One girl suffered an arterial stroke. All children had cytopenia in at least one cell line. Children were treated with danazol, stanazolol, prednisolone and cyclosporin A variously. Overall response rate was 61%. Children with classical PNH performed slightly better with response rates of 66% (6/9) as compared to aplastic anemia-PNH group which has a response rate of 55% (5/9). Amongst various variables only danazol correlated with better response (p=0.029).

CONCLUSION

PNH is an uncommon disease in children and should be included in the differential diagnosis of children presenting with cytopenia.

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.

Apparent hemolysis following intravenous antithymocyte globulin treatment in a patient with marrow failure and a paroxysmal nocturnal hemoglobinuria clone

BACKGROUND

Antithymocyte globulin (ATG) is a commonly used medication in the treatment of aplastic anemia. Although serum sickness has been described with the use of ATG, few cases of acute intravascular hemolysis have been reported. We report a case of apparent ATG-related hemolysis in a patient with aplastic anemia and a paroxysmal nocturnal hemoglobinuria (PNH) clone.

CASE REPORT

A 62-year-old, group A, RhoD+ man with aplastic anemia and an 11.6 percent glycosylphosphatidylinositol (GPI)-anchored protein-negative population of red cells (RBCs), representing approximately 190 mL of his RBC volume, and 90 percent GPI-negative neutrophils were scheduled to receive equine ATG at 40 mg per kg per day for 4 days. After the first infusion, he developed a 1.6 g per dL decline in hemoglobin concentration and an increase in serum lactate dehydrogenase (normal, 113-226 U/L) from 284 to 1127 U per L. The hemolytic process was complicated by acute renal failure characterized by an increase in serum creatinine from 0.9 to 4.2 mg per dL and the appearance of dark-colored urine. Pre- and post-ATG direct antiglobulin tests were negative.

CONCLUSION

The temporal association of intravenous ATG to lysis of complement-sensitive RBCs suggests a causal relationship. Although intravascular hemolysis after ATG administration appears to be uncommon, the clinical consequences may be severe, and determining the pathophysiology may yield clues to the mechanism of intravascular hemolysis.

Sustained response and long-term safety of eculizumab in paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a hematologic disorder characterized by clonal expansion of red blood cells (RBCs) lacking the ability to inhibit complement-mediated hemolysis. Eculizumab, a humanized monoclonal antibody that binds the C5 complement protein, blocks serum hemolytic activity. This study evaluated the long-term safety and efficacy of eculizumab in 11 patients with PNH during an open-label extension trial. After completion of an initial 12-week study, all patients chose to participate in the 52-week extension study. Eculizumab, administered at 900 mg every 12 to 14 days, was sufficient to completely and consistently block complement activity in all patients. A dramatic reduction in hemolysis was maintained throughout the study, with a decrease in lactate dehydrogenase (LDH) levels from 3110.7 IU/L before treatment to 622.4 IU/L (P = .002). The proportion of PNH type III RBCs increased from 36.7% at baseline to 58.4% (P = .005). The paroxysm rate of days with gross evidence of hemoglobinuria per patient each month decreased from 3.0 during screening to 0.2 (P &lt; .001) during treatment. The median transfusion rate decreased from 1.8 U per patient each month before eculizumab treatment to 0.3 U per patient each month (P = .001) during treatment. Statistically significant improvements in quality-of-life measures were also maintained during the extension study. Eculizumab continued to be safe and well tolerated, and all patients completed the study. The close relationship between sustained terminal complement inhibition, hemolysis, and symptoms was demonstrated. (Blood. 2005; 106:2559-2565)

Clinical and molecular aspects of 23 patients affected by paroxysmal nocturnal hemoglobinuria

We reviewed clinical and molecular data of 23 consecutive unrelated patients affected by paroxysmal nocturnal hemoglobinuria (PNH) (19 with hemolytic PNH, 3 with aplastic anemia/PNH, and 1 with myelodysplasia/PNH syndrome) with a mean follow-up of 11.8 years. Five patients had thrombotic episodes, and 10 needed regular blood transfusions; 2 died for cerebral hemorrhage and kidney failure, and 2 spontaneously recovered from PNH. Twenty different PIG-A gene mutations were detected in 21/23 patients: 15 frameshift, 1 splicing, 2 nonsense, and 2 missense mutations. Two mutations (DelG341 and IVS2 +1g-a) were detected twice. A PIG-A mutated clone was also revealed in the two patients in complete clinical remission. One patient with aplastic anemia/PNH syndrome was treated with two courses of antilymphocyte globulin and cyclosporin with partial sustained response. Six patients were given rHu-EPO 150 U/kg/day s.c. for at least 6 months: one became transfusion-independent for 8 months and then discontinued treatment for clinical complications; one displayed a mean rise of Hb of 1.5 g/dL and is currently maintaining Hb levels higher than 9 g/dL after 54 months of therapy. Mutation specific quantitative-competitive PCR showed that the rise of hemoglobin was related to an increase of PIG-A negative molecules, suggesting that the efficacy of rHu-EPO therapy may be due to the stimulation of the abnormal clone.

Effect of proinflammatory cytokines on PIGA- hematopoiesis

OBJECTIVE

Blood cells from patients with paroxysmal nocturnal hemoglobinuria lack glycosyl phosphatidylinositol (GPI)-linked proteins, due to a somatic mutation in the X-linked PIGA gene. It is believed that clonal expansion of PIGA- blood cells is due to a survival advantage in the hostile marrow environment of aplastic anemia. Here we investigated the effects of inhibitory cytokines in mice genetically engineered to have blood cells deficient in GPI-linked proteins.

MATERIALS AND METHODS

The effect of inhibitory cytokines (tumor necrosis factor-alpha [TNF-alpha], interferon-gamma [IFN-gamma], macrophage inflammatory protein-1 alpha [MIP-1alpha], and transforming growth factor-beta1 [TGF-beta1]) was investigated, using clonogenic assays, competitive repopulation, and in vivo induction of proinflammatory cytokines by double-stranded RNA. The expression of Fas on progenitor cells and its up-regulation by inhibitory cytokines were analyzed by flow cytometry.

RESULTS

TNF-alpha, IFN-gamma, MIP-1alpha, and TGF-beta1 suppressed colony formation in a dose-dependent fashion that was similar for PIGA+ and PIGA- blood bone marrow cells. Competitive repopulation of bone marrow cells cultured in IFN-gamma and TNF-alpha resulted in a comparable ability of PIGA+ and PIGA- hematopoietic stem cells to reconstitute hematopoiesis. Fas expression was minimal on PIGA+ and PIGA- progenitor cells and was up-regulated to the same extent in response to IFN-gamma and TNF-alpha as assessed by Fas antibody-mediated apoptosis. Similarly, in vivo induction of proinflammatory cytokines by double-stranded RNA had no effect on the proportion of circulating PIGA- blood cells.

CONCLUSIONS

These results indicate that PIGA+ and PIGA- hematopoietic progenitor cells respond similarly to inhibitory cytokines, suggesting that other factors are responsible for the clonal expansion of paroxysmal nocturnal hemoglobinuria cells.

Anti-thymocyte globulin treatment of marrow aplasia associated with paroxysmal nocturnal haemoglobinuria (PNH) resulted in haematological improvement due to an expansion of the PNH clone

A patient with aplastic anaemia developed paroxysmal nocturnal haemoglobinuria (PNH) 4 years after diagnosis, with an ensuing haematopoietic improvement. The PNH clone subsequently declined, leading to pancytopenia again. Anti-thymocyte globulin had to be administered 14 years later, which resulted in haematopoietic improvement once more. Flow cytometric analysis showed that this was attributable to expansion of the PNH clone, owing probably to alleviation of its suppression by immune-mediated mechanisms. PIG-A gene analysis showed that the same PNH clone had waned and waxed in the clinical course. Our results suggest that the PNH clone might rarely be an immune target as well.

Dynamics of hematopoiesis in paroxysmal nocturnal hemoglobinuria (PNH): no evidence for intrinsic growth advantage of PNH clones

PNH is characterized by expansion of one or more stem cell clones with a PIG-A mutation, which causes a severe deficiency in the expression of glycosylphosphatidylinositol (GPI)-anchored proteins. There is evidence that the expansion of PIG-A mutant clones is concomitant with negative selection against PIG-A wild-type stem cells by an aplastic marrow environment. We studied 36 patients longitudinally by serial flow cytometry, and we determined the proportion of PNH red cells and granulocytes over a period of 1-6 years. We observed expansion of the PNH blood cell population(s) (at a rate of over 5% per year) in 12 out of 36 patients; in all other patients the PNH cell population either regressed or remained stable. The dynamics of the PNH cell population could not be predicted by clinical or hematologic parameters at presentation. These data indicate that in most cases the PNH cell expansion has already run its course by the time of diagnosis. In addition, since in most cases no further expansion takes place, we can infer that the tendency to overgrow normal cells is not an intrinsic property of the PNH clone.

Association of clonal T-cell large granular lymphocyte disease and paroxysmal nocturnal haemoglobinuria (PNH): further evidence for a pathogenetic link between T cells, aplastic anaemia and PNH

There is mounting evidence to suggest that T-cell-mediated suppression of haemopoiesis is a pathogenetic mechanism in three bone marrow failure syndromes: aplastic anaemia (AA), paroxysmal nocturnal haemoglobinuria (PNH) and myelodysplasia (MDS). T-cell microclones can be detected by sensitive polymerase chain reaction (PCR)-based methods in all three disorders. Recently, larger clonal populations of T-cell large granular lymphocytes (T-LGLs) have been observed in some patients with AA and MDS. Here, we report the development of a large clonal T-LGL population in a patient with bona fide PNH. In this patient, we defined part of the sequence of the T-cell receptor (TCR) beta-chain gene, and we have shown that the large T-LGL population emerged from a background of multiple smaller T-cell clones. Thus, T-LGL clones in AA, MDS and PNH probably expand as a result of antigenic stimulation. It is postulated that the antigen driving clonal T-cell proliferations in these disorders exists on haemopoietic stem cells.

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.

Lymphocyte Subset Analysis and Glycosylphosphatidylinositol Phenotype in Patients With Paroxysmal Nocturnal Hemoglobinuria

Using multicolor flow-cytometry we have examined 19 patients with paroxysmal nocturnal hemoglobinuria (PNH) (18 with active disease and 1 spontaneous remitter) to determine absolute numbers of lymphocyte subsets and the proportion of glycosylphosphatidylinositol (GPI)-deficient clones amongst these subpopulations. Lymphocyte subsets were abnormal in all patients; the most frequent findings were low absolute numbers of natural killer (NK) cells (median, 0.08 × 109/L; normal range, 0.2 to 0.4 × 109/L) and low absolute numbers of B cells (median, 0.05 × 109/L; normal range, 0.06 to 0.65 × 109/L). GPI-deficient B, T, and NK cells were identified in 88%, 84%, and 89% of patients, respectively. The proportion of GPI-deficient cells within individual lymphoid lineages was highly variable, though in most patients the percentage of GPI-deficient NK cells was considerably higher than B or T cells. These observations can be explained when mechanisms of normal lymphopoiesis are considered. Despite these quantitative and qualitative abnormalities, no patients suffered an excessive number or severity of infections. The detection of PNH clones amongst all lymphocyte lineages may provide important information regarding the natural history of the disease and additional insights into kinetics of adult lymphopoiesis.

© 1998 by The American Society of Hematology.

Lymphocyte Subset Analysis and Glycosylphosphatidylinositol Phenotype in Patients With Paroxysmal Nocturnal Hemoglobinuria

Using multicolor flow-cytometry we have examined 19 patients with paroxysmal nocturnal hemoglobinuria (PNH) (18 with active disease and 1 spontaneous remitter) to determine absolute numbers of lymphocyte subsets and the proportion of glycosylphosphatidylinositol (GPI)-deficient clones amongst these subpopulations. Lymphocyte subsets were abnormal in all patients; the most frequent findings were low absolute numbers of natural killer (NK) cells (median, 0.08 × 109/L; normal range, 0.2 to 0.4 × 109/L) and low absolute numbers of B cells (median, 0.05 × 109/L; normal range, 0.06 to 0.65 × 109/L). GPI-deficient B, T, and NK cells were identified in 88%, 84%, and 89% of patients, respectively. The proportion of GPI-deficient cells within individual lymphoid lineages was highly variable, though in most patients the percentage of GPI-deficient NK cells was considerably higher than B or T cells. These observations can be explained when mechanisms of normal lymphopoiesis are considered. Despite these quantitative and qualitative abnormalities, no patients suffered an excessive number or severity of infections. The detection of PNH clones amongst all lymphocyte lineages may provide important information regarding the natural history of the disease and additional insights into kinetics of adult lymphopoiesis.

© 1998 by The American Society of Hematology.

Pathogenesis and management of paroxysmal nocturnal haemoglobinuria

Over the past 30 years, our understanding of the pathogenesis of paroxysmal nocturnal haemoglobinuria (PNH) has increased dramatically. During that time, the events during complement activation and regulation have been described, the molecular basis for the exaggerated complement sensitivity of PNH cells has been uncovered, and the responsible gene mutation has been identified. It is now possible to relate almost all the protean manifestations of PNH to a single gene mutation in a haematopoietic stem cell. Unfortunately, our ability to manage these patients has not kept pace, and, with the exception of bone marrow transplantation, our major efforts are still directed toward control of complications rather than interruption of the disease process.

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.