Mechanism of action of type II, glycoengineered, anti-CD20 monoclonal antibody GA101 in B-chronic lymphocytic leukemia whole blood assays in comparison with rituximab and alemtuzumab

J Immunol. 2011 Mar 15;186(6):3762-9. doi: 10.4049/jimmunol.1000303. Epub 2011 Feb 4.


We analyzed in B-chronic lymphocytic leukemia (B-CLL) whole blood assays the activity of therapeutic mAbs alemtuzumab, rituximab, and type II glycoengineered anti-CD20 mAb GA101. Whole blood samples were treated with Abs, and death of CD19(+) B-CLL was measured by flow cytometry. Alemtuzumab efficiently lysed B-CLL targets with maximal lysis at 1-4 h (62%). In contrast, rituximab induced a more limited cell death (21%) that was maximal only at 24 h. GA101 killed B-CLL targets to a similar extent but more rapidly than rituximab, with 19.2 and 23.5% cell death at 4 and 24 h, respectively, compared with 7.9 and 21.4% for rituximab. Lysis by both rituximab and GA101 correlated directly with CD20 expression levels (r(2) = 0.88 and 0.85, respectively). Interestingly, lysis by all three Abs at high concentrations was mostly complement dependent, because it was blocked by the anti-C5 Ab eculizumab by 90% in the case of alemtuzumab and rituximab and by 64% in the case of GA101. Although GA101 caused homotypic adhesion, it induced only limited (3%) direct cell death of purified B-CLL cells. Both rituximab and GA101 showed the same efficiency in phagocytosis assays, but phagocytosis was not significant in whole blood due to excess Igs. Finally, GA101 at 1-100 μg/ml induced 2- to 3-fold more efficient NK cell degranulation than rituximab in isolated B-CLL or normal PBMCs. GA101, but not rituximab, also mediated significant NK cell degranulation in whole blood samples. Thus, complement and Ab-dependent cellular cytotoxicity are believed to be the major effector mechanisms of GA101 in whole blood assays.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alemtuzumab
  • Antibodies, Monoclonal / blood
  • Antibodies, Monoclonal / pharmacology*
  • Antibodies, Monoclonal / therapeutic use
  • Antibodies, Monoclonal, Humanized
  • Antibodies, Monoclonal, Murine-Derived / blood
  • Antibodies, Monoclonal, Murine-Derived / pharmacology*
  • Antibodies, Monoclonal, Murine-Derived / therapeutic use
  • Antibodies, Neoplasm / blood
  • Antibodies, Neoplasm / pharmacology*
  • Antibodies, Neoplasm / therapeutic use
  • Antigens, CD20 / immunology*
  • Complement System Proteins / physiology
  • Cytotoxicity Tests, Immunologic / methods
  • Dose-Response Relationship, Immunologic
  • Humans
  • Leukemia, Lymphocytic, Chronic, B-Cell / blood
  • Leukemia, Lymphocytic, Chronic, B-Cell / immunology*
  • Leukemia, Lymphocytic, Chronic, B-Cell / therapy*
  • Protein Engineering / methods*
  • Rituximab
  • Tumor Cells, Cultured


  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Humanized
  • Antibodies, Monoclonal, Murine-Derived
  • Antibodies, Neoplasm
  • Antigens, CD20
  • Alemtuzumab
  • Rituximab
  • Complement System Proteins
  • obinutuzumab