Superior T Cell Activity of a Membrane-Proximal Binding Antibody when Targeting Glypican-3 with an Antibody-Coupled T-cell Receptor (ACTR) Armed T Cell

Abstract Glypican-3 (GPC3) is a GPI-anchored member of the heparan sulfate proteoglycan family. GPC3 is an oncofetal antigen expressed transiently during fetal development with re-expression during malignant transformation. GPC3 is an ideal tumor target as expression has been found in numerous epithelial malignancies, with highest expression in hepatocellular carcinoma (HCC) and non-small cell lung carcinoma (NSCLC), and normal tissue expression is highly restricted (Baumhoer D., Am J Clin Pathol, 2008.). Adoptive T-cell therapy with single-chain variable fragment (scFv)-derived chimeric antigen receptors (CARs) has transformed cancer therapy, but the broad applicability of this approach has been limited in part by safety concerns due the constitutive expression of a biologically active targeting receptor. The Antibody-Coupled T-cell Receptor (ACTR) platform is a universal, engineered T-cell therapy designed to engage the Fc domain of therapeutic antibodies opsonized to tumor cells to mediate anti-tumor activity. ACTR activity is therefore both regulatable and flexible, providing enhanced therapeutic control and improved safety of the T cell therapy. Using both HCC and NSCLC tumor cell lines, we tested a panel of wild-type and afucosylated antibodies with similar binding affinities that bound to regions spanning the GPC3 protein across unique epitopes. We found that for GPC3 targeting antibodies, the greatest activity in a Jurkat-NFAT reporter assay was observed for the afucosylated antibody that bound GPC3 most proximal to the membrane. Further, the antibody that bound membrane proximal also had the most potent activity in primary ACTR T cell cytotoxicity and cytokine release assays. The physical distance between T cells and tumor targets has been previously determined to impact T cell activation for both peptide-MHC and CAR-T interactions. Similarly, our results demonstrate a potential relationship between spatial distance of tumor targets and T cells in determining the activity ACTR transduced T cells when targeting GPC3. Our data demonstrate that ACTR T cell activity is antibody-specific and dose-titratable, highlighting both efficacy and improved safety of the ACTR T cell platform when targeting GPC3+ solid tumor malignancies. Citation Format: Greg Motz, John Shin, Kathleen Whiteman, Birgit Schultes, Tapasya Pai, Lori Westendorf, Seth Ettenberg, Travis Biechele, Django Sussman, Heather Huet. Superior T cell activity of a membrane-proximal binding antibody when targeting Glypican-3 with an antibody-coupled T-cell receptor (ACTR) armed T cell [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3762. doi:10.1158/1538-7445.AM2017-3762