Agonists of the TNF superfamily of receptors hold promise as novel therapy for cancer. Recent data based on agonistic anti-murine CD40 and other TNF receptors suggest a requirement for specific Fc-receptor engagement for optimal biological and anti-tumor effects. This has prompted calls to engineer anti-human CD40 and other TNF receptor mAb accordingly. The agonistic anti-human CD40 mAb CP-870,893 is a fully human IgG2 immunoglobulin, selected in part because of presumed poor reactivity with Fc receptors, yet in multiple clinical trials, this mAb has been shown to have activity in patients with melanoma, pancreatic and other cancers. Here, we reproduced findings that anti-murine CD40 mAb depend on FcγRIIB engagement, demonstrating enhanced activation of antigen presenting cells upon Fc crosslinking of anti-mouse CD40 mAb and decreased activity in FcγRIIB-/- mice. In contrast, CP-870,893-mediated activation of human B cells was neither enhanced with anti-IgG crosslinking nor abrogated with an F(ab)'2 reagent. Crosslinking of CP-870,893 using CD32-expressing K562 cells yielded an Fc-dependent modest increase in expression of some activation markers relative to 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 in contrast to the IgG1 anti-CD20 mAb rituximab which mediated both ADCC and CMC in parallel assays. Mouse CD40 mAb competed for the CD40 ligand binding site, in contrast to CP-870,893. Thus, Fc crosslinking is not an essential requirement for agonistic anti-human CD40 mAb; potency is more dependent on the CD40 epitope recognized and the strength of the signal achieved.
- Received September 13, 2013.
- Revision received October 24, 2013.
- Accepted October 25, 2013.
- Copyright © 2013, American Association for Cancer Research.