CD55 and paroxysmal nocturnal hemoglobinuria: A derivative of this original peptide, pegcetacoplan, received fast-track and orphan drug approval in July 2022 for the indication of paroxysmal nocturnal hemoglobinuria (PNH), a rare genetic disorder caused by aberrant glycosylphosphatidylinositol (GPI) conformation causing deficient expression of CD55 and CD59 and unconstrained MAC-induced hemolysis.