Signaling events involved in anti-CD20-induced apoptosis of malignant human B cells

Cancer Immunol Immunother. 2000 Mar;48(12):673-83. doi: 10.1007/s002620050016.


Anti-CD20 monoclonal antibodies have been successfully employed in the clinical treatment of non-Hodgkin's lymphomas in both unmodified and radio-labeled forms. Previous publications have demonstrated that the antitumor effects of unmodified anti-CD20 mAb are mediated by several mechanisms including antibody-dependent cellular cytotoxicity, complement-mediated cell lysis, and induction of apoptosis by CD20 cross-linking. In this report, we demonstrate induction of apoptosis by three anti-CD20 monoclonal antibodies [1F5, anti-B1, and C2B8 (Rituximab)]. The magnitude of apoptosis induction was greater with the chimeric Rituximab antibody than with the murine 1F5 and anti-B1 antibodies. Apoptosis could be enhanced with any of the antibodies by cross-linking with secondary antibodies (or Fc-receptor-bearing accessory cells). The signaling events involved in anti-CD20-induced apoptosis were investigated, including activation of protein tyrosine kinases, increases in intracellular Ca2+ concentrations, caspase activation, and cleavage of caspase substrates. Our results indicate that anti-CD20-induced apoptosis can be attenuated by PP1, an inhibitor of protein tyrosine kinases Lck and Fyn, chelators of extracellular or intracellular Ca2+, and inhibitors of caspases, suggesting that anti-CD20-induced apoptosis may involve modulation of these signaling molecules. We also demonstrated that varying the expression of Bc1-2 did not affect the magnitude of anti-B1-induced apoptosis, possibly because of the sequestering effects of other Bc1-2 family members, such as Bad. These studies identify several of the signal-transduction events involved in the apoptosis of malignant B cells that transpire following ligation of CD20 by anti-CD20 antibodies in the presence of Fc-receptor-expressing cells or secondary goat anti-(mouse Ig) antibodies and which may contribute to the tumor regressions observed in mouse models and clinical trials.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Chloromethyl Ketones / pharmacology
  • Animals
  • Antibodies, Monoclonal / pharmacology*
  • Antibodies, Monoclonal, Murine-Derived
  • Antigens, CD20 / immunology
  • Antigens, CD20 / physiology*
  • Apoptosis* / drug effects
  • B-Lymphocytes / pathology*
  • Burkitt Lymphoma / immunology
  • Burkitt Lymphoma / pathology*
  • Calcium / pharmacology
  • Calcium Signaling
  • Carrier Proteins / physiology
  • Caspases / pharmacology
  • Chelating Agents / pharmacology
  • Cysteine Proteinase Inhibitors / pharmacology
  • Enzyme Activation
  • Humans
  • Immunoglobulin Fc Fragments / immunology
  • Ionomycin / pharmacology
  • Lymphoma, B-Cell / immunology
  • Lymphoma, B-Cell / pathology*
  • Lymphoma, T-Cell / immunology
  • Lymphoma, T-Cell / pathology
  • Mice
  • Phosphoprotein Phosphatases / pharmacology
  • Phosphorylation / drug effects
  • Poly(ADP-ribose) Polymerases / metabolism
  • Protein Processing, Post-Translational / drug effects
  • Protein-Tyrosine Kinases / antagonists & inhibitors
  • Protein-Tyrosine Kinases / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / physiology
  • Receptor Aggregation
  • Recombinant Fusion Proteins / pharmacology
  • Rituximab
  • Signal Transduction*
  • Tumor Cells, Cultured
  • bcl-Associated Death Protein
  • fas Receptor / physiology


  • Amino Acid Chloromethyl Ketones
  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Murine-Derived
  • Antigens, CD20
  • BAD protein, human
  • Bad protein, mouse
  • Carrier Proteins
  • Chelating Agents
  • Cysteine Proteinase Inhibitors
  • Immunoglobulin Fc Fragments
  • Proto-Oncogene Proteins c-bcl-2
  • Recombinant Fusion Proteins
  • bcl-Associated Death Protein
  • benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone
  • fas Receptor
  • Rituximab
  • Ionomycin
  • Poly(ADP-ribose) Polymerases
  • Protein-Tyrosine Kinases
  • Phosphoprotein Phosphatases
  • Caspases
  • Calcium