Purpose: EGFR is highly overexpressed on several cancers and two targeted anti-EGFR antibodies which differ by isotype are FDA approved for clinical use. Cetuximab (IgG1 isotype) inhibits downstream signaling of EGFR and activates anti-tumor, cellular immune mechanisms. As panitumumab (IgG2 isotype) may inhibit downstream EGFR signaling similar to cetuximab, it might also induce adaptive immunity. Experimental Design: We measured in vitro activation of cellular components of the innate and adaptive immune system. We also studied the in vivo activation of components of the adaptive immune system in patient specimens from two recent clinical trials using cetuximab or panitumumab. Results: Both mAb primarily activate NK cells, although cetuximab is significantly more potent than panitumumab. Cetuximab-activated neutrophils mediate ADCC against HNSCC tumor cells, and interestingly, this effect was FcγRIIa and FcγRIIIa genotype dependent. Panitumumab may activate monocytes through CD32 (FcγRIIa), however monocytes activated by either mAb are not able to mediate ADCC. Cetuximab enhanced DC maturation to a greater extent than panitumumab, which was associated with improved tumor antigen cross presentation by cetuximab compared with panitumumab. This correlated with increased EGFR-specific cytotoxic CD8+ T cells in patients treated with cetuximab compared to those treated with panitumumab. Conclusions: Although panitumumab effectively inhibits EGFR signaling to a similar extent as cetuximab, it is less effective at triggering anti-tumor, cellular immune mechanisms which may be crucial for effective therapy of HNSCC.
- Received December 7, 2015.
- Revision received April 9, 2016.
- Accepted May 13, 2016.
- Copyright ©2016, American Association for Cancer Research.