Abstract 1343: BSI-111, a highly selective anti-CD16a monoclonal antibody with potent agonist activity for building a NK cell engager platform

Abstract Background: Natural killer cells (NK) are innate lymphocytes endowed with the ability to recognize and kill cancer cells. CD16a, a well-characterized activating receptor predominantly expressed on NK cells, is a low-affinity receptor for the IgG Fc domain and is crucial for stimulating NK cell-mediated tumor cell killing. Unlike CD16a, CD16b is mainly expressed on granulocytes as a GPI-anchored receptor and is not involved in the lysis of tumor cells although CD16a and CD16b share 97% sequence identity in their extracellular domains. Due to the high homology of extracellular domains of CD16a and CD16b, it is extremely challenging to develop CD16a-specific agonistic antibodies without binding CD16b+ granulocytes, the most abundant subset in leukocytes. Here we report the development of an anti-CD16a-specific monoclonal antibody with potent NK cell activation. Experimental procedures: Humanized mice were immunized with recombinant CD16a-ECD-Fc. The Biosion proprietary H3 (High-throughput, High-content and High-efficiency) antibody screening platform was used to identify an anti-CD16a monoclonal antibody lead candidate - BSI-111. The target binding specificity, binding activity, and affinity of BSI-111 were evaluated by protein-based ELISA, cell-based FACS and Biacore-based SPR. A cell-based agonist reporter assay and a primary NK cell activation assay were used to evaluate the bioactivity of BSI-111. Summary: BSI-111 is a fully human monoclonal antibody with the following critical properties: (1) specifically binds to CD16a without recognizing CD16b; (2) binds the two allelic variants of CD16A - 158F and 158V with similar high affinities; (3) shows cross-reactivity to cynomolgus CD16a; (4) can significantly activate NFAT signaling in a cell-based reporter assay; (5) exhibits strong activity on activating primary NK cells; and (6) has potentially longer half-life and silenced Fc-effector function through Fc-engineering. Conclusion: BSI-111 demonstrates great biophysical properties and functional characteristics, supporting the development of anti-CD16a-based NK cell engagers for potential benefit of cancer patients. Citation Format: Jinyu Liu, Wenwen Dai, Hongyan Li, Xiaodong F. Liu, Jun Li, Shukai Xia, Qun Lyu, Hugh M. Davis, Mingjiu Chen, Zeyu Peng. BSI-111, a highly selective anti-CD16a monoclonal antibody with potent agonist activity for building a NK cell engager platform abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1343.