title: Antilymphoma effects of anti-HLA-DR and CD20 monoclonal antibodies (Lym-1 and Rituximab) on human lymphoma cells.
abstract: OBJECTIVE
  Anti-HLA-DR and anti-CD20 monoclonal antibodies (MAbs) have been effective for immunotherapy and radioimmunotherapy in non-Hodgkin's lymphoma (NHL). The aim of our study was to compare the antilymphoma effects of Lym-1 and rituximab in human lymphoma cell lines, using assays of viability, apoptosis, antibody-dependent cellular cytotoxicity (ADCC), and complement-dependent cytotoxicity (CDC), under conditions relevant to the clinic.
  
  
  METHODS
  To characterize response relationships at varied concentrations of Lym-1 and rituximab, growth inhibition and cell death were assayed over 96 hours in four NHL cell lines derived from Burkitt's or large-cell lymphoma patients. Untreated cells and cells treated with an mLym-1 isotype-matched MAb were used as negative controls for direct assays. Western blot was used to detect apoptosis through the activation of caspase-3 and cleavage of poly (ADP-ribase) polymerase (PARP). The indirect cytotoxicity of Lym-1 and rituximab was assayed at varied concentrations, using ADCC activity in the presence of purified peripheral blood leukocytes and CDC activity in the presence of human donor serum.
  
  
  RESULTS
  Lym-1 and rituximab showed significant direct and indirect antilymphoma effects. Lym-1 had a substantial, and statistically greater, effect than rituximab over longer intervals of time. In Raji and B35M cells, Lym-1 induced potent growth inhibition reflected by 90% and 94% reductions in viable cells, respectively, whereas rituximab induced 63% and 56% reductions. Concurrently, Lym-1 increased nonviable cells by 372% and 153% in these cells, respectively, whereas rituximab induced 139% and 43% increases. Lym-1-induced apoptosis was greater than that of rituximab in all cell lines tested. Lym-1, both the chimeric form and the mouse parent, mediate ADCC more effectively, in the presence of a total peripheral blood leukocyte (PBL) population, than does rituximab, although the results for CDC activity were mixed.
  
  
  CONCLUSIONS
  In conclusion, Lym-1 had more potent direct and indirect cytotoxic effects than rituximab in lymphoma cells under conditions achievable in patients. Because the HLA-DR target antigen of Lym-1 is enriched on most B-cell lymphomas, these results support its complementary use in patients as an alternative to CD20 for monoimmunotherapy and for combination immunotherapy with rituximab, because the HLA-DR and CD20 antigens are physically and functionally coupled on human B cells.
authors.affiliation: Department of Internal Medicine, University of California-Davis, Davis, CA, USA.
authors.forename: Cathy
authors.initials: C
authors.lastname: Liu
authors.forename: Gerald
authors.initials: G
authors.lastname: DeNardo
authors.forename: Evan
authors.initials: E
authors.lastname: Tobin
authors.forename: Sally
authors.initials: S
authors.lastname: DeNardo
mesh_terms: D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20 / Q000276:immunology*; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D017209:Apoptosis; D015153:Blotting, Western; D002051:Burkitt Lymphoma / Q000188:drug therapy; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D003165:Complement System Proteins; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D006684:HLA-DR Antigens / Q000276:immunology*; D006801:Humans; D007167:Immunotherapy / Q000379:methods*; D007962:Leukocytes / Q000166:cytology; D008223:Lymphoma / Q000188:drug therapy*; D016403:Lymphoma, Large B-Cell, Diffuse / Q000188:drug therapy; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D000069283:Rituximab; D013997:Time Factors
chemical_list: D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D000970:Antineoplastic Agents; D006684:HLA-DR Antigens; C410509:Lym-1 monoclonal antibody; D000069283:Rituximab; D003165:Complement System Proteins; D011065:Poly(ADP-ribose) Polymerases; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases