Apoptosis of Malignant Human B Cells by Ligation of CD20 With Monoclonal Antibodies

Abstract

CD20 is a nonglycosylated 33 to 37 kD phosphoprotein involved in B-cell signaling that subserves important functions in the regulation of B-cell proliferation and differentiation. In addition, this B-cell surface antigen has been shown recently to be an effective target for immunotherapy of B-cell malignancies using chimeric (mouse/human) or radiolabeled murine monoclonal anti-CD20 antibodies. In this report we show that extensive crosslinking of CD20 with murine anti-CD20 monoclonal antibodies (MoAbs) in the presence of either goat anti-mouse IgG or Fc receptor (FcR)-expressing cells directly inhibits B-cell proliferation, induces nuclear DNA fragmentation, and leads to cell death by apoptosis. The apoptotic effects of these MoAbs can be inhibited by chelation of extracellular or intracellular Ca 2؉ by EGTA orBapta AM, indicating that anti-CD20-mediated apoptosis may be related to changes in Ca 2؉ concentration. These findings suggest that ligation of CD20 in vivo by anti-CD20 antibodies in the presence of FcR-expressing cells may initiate signal transduction events that induce elevation of [Ca 2؉ ] i and lead to apoptosis of malignant B cells, thereby contributing to the impressive tumor regressions observed in mouse models and clinical trials using anti-CD20 MoAbs.

Binding of HIV-1 gp120 to DC-SIGN Promotes ASK-1-Dependent Activation-Induced Apoptosis of Human Dendritic Cells

“…S12). Turning to upstream components that may account for these observations and explain excessive apoptosis, we found that gp120 binding activated Raf-1, an anti-apoptotic through its activity to restrict caspase activation [41], as reported by others [22], and its expression was not significantly modulated upon exposure to maturation stimuli (Fig. 7A).…”

“…We adopted two approaches: removing the carbohydrate moieties of recombinant gp120 by EndoH (endo-b-N-glucosaminidase) before cross-linking with anti-''tag'' Abs, and pretreating DC with mannan to compete off the gp120 binding. Because DC express abundant FcR [40] and FcR cross-linking may induce apoptosis of certain cells [41,42,43], we also investigated the effect of FcR blockade prior to gp120 pulsing. After EndoH treatment, the deglycosylated monomeric gp120 had reduced molecular weight (<80 kDa, reduced from <120 kDa), and after cross-linking in dimeric form, they indeed lost their binding capacity to moDC ( Fig.…”

Enhanced killing of B lymphoma cells by granulocyte colony‐stimulating factor‐primed effector cells and Hu1D10 – a humanized human leucocyte antigen DR antibody

“…Apoptosis induction, however, required hyper-crosslinking with secondary antibody. For CD20, it is well documented in the literature that hyper-crosslinking can also be provided by Fc-receptor-expressing cells (Shan et al, 1998). Therefore, it appears conceivable that G-CSF-primed PMN may function as crosslinking cells in vivo.…”

Growth Inhibition of CD20‐positive B Lymphoma Cell Lines by IDEC‐C2B8 Anti‐CD20 Monoclonal Antibody

“…31,32) A recent report by Shan et al also demonstrated that the B1 antibody (detecting a different CD20 epitope) needed to be cross-linked to induce apoptosis of Burkitt cell lines. 33) Although the sequence of events was different for different anti-CD20 monoclonal antibodies, the available evidence suggests that the CD20 molecule is involved in the programmed cell death pathway.…”