Targeting CD137 to enhance the antitumor efficacy of cetuximab by stimulation of innate and adaptive immunity.

Abstract

3015 Background: Cetuximab therapy results in beneficial, yet limited, clinical improvement for patients with KRAS wildtype (WT) colorectal (CRC) and head and neck (HN) cancer. The efficacy of cetuximab, an IgG1 monoclonal antibody against EGFR, is due in part to antibody-dependent cell-mediated cytotoxicity (ADCC) by natural killer (NK) cells. CD137 is a costimulatory molecule expressed following activation on NK and memory, antigen-specific, CD8 T cells. Methods: We investigated the hypothesis that the combination of cetuximab with anti-CD137 mAb will enhance innate and adaptive immunity, thereby improving cetuximab’s anti-tumor efficacy in preclinical models and a prospective trial, NCT01114256. Results: NK cells increased their expression of CD137 by a factor of 30-40 when exposed to cetuximab-coated, EGFR-expressing HN and CRC cell lines. An agonistic anti-CD137 mAb enhanced NK cell degranulation and cytotoxicity 2-fold (~45 to 90% tumor lysis assayed by chromium release). The combination of cetuximab and anti-CD137 mAbs was synergistic in a syngeneic, human-EGFR-transfected murine tumor leading to complete tumor resolution and prolonged survival. NK cell depletion, significantly, and CD8 T cell depletion, partly, abrogated the anti-tumor efficacy of this combination. A series of HN and both KRAS WT and mutant CRC xenotransplant models demonstrated synergy with cetuximab and anti-CD137 mAbs. In our clinical trial, 54 patients with HN cancer receiving cetuximab therapy, circulating and intratumoral NK cells upregulated CD137 with amplitude influenced by duration post-cetuximab and host FcyRIIIa polymorphism. Interestingly, in 10 HLA-A2+ patients, following cetuximab, an increase in EGFR-specific, CD137-expressing, CD8 T cells directly correlated with the percent increase in CD137-expressing NK cells. Conclusions: Our results demonstrate the synergy of combining an agonistic mAb, anti-CD137, augmenting ADCC and T cell memory following a tumor-targeting mAb, cetuximab, in HN and KRAS mutant and WT CRC cancer. These results support a novel, sequential antibody approach by targeting first the tumor and then the host innate and adaptive immune system. Clinical trial information: NCT01114256.