title: rILYd4, a human CD59 inhibitor, enhances complement-dependent cytotoxicity of ofatumumab against rituximab-resistant B-cell lymphoma cells and chronic lymphocytic leukemia.
abstract: OBJECTIVE
  Ofatumumab is an anti-CD20 antibody recently approved for treatment of fludarabine and alemtuzumab refractory chronic lymphocytic leukemia (CLL); it mediates much stronger complement-dependent cytotoxicity (CDC) than rituximab. Human CD59, a key membrane complement regulator that inhibits CDC, is highly expressed in B-cell malignancies and its upregulation is an important determinant of the sensitivity of B-cell malignancies to rituximab treatment. Previously, we have shown that the potent CD59 inhibitor rILYd4 sensitizes rituximab-resistant lymphoma cells to rituximab-mediated CDC. Here, we further investigated whether rILYd4 can sensitize B-cell malignancies to ofatumumab-mediated CDC and whether either ofatumumab-mediated CDC or rILYd4-enhanced ofatumumab-mediated CDC correlates with CD20 or CD59 expression, known biomarkers involved in rituximab activity.
  
  
  METHODS
  Rituximab-resistant cell lines and primary CLL cells were used to investigate the antitumor efficacy of the combination of rILYd4 with ofatumumab or rituximab. Propidium iodide staining or alamarBlue assay were used to evaluate the CDC effect. The levels of CD20 and CD59 on the cell membrane were analyzed by flow cytometry.
  
  
  RESULTS
  rILYd4 enhanced CDC effects mediated by ofatumumab or rituximab on rituximab-resistant lymphoma cells and primary CLL cells in vitro. The sensitivity to CDC effects mediated by ofatumumab positively correlated with the ratio of CD20/CD59 and negatively correlated with CD59 levels on CLL cells. The degree to which rILYd4 enhanced CDC correlated positively with the CD59 levels on CLL cells.
  
  
  CONCLUSIONS
  These data suggest that rILYd4 may enhance the anticancer activity of ofatumumab and rituximab in B-cell malignancies that have relapsed after prior antibody-based therapies.
authors.affiliation: Center for Molecular Medicine, the First Affiliated Hospital, School of Medicine, Xi'an Jiaotong University, Xi'an, China.
authors.forename: Xiaowen
authors.initials: X
authors.lastname: Ge
authors.forename: Lin
authors.initials: L
authors.lastname: Wu
authors.forename: Weiguo
authors.initials: W
authors.lastname: Hu
authors.forename: Stacey
authors.initials: S
authors.lastname: Fernandes
authors.forename: Chun
authors.initials: C
authors.lastname: Wang
authors.forename: Xu
authors.initials: X
authors.lastname: Li
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Brown
authors.forename: Xuebin
authors.initials: X
authors.lastname: Qin
mesh_terms: D000911:Antibodies, Monoclonal / Q000008:administration & dosage / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D058846:Antibodies, Monoclonal, Murine-Derived / Q000008:administration & dosage; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D001430:Bacteriocins / Q000008:administration & dosage / Q000494:pharmacology*; D018957:CD59 Antigens / Q000276:immunology* / Q000378:metabolism; D045744:Cell Line, Tumor; D003165:Complement System Proteins / Q000276:immunology; D003602:Cytotoxicity, Immunologic / Q000187:drug effects; D004357:Drug Synergism; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy* / Q000276:immunology; D016393:Lymphoma, B-Cell / Q000188:drug therapy* / Q000276:immunology; D010446:Peptide Fragments / Q000008:administration & dosage; D017434:Protein Structure, Tertiary; D000069283:Rituximab
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D058846:Antibodies, Monoclonal, Murine-Derived; D001430:Bacteriocins; D018957:CD59 Antigens; D010446:Peptide Fragments; C403910:intermedilysin protein, Streptococcus intermedius; C051590:CD59 protein, human; D000069283:Rituximab; D003165:Complement System Proteins; C527517:ofatumumab