Novel tetravalent bispecific T-cell engaging antibodies for cancer immunotherapy.

Abstract

e12513 Background: Current immunotherapy involves redirection of T cells against tumor either by chimeric antigen receptors (CAR-T) or bispecific T-cell engagers (BiTEs). These T cell-engaging technologies have been enabled by engineering single-chain variable fragment (scFv). Most BiTEs are designed as heterodimers, with monovalent binding to tumor cell surface antigens and to CD3+ T cells. Here, we describe a novel tetravalent bispecific (TetraBi) platform: a tumor associated antigen specific, T-cell engaging antibody that provides significant advantages over traditional BiTEs. Specifically, we showcase three unique TetraBi antibodies targeted for various cancers. Methods: ABP-100 was engineered by fusing CD3-binding scFv to the c-terminus of anti-HER2 IgG1 light chain, resulting in two binding sites each for HER2 and CD3. In preclinical studies, ABP-100 was compared with a clinical-stage heterodimeric antibody that is monovalent for HER2 and CD3. We also built TetraBi for anti-Glypican 3 (GPC3, ABP-110) and Claudin 18.2 (CLDN18.2, ABP-150) for gastric cancer therapy. Results: We observed bivalent binding to the tumor antigens (HER2, GPC3, CLDN18.2) on tumor cells like the monoclonal antibodies do. Interestingly, the CD3-binding domains in our TetraBi format showed functionally monovalent binding to CD3. ABP-100 displayed comparable cytokine release to the heterodimer molecule both in vitro and in vivo. In HER2+ cancer models, ABP-100 showed highly potent antitumor activity, resulting in complete responses in tumor bearing mice at doses as low as 0.1 mg/kg with no evidence of tumor relapse. ABP110 and ABP-150 also demonstrated potent cancer cell killing in vitro. Conclusions: This novel TetraBi antibody format enables concurrent bivalent and monovalent co-engagement of distinct target antigens in tumor microenvironment with promising therapeutic implications. Furthermore, it provides a potentially larger therapeutic index than more traditional bispecific formats that feature monovalent recognition of tumor antigens.