title: Overexpression of protectin (CD59) down-modulates the susceptibility of human melanoma cells to homologous complement.
abstract: The clinical efficacy of therapeutic complement (C)-activating monoclonal antibodies (mAb) to melanoma-associated antigens can be impaired by the levels of expression of C-inhibitory molecules on neoplastic cells. Protectin (CD59) is a glycosylphosphatidylinositol (GPI)-anchored cell membrane glycoprotein, acting as terminal regulator of C cascade, which is heterogeneously expressed in melanomas and represents the main restriction factor of C-mediated lysis of melanoma cells. Thus, we investigated whether the overexpression of CD59 could influence the constitutive susceptibility of distinct melanoma cells to homologous C. Infection of CD59-positive Mel 100 and 70-W melanoma cells by a retroviral vector carrying the CD59 cDNA, significantly (P < 0.05) upregulated their constitutive expression of CD59, whereas it did not affect that of additional C-regulatory molecules. Transduced CD59 was entirely GPI-anchored and showed a molecular weight identical to native CD59. Additionally, higher amounts of soluble CD59 were detected in the conditioned media of CD59-transduced melanoma cells compared with parental cells. CD59-transduced melanoma cells, sensitized by the anti-GD3 disialoganglioside mAb R24, were significantly (P < 0.05) less susceptible to homologous C-lysis than were parental cells; this effect was fully reverted by the masking of CD59 with F(ab')(2) fragments of the anti-CD59 mAb YTH53.1. These results provide conclusive evidence demonstrating that absolute levels of CD59 expression regulate the susceptibility to homologous C of specific melanoma cells, and suggest an additional explanation for the poor clinical results obtained with C-activating mAb in the clinical setting.
authors.affiliation: Advanced Immunotherapy Unit, Centro di Riferimento Oncologico, Istituto Nazionale di Ricovero e Cura a Carattere Scientifico, Aviano, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Coral
authors.forename: E
authors.initials: E
authors.lastname: Fonsatti
authors.forename: L
authors.initials: L
authors.lastname: Sigalotti
authors.forename: C
authors.initials: C
authors.lastname: De Nardo
authors.forename: A
authors.initials: A
authors.lastname: Visintin
authors.forename: G
authors.initials: G
authors.lastname: Nardi
authors.forename: F
authors.initials: F
authors.lastname: Colizzi
authors.forename: M P
authors.initials: MP
authors.lastname: Colombo
authors.forename: G
authors.initials: G
authors.lastname: Romano
authors.forename: M
authors.initials: M
authors.lastname: Altomonte
authors.forename: M
authors.initials: M
authors.lastname: Maio
mesh_terms: D018957:CD59 Antigens / Q000096:biosynthesis / Q000235:genetics*; D003167:Complement Activation / Q000235:genetics*; D015536:Down-Regulation; D015972:Gene Expression Regulation, Neoplastic / Q000276:immunology; D005822:Genetic Vectors; D006801:Humans; D008545:Melanoma / Q000235:genetics* / Q000276:immunology*; D012190:Retroviridae; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D018957:CD59 Antigens