PDF file - 72K, Supplementary Figure 2. Dose-dependent B cell activation with CP-870,893 and its F(ab)'2 fragment.
ARTICLE ABSTRACTAgonists of the TNF superfamily of receptors hold promise as novel therapy for cancer. Recent data on agonistic antimurine TNF receptors (TNFR) such as CD40 suggest that the specific engagement of Fc receptor (FcR) is required for optimal antitumor effects, prompting calls to engineer antihuman CD40 and other TNFR monoclonal antibodies (mAb) accordingly. CP-870,893 is a fully human anti-CD40 mAb, selected in part because it is an immunoglobulin G2 (IgG2), which is presumed to have poor reactivity with FcR; however, CP-870,893 has been evaluated in multiple clinical trials with beneficial activity in patients with melanoma, pancreatic, and other cancers. Here, we confirmed that the activity of antimurine CD40 mAb was dependent on FcγRIIB engagement, was decreased significantly in FcγRIIB−/− mice, and upon Fc-crosslinking antimouse CD40 mAb enhanced the activation of antigen-presenting cells. In contrast, the CP-870,893-mediated activation of human B cells was not enhanced with anti-IgG crosslinking nor abrogated when used as an F(ab)′2 reagent. Crosslinking of CP-870,893 using the CD32-expressing K562 cells yielded an Fc-dependent modest increase in the expression of some activation markers relative to that of the soluble CP-870,893 mAb. Classic Fc-dependent functions such as antibody-dependent cellular cytotoxicity (ADCC) and complement-mediated cytotoxicity (CMC) were minimal for CP-870,893 as compared with the IgG1 anti-CD20 mAb rituximab, which mediated both ADCC and CMC in parallel assays. Antimouse CD40 mAb competed for the CD40 ligand binding site, but CP-870,893 did not. Thus, Fc crosslinking is not an essential requirement for agonistic antihuman CD40 mAbs, in which potency is more dependent on the CD40 epitope recognized and the strength of the signal achieved. Cancer Immunol Res; 2(1); 19–26. ©2013 AACR.