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.