C5 and paroxysmal nocturnal hemoglobinuria: Eculizumab (Soliris®, Alexion Pharmaceuticals, Inc., New Haven, CT, USA) is a humanized monoclonal antibody (mAb) directed against complement C5 (C5) that has been transformative for patients with paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome, and refractory generalized myasthenia gravis [1–3].