Abstract 1831: Affinity tuned XmAb®2+1 GPC3 x CD3 bispecific antibodies demonstrate selective activity in liver cancer models

Abstract

Abstract Bispecific T cell engagers simultaneously bind CD3 on T cells and tumor-associated antigens to promote T cell-mediated killing of tumor cells. These agents provide synthetic immunity by expanding, activating, and redirecting T cells against a target of interest. While targeting lineage-restricted antigens such as CD19 or CD20 have found clinical success in hematopoietic cancers, targeting solid tumors requires high expressing tumor associated antigens (TAAs) with minimal normal tissue expression. Glypican 3 (GPC3), a lipid-anchored cell surface protein, is over-expressed in the majority of hepatocellular carcinoma (HCC) and a smaller subset of lung squamous cell carcinoma. It is considered an ideal target because its expression is not detected in adult tissues, and its function can promote tumor growth through the Wnt/beta-catenin pathway. Although GPC3 demonstrates good differential expression, bispecific T cell engagers are powerful immunomodulatory agents and careful tuning can improve the therapeutic window on all targets. Building upon the XmAb® heterodimeric Fc platform, we generated bispecific antibodies in an XmAb 2+1 Fab2-scFv-Fc format that are bivalent for GPC3 and monovalent for CD3. Reducing the affinity of GPC3 encouraged avid binding and strong killing activity only on high GPC3 expressing cell lines while minimizing reactivity on low expressing cell lines. We found modulating the CD3 affinity, either directly through mutation or indirectly by the molecular format, contributes to the selectivity of the bispecific antibodies. To ensure biologically valid antigen densities were being considered, IHC was conducted on paraffin embedded arrays of tumor tissue, normal tissue, and cell lines. Upon matching the staining intensity between the three sample types, we identified cell lines with corresponding GPC3 antigen density that could serve as proxies of tumor and normal tissue. In vitro T cell-dependent cellular cytotoxicity (TDCC) assays on the relevant cell lines confirmed selective potency on high versus low expressing cells. Citation Format: Alex Nisthal, Nargess Hassanzadeh-Kiabi, Kendra N. Avery, Rumana Rashid, Juan E. Diaz, Umesh S. Muchhal, Seung Y. Chu, Gregory L. Moore, Katrina Bykova, John R. Desjarlais. Affinity tuned XmAb®2+1 GPC3 x CD3 bispecific antibodies demonstrate selective activity in liver cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1831.