Abstract 1338: Humanized mouse model for in vivo evaluation of bispecific antibody efficacy

Abstract

Abstract Bispecific antibodies have shown several promising advantages over monoclonal antibodies and are emerging as one of growing cancer immunotherapies. Preclinical in vivo models to assess efficacy associated with immune cell engagement are needed. Here we evaluated an EGFR bispecific T cell engager (EGFRXCD3 BiTE) using xenograft models in humanized NSG™ (NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ) mice that have been engrafted with human CD34+ HSC and have human T cells in circulation. Three EGFR+ tumor models were used in this report including LG1202 lung PDX and two triple negative breast cancer cell lines MDA-MB-231 with a high EGFR expression level and MDA-MB-453 with a low EGFR expression. Interestingly we found that all three models were resistant to EGFR monoclonal antibody drug cetuximab despite the expression of EGFR but responded to EGFRXCD3 BiTE. BiTE-induced T cell activation was evident through the analysis of tumor infiltrated lymphocytes by flow cytometry at the end of the study. BiTE treatment for 3 weeks effectively reduced the LG1202 tumor growth whereas the effect of cetuximab on the tumor growth was minimal. In the BiTE-treated group, CD3+ T cell percentage increased as compared to the vehicle group, and both CD4+ and CD8+ T cell subsets showed an increased frequency of CD69+ cells. We also observed elevated levels of human cytokines IFN-γ, IL-6, IL-2, and IL-10 in circulation 4 h after animals received the first BiTE dose. We evaluated the dose response of BiTE treatments on MDA-MB-231 model with a high EGFR expression. Low dose BiTE reduced tumor growth whereas high dose BiTE effectively prevented or even regressed some tumor growth. Flow analysis showed that tumor CD3+ T cell frequency remained similar to the vehicle group but CD8+ T frequency increased after high dose BiTE. High CD69+CD8+ T cell frequency was found in the vehicle group and the percentage further increased after high dose BiTE. For the low EGFR-expressing MDA-MB-453 model, BiTE treatment for 4 weeks also effectively reduced the tumor growth. In comparison, while cetuximab treatment decreased EGFR expression on tumor cells, it did not reduce the tumor growth. Flow analysis showed that BiTE-treated group had increased T cell infiltration into the tumors when compared to the PBS and cetuximab groups. The frequency and cell number of CD25+ and CD69+ CD4+ T and CD8+ T cells in the tumor increased after BiTE treatment. Together, these data support our humanized mouse model to be used to validate T-cell dependent bispecific antibody efficacy. Citation Format: Li-Chin Yao, James G. Keck, Danying cai. Humanized mouse model for in vivo evaluation of bispecific antibody efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1338.