Activated platelets in paroxysmal nocturnal haemoglobinuria

Summary. One of the major causes of morbidity and mortality in paroxysmal nocturnal haemoglobinuria (PNH) is venous thrombosis. We have studied fibrinolysis, coagulation and platelets in 11 patients with PNH in an attempt to identify the possible mechanism(s) of thrombosis in PNH. In this study we did not identify any fibrinolytic defects, evidence of coagulation activation, nor reduction in coagulation inhibitors. In contrast, in this cohort of 11 PNH patients we have identified varying degrees of platelet activation as defined by the surface expression of activation dependent proteins and the binding of adhesive proteins to the platelet surface. The thrombotic events in PNH usually occur in the venous system. Our studies and previous experimental studies suggest that anti-platelet therapy may be efficacious in reducing the incidence and severity of venous thrombosis in PNH.     

Bone marrow transplants for paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare clonal haematological disorder characterized by intravascular haemolysis and increased risk of thrombosis. PNH is associated with bone marrow failure syndromes including aplastic anaemia, myelodysplasia and leukaemia. Bone marrow transplants are sometimes used to treat PNH, but small series and reporting biases make assessment of transplant outcome difficult. The outcome of 57 consecutive allogeneic bone marrow transplants for PNH reported to the International Bone Marrow Transplant Registry (IBMTR) between 1978 and 1995 was analysed. The 2-year probability of survival in 48 recipients of HLA-identical sibling transplants was 56% (95% confidence interval 49-63%). Two recipients of identical twin transplants remain alive 8 and 12 years after treatment. One of seven recipients of alternative donor allogeneic transplants is alive 5 years after transplant. The most common causes of treatment failure were graft failure and infections. Our results indicate that bone marrow transplantation can restore normal bone marrow function in about 50% of PNH patients.     

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.     

Bone marrow transplantation for paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is an acquired clonal disorder of the haemopoietic stem cells for which the only curative treatment is bone marrow transplantation. There are few reports on the use of allogeneic transplantation for PNH, and nearly all of them include only a few patients. Between September 1978 and December 1997, 16 patients underwent marrow transplantation for PNH at the Hospital Saint Louis. The 5-year survival rate for the 16 patients was 58 +/- 13%. Two factors, an absolute neutrophil count >1.0 x 109/l and haemoglobin level >9 g/dl at transplant, were found to be statistically associated with a better outcome.     

Long‐term safety and efficacy of sustained eculizumab treatment in patients with paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is characterized by chronic, uncontrolled complement activation resulting in elevated intravascular haemolysis and morbidities, including fatigue, dyspnoea, abdominal pain, pulmonary hypertension, thrombotic events (TEs) and chronic kidney disease (CKD). The long‐term safety and efficacy of eculizumab, a humanized monoclonal antibody that inhibits terminal complement activation, was investigated in 195 patients over 66 months. Four patient deaths were reported, all unrelated to treatment, resulting in a 3‐year survival estimate of 97·6%. All patients showed a reduction in lactate dehydrogenase levels, which was sustained over the course of treatment (median reduction of 86·9% at 36 months), reflecting inhibition of chronic haemolysis. TEs decreased by 81·8%, with 96·4% of patients remaining free of TEs. Patients also showed a time‐dependent improvement in renal function: 93·1% of patients exhibited improvement or stabilization in CKD score at 36 months. Transfusion independence increased by 90·0% from baseline, with the number of red blood cell units transfused decreasing by 54·7%. Eculizumab was well tolerated, with no evidence of cumulative toxicity and a decreasing occurrence of adverse events over time. Eculizumab has a substantial impact on the symptoms and complications of PNH and results a significant improvement in patient survival.     

Update on paroxysmal nocturnal haemoglobinuria: on the long way to understand the principles of the disease

The understanding of the clinical manifestations in paroxysmal nocturnal haemoglobinuria (PNH) has made great progress. The main symptoms of this disease such as abdominal pain, renal failure or pulmonary hypertension and even the basis of the dramatic thrombophilia can be related to intravascular haemolysis and liberation of free haemoglobin resulting in NO depletion. In addition, there has been a recent great progress in elucidating the pathophysiology of clonal expansion within PNH bone marrow. In the majority of patients with haemolytic PNH, there are additional mutations within genes beyond PIG‐A and rather affecting growth and differentiation of clonal bone marrow cells. In contrast to the formerly proposed single mechanism hypotheses such as immune selection or intrinsic gain of clonal dominance, this appears to follow a pattern of a complex clonal hierarchy putatively integrating both earlier anticipated mechanisms. Treatment of PNH is mainly supportive. The only curative approach as allogeneic stem cell transplantation should only be applied to patients with complications such as secondary bone marrow aplasia or transformation into MDS or AML. Symptomatic haemolytic PNH will be treated with eculizumab, an inhibitor of the terminal complement cascade. Treatment with eculizumab can significantly prevent PNH‐related symptoms including the abnormal thrombophilia. Recently, it was demonstrated that in contrast to untreated historic PNH patients, meanwhile a normal life expectancy is observed in eculizumab‐treated patients. The recently approved vaccine against meningococci type B by the European Medical Agency (EMA) could probably further help to prevent meningococcal sepsis due to the induced complement deficiency by eculizumab.     

Cytogenetic and morphological abnormalities in paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is characterized by the expansion of a haematopoietic stem cell clone with a PIG-A mutation (the PNH clone) in an environment in which normal stem cells are lost or failing: it has been hypothesized that this abnormal marrow environment provides a relative advantage to the PNH clone. In patients with PNH, generally, the karyotype of bone marrow cells has been reported to be normal, unlike in myelodysplastic syndrome (MDS), another clonal condition in which cytogenetic abnormalities are regarded as diagnostic. In a retrospective review of 46 patients with a PNH clone, we found a karyotypic abnormality in 11 (24%). Upon follow-up, the proportion of cells with abnormal karyotype decreased significantly in seven of these 11 patients. Abnormal morphological bone marrow features reminiscent of MDS were common in PNH, regardless of the karyotype. However, none of our patients developed excess blasts or leukaemia. We conclude that in patients with PNH cytogenetically abnormal clones are not necessarily malignant and may not be predictive of evolution to leukaemia.     

Pathophysiology,diagnosis, and treatment of paroxysmal nocturnal hemoglobinuria: a review

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired disorder of the hematopoietic stem cell that makes blood cells more sensitive to the action of complement. Patients experience intravascular hemolysis, smooth muscle dystonia, renal failure, arterial and pulmonary hypertension, recurrent infectious diseases and an increased risk of notably dreadful thrombotic complications. The diagnosis is made by flow cytometry. Efforts have been recently performed to improve the sensitivity and the standardization of this technique. PNH is frequently associated with aplastic anemia or low‐risk myelodysplasia and may be asymptomatic. Management of the classical form of PNH has been dramatically revolutionized by the development of eculizumab, which brings benefits in terms of hemolysis, quality of life, renal function, thrombotic risk, and life expectancy. Prophylaxis and treatment of arterial and venous thrombosis currently remain a challenge in PNH.     

NKG2D-mediated immunity underlying paroxysmal nocturnal haemoglobinuria and related bone marrow failure syndromes

It is considered that a similar immune mechanism acts in the pathogenesis of bone marrow (BM) failure in paroxysmal nocturnal haemoglobinuria (PNH) and its related disorders, such as aplastic anaemia (AA) and myelodysplastic syndromes (MDS). However, the molecular events in immune-mediated marrow injury have not been elucidated. We recently reported an abnormal expression of stress-inducible NKG2D (natural-killer group 2, member D) ligands, such as ULBP (UL16-binding protein) and MICA/B (major histocompatibility complex class I chain-related molecules A/B), on granulocytes in some PNH patients and the granulocyte killing by autologous lymphocytes in vitro. The present study found that the expression of NKG2D ligands was common to both granulocytes and BM cells of patients with PNH, AA, and MDS, indicating their exposure to some incitement to induce the ligands. The haematopoietic colony formation in vitro by the patients' marrow cells significantly improved when their BM cells were pretreated with antibodies against NKG2D receptor, suggesting that the antibodies rescued haematopoietic cells expressing NKG2D ligands from damage by autologous lymphocytes with NKG2D. Clinical courses of patients with PNH and AA showed a close association of the expression of NKG2D ligands with BM failure and a favourable response to immunosuppressive therapy. We therefore propose that NKG2D-mediated immunity may underlie the BM failure in PNH and its-related marrow diseases.     

The management of pregnancy in paroxysmal nocturnal haemoglobinuria on long term eculizumab

In Paroxysmal nocturnal haemoglobinuria (PNH), pregnancy is associated with increased maternal and foetal complications to such an extent that the condition has been considered relatively contra‐indicated in PNH. Eculizumab has revolutionized the treatment of PNH. We evaluate its use in pregnancy to date. We report on seven patients exposed to eculizumab at different stages of pregnancy including the first two patients to receive the drug from conception to delivery. There was no evidence of complement blockade from cord blood samples taken at delivery. Eculizumab appears safe to use in this setting and is likely to prevent many of the complications usually observed.     

Pharmacokinetic and pharmacodynamic effects of ravulizumab and eculizumab on complement component 5 in adults with paroxysmal nocturnal haemoglobinuria: results of two phase 3 randomised,multicentre studies

Ravulizumab, a novel long-acting complement component 5 (C5) inhibitor administered every 8 weeks (q8w), was non-inferior to eculizumab for all efficacy outcomes in two randomised, open-label, phase 3 trials in C5 inhibitor-naïve (Study 301) and eculizumab-experienced (Study 302) adult patients with paroxysmal nocturnal haemoglobinuria (PNH). This pre-specified analysis characterised ravulizumab pharmacokinetics (PK), pharmacodynamics (PD; free C5 levels), and PD differences between medications (Study 301, n = 246; Study 302, n = 195). Ravulizumab PK parameters were determined using non-compartmental analysis. Serum free C5 was quantified with a Gyros-based fluorescence assay (ravulizumab) and an electrochemiluminescence ligand-binding assay (eculizumab). Ravulizumab PK parameters were numerically comparable in both studies; the median time to maximum concentrations ranged from 2·3 to 2·8 and 2·3 to 2·6 h in studies 301 and 302, respectively. Ravulizumab steady-state serum concentrations were achieved immediately after the first dose and sustained throughout treatment. For ravulizumab, the mean (SD) post hoc terminal elimination half-life was 49·7 (8·9) days. Serum free C5 concentrations <0·5 µg/ml were achieved after the first ravulizumab dose and sustained throughout treatment in both studies. In a minority of patients, free C5 concentrations <0·5 µg/ml were not consistently achieved with eculizumab in either study. Ravulizumab q8w was more consistent in providing immediate, complete, sustained C5 inhibition than eculizumab every-2-weeks in patients with PNH.     

Eculizumab, a terminal complement inhibitor, improves anaemia in patients with paroxysmal nocturnal haemoglobinuria

In paroxysmal nocturnal haemoglobinuria (PNH), chronic destruction of PNH red blood cells (RBCs) by complement leads to anaemia and other serious morbidities. Eculizumab inhibits terminal complement-mediated PNH RBC destruction by targeting C5. In the phase III, double-blind, placebo-controlled, TRIUMPH study, eculizumab reduced haemolysis, stabilized haemoglobin levels, reduced transfusion requirements and improved fatigue in patients with PNH. Herein, we explored the effects of eculizumab on measures of anaemia in patients from the TRIUMPH study and the open-label SHEPHERD study, a more heterogeneous population. Eculizumab reduced haemolysis regardless of pretreatment transfusion requirements and regardless of whether or not patients became transfusion-dependent during treatment ( P  <   0·001). Reduction in haemolysis was associated with increased PNH RBC counts ( P  <   0·001) while reticulocyte counts remained elevated. Eculizumab-treated patients demonstrated significantly higher levels of haemoglobin as compared with placebo in TRIUMPH and relative to baseline levels in SHEPHERD ( P  <   0·001 for each study). Eculizumab lowered transfusion requirement across multiple pretreatment transfusion strata and eliminated transfusion support in a majority of both TRIUMPH and SHEPHERD patients ( P  <   0·001). Patients who required some transfusion support during treatment with eculizumab showed a reduction in haemolysis and transfusion requirements and an improvement in fatigue. Eculizumab reduces haemolysis and improves anaemia and fatigue, regardless of transfusion requirements.     

Treatment of paroxysmal nocturnal hemoglobinuria in the era of eculizumab

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, life-threatening and debilitating clonal blood disorder caused by an acquired mutation in the phosphatidylinositol glycan (PIG)-A gene. In pluripotent hematopoietic stem cells, this leads to a deficiency of glycosylphosphatidylinositol (GPI)-anchors and GPI-anchored proteins, including the complement regulators CD55 and CD59, on the surface of affected blood cells. PNH red blood cells are highly vulnerable to activation of complement and the formation of the membrane attack complex (MAC). The resulting chronic intravascular hemolysis is the underlying cause of PNH morbidities and mortality. Until recently, the treatment of PNH has been largely empirical and symptomatic with blood transfusions, anticoagulation, and supplementation with folic acid or iron. The only potentially curative treatment is allogeneic stem cell transplantation, but this has severe complications and high mortality and morbidity rates. A new targeted and disease-modifying treatment strategy is the inhibition of the terminal complement cascade with the humanized monoclonal anti-C5 antibody, eculizumab. This effectively inhibits MAC formation and intravascular hemolysis. Eculizumab has shown significant efficacy in controlled studies, with a marked decrease in anemia, fatigue, transfusion requirements, renal impairment, pulmonary hypertension, and risk of severe thromboembolic events, ultimately resulting in improving quality of life and survival.