title: Complement fraction 3 binding on erythrocytes as additional mechanism of disease in paroxysmal nocturnal hemoglobinuria patients treated by eculizumab.
abstract: In paroxysmal nocturnal hemoglobinuria (PNH) hemolytic anemia is due mainly to deficiency of the complement regulator CD59 on the surface of red blood cells (RBCs). Eculizumab, an antibody that targets complement fraction 5 (C5), has proven highly effective in abolishing complement-mediated intravascular hemolysis in PNH; however, the hematologic benefit varies considerably among patients. In the aim to understand the basis for this variable response, we have investigated by flow cytometry the binding of complement fraction 3 (C3) on RBCs from PNH patients before and during eculizumab treatment. There was no evidence of C3 on RBCs of untreated PNH patients; by contrast, in all patients on eculizumab (n = 41) a substantial fraction of RBCs had C3 bound on their surface, and this was entirely restricted to RBCs with the PNH phenotype (CD59(-)). The proportion of C3(+) RBCs correlated significantly with the reticulocyte count and with the hematologic response to eculizumab. In 3 patients in whom (51)Cr labeling of RBCs was carried out while on eculizumab, we have demonstrated reduced RBC half-life in vivo, with excess (51)Cr uptake in spleen and in liver. Binding of C3 by PNH RBCs may constitute an additional disease mechanism in PNH, strongly enhanced by eculizumab treatment and producing a variable degree of extravascular hemolysis.
authors.affiliation: Hematology, Department of Biochemistry and Medical Biotechnologies, Federico II University, Naples, Italy. amrisita@unina.it
authors.forename: Antonio M
authors.initials: AM
authors.lastname: Risitano
authors.forename: Rosario
authors.initials: R
authors.lastname: Notaro
authors.forename: Ludovica
authors.initials: L
authors.lastname: Marando
authors.forename: Bianca
authors.initials: B
authors.lastname: Serio
authors.forename: Danilo
authors.initials: D
authors.lastname: Ranaldi
authors.forename: Elisa
authors.initials: E
authors.lastname: Seneca
authors.forename: Patrizia
authors.initials: P
authors.lastname: Ricci
authors.forename: Fiorella
authors.initials: F
authors.lastname: Alfinito
authors.forename: Andrea
authors.initials: A
authors.lastname: Camera
authors.forename: Giacomo
authors.initials: G
authors.lastname: Gianfaldoni
authors.forename: Angela
authors.initials: A
authors.lastname: Amendola
authors.forename: Carla
authors.initials: C
authors.lastname: Boschetti
authors.forename: Eros
authors.initials: E
authors.lastname: Di Bona
authors.forename: Giorgio
authors.initials: G
authors.lastname: Fratellanza
authors.forename: Filippo
authors.initials: F
authors.lastname: Barbano
authors.forename: Francesco
authors.initials: F
authors.lastname: Rodeghiero
authors.forename: Alberto
authors.initials: A
authors.lastname: Zanella
authors.forename: Anna Paola
authors.initials: AP
authors.lastname: Iori
authors.forename: Carmine
authors.initials: C
authors.lastname: Selleri
authors.forename: Lucio
authors.initials: L
authors.lastname: Luzzatto
authors.forename: Bruno
authors.initials: B
authors.lastname: Rotoli
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology* / Q000627:therapeutic use*; D061067:Antibodies, Monoclonal, Humanized; D002470:Cell Survival; D003176:Complement C3 / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism* / Q000473:pathology; D005260:Female; D005434:Flow Cytometry; D006457:Hemoglobinuria, Paroxysmal / Q000276:immunology / Q000378:metabolism* / Q000628:therapy*; D006801:Humans; D007167:Immunotherapy; D008297:Male
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D003176:Complement C3; C481642:eculizumab