C5 and paroxysmal nocturnal hemoglobinuria: The only approved therapeutic molecules are the plasma-derived C1 inhibitor, indicated for the treatment of hereditary angioedema (3), and the C5-blocking antibody eculizumab (Soliris), currently used to treat patients with paroxysmal nocturnal hemoglobinuria (PNH) (4) and atypical hemolytic uremic syndrome (aHUS) (5).