Abstract 1528: 6B5, an anti-human B7-H3 therapeutic antibody that enhances antibody-dependent cellular cytotoxicity and inhibits tumor growth in B7-H3-humanized mice

Abstract

Abstract B7-H3 (CD276) is a type I transmembrane protein belonging to the B7 family of immune-regulatory ligands. Initially reported as a costimulatory signal of human T cells, increasing evidence suggests that it may also have coinhibitory function. TLT-2 has been identified as a potential cognate receptor for B7-H3, but others may exist. Overexpression of B7-H3 protein is found in a variety of human cancers, including lung adenocarcinomas, neuroblastomas, gliomas, and pancreatic tumors—and is associated with poor prognosis and survival. While B7-H3 can promote T cell activation and anti-tumor responses in the context of CD3 stimulation, its coinhibitory function inhibits T and NK cell activity in the tumor microenvironment. We generated 6B5, a fully human B7-H3 monoclonal antibody, from murine B7-H3 knock-out RenMab™ mice, which contain the full human immunoglobulin variable domain. 6B5 is cross-reactive with rodent and cynomolgus monkey B7-H3. It displays higher affinity for tumor cell lines than Enoblituzumab. 6B5 has no staining on normal human tissues. In vitro antibody-dependent cellular cytotoxicity (ADCC) against H520 squamous cell carcinoma cells was potentiated by 6B5 relative to Enoblituzumab and, critically, did not exhibit the hook effect at high dosage. In vivo efficacy of 6B5 in humanized B7-H3 mice bearing murine EL4 lymphomas was comparable to Enoblituzumab. ADCC enhancement in vivo was comparable to afucosylation or five-point mutations. Epitope mapping revealed non-overlapping B7-H3 binding epitopes of 6B5 and Enoblituzumab. Taken together, these data suggest that 6B5 is a promising therapeutic anti-human B7-H3 IgG monoclonal antibody that may find clinical application in a range of cancers, including current refractory types. Citation Format: Yunyun Chen, Jiangmei Li, Yanan Guo, Wenqi Hu, Ting Mao, Li Hui, W. Frank An, Yi Yang, Feng Li. 6B5, an anti-human B7-H3 therapeutic antibody that enhances antibody-dependent cellular cytotoxicity and inhibits tumor growth in B7-H3-humanized mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1528.