Abstract 2875: Development of a new tumor-bearing humanized mouse model to evaluate the efficacy and toxicity of bispecific T cell engagers
Authors: Yang Guoxiang , Yao Li-Chin , Brehm Michael A. , Greiner Dale L. , Shultz Leonard D. , Cai Danying , Cheng MIngshan , Keck James G. 
Published: June 2022

Abstract
Background: T cell-based immunotherapies, especially the bispecific T cell engager (BiTE), which recruit T cells to tumor cells, have been developed rapidly for treatment of malignancies. However, the wide application of BiTE therapies is limited by accompanying severe adverse effects such as cytokine release syndrome (CRS). Since human cancer cells are not incorporated in the CRS evaluation, currently used in vivo animal models and in vitro human immune cell activation assays do not reliably evaluate the induction of CRS by immune drugs that is seen in BiTE treated cancer patients. In addition, the differences between human and mouse immune systems hamper the development of new immune-oncology therapeutic drugs. Thus, establishing a predictive in vivo animal model that can screen both efficacy of cancer therapy and risk of developing CRS is critical for improving the safety of immune drug development for treatment of cancer patients.
Method: Humanized mice were developed in NSG-MHC class I/II double knock out (DKO) mouse recipients following reconstitution with human peripheral blood mononuclear cells. The MDA-MB-231/Luciferase-2A-GFP stable breast cancer cell line (MDA), which expressed epidermal growth factor receptor (EGFR), were implanted in mice 5 days after PBMC engraftment. Following EGFRxCD3 BiTE treatment whole-body tumor burden was quantified by an in vivo imaging system. To evaluate the CRS levels in response to BiTE therapy, cytokine levels were analyzed by BD cytometric bead array. Clinical observations, CRS scores, body weight changes and human immune cell activation were also monitored for CRS assessment.
Results: PBMC humanized models were successfully established with breast cancer cell engraftment. After treatment with EGFRxCD3 BiTE, the mice exhibited elevated serum levels of human IFNgamma, TNF-a, IL-6, IL-10, IL-2 and IL-4 compared to a vehicle control group. This cytokine production was dose-dependent and was associated with an increase of toxic mouse clinical evaluation score. In contrast, there was no significant inflammatory cytokine production in PBMC humanized mice without MDA cell implantation, suggesting T cell activation by BiTE followed binding to the cancer cells. BiTE treatment for 2-4 days significantly suppressed tumor growth in lung as measured by luciferin imaging. With serial doses of BiTE treatment, we observed a dose-dependent inhibition of tumor growth.
Conclusion: We developed a novel in vivo PBMC humanized mouse model bearing human tumor cells that can be used to determine the optimal dose of BiTE for inhibition of tumor growth with low toxicity risk. This model provides a growth environment similar to that of patients and has important application values in simultaneously evaluating the efficacy and safety of any T cell-based immunotherapies including BiTE to define optimal approaches for clinical cancer treatment.
Citation Format: Guoxiang Yang, Li-Chin Yao, Michael A. Brehm, Dale L. Greiner, Leonard D. Shultz, Danying Cai, MIngshan Cheng, James G. Keck. Development of a new tumor-bearing humanized mouse model to evaluate the efficacy and toxicity of bispecific T cell engagers [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 2875.