T-cell redirecting therapy has taken a prominent area in immuno-oncology. T cells driven by a tumor-specific antigen, traffic into the tumor and initiate tumor killing. However, this is often hampered by inhibitory factors in the tumor microenvironment. In recent years, researchers have been actively developing T-cell redirecting bispecific antibodies, which binds to a specific tumor associated antigen (TAA) on tumor cells and CD3 (usually epsilon chain, CD3E) on T cells. This physically links the tumor cell to the T-cell which leads to MHC-independent recognition and killing of cells carrying the TAA. Several CD3 recruiting bispecific antibodies that have been approved are now in clinical trials and demonstrate promising efficacy. However, research on new therapeutic T-cell redirecting antibodies is often hampered by a lack of proper in vivo models, due to the absence of cross-reactivity with mouse CD3ε. We have now built a human CD3E BAC transgenic model in BALB/c background to address this issue. These transgenic mice express both human- and mouse CD3ε in more than 80% of the T cells. Unlike previously developed transgenic lines, where early T lymphocyte and natural killer cell development were blocked in mice with high copy numbers of the human CD3ε gene, our model is phenotypically normal with levels of T , B , and NK cells comparable to those in wild-type BALB/c mice. In an ex vivo T-cell stimulation assay, spleen-derived T cells could be activated by either anti-human CD3 antibody (OKT3) or anti-mouse CD3 antibody (145-2C11), indicated by significantly elevated CD25+/CD69+ population, as well as IL-2 and IFNγ release. In an efficacy assay, we inoculated syngeneic mouse CD20-expressing A20 lymphoma cells into the transgenic mice and treated with mCD20xmCD3 or mCD20xhCD3 bispecific antibodies, containing a human- or mouse CD3ε-specific CD3 arm, respectively. We found complete depletion of peripheral B cells 48 hours after dosing of either bispecific antibody. Treatment also induced 33% and 39% tumor growth inhibition at day 10, following 3 doses of 1 mg/kg mCD20xhCD3 and mCD20xmCD3 bispecific antibody, respectively. Taken together, our human CD3ε transgenic mice offer a novel model to assess the preclinical in vivo efficacy of human CD3-T-cell redirecting therapeutics.

Citation Format: Mengmeng Yang, Mingkun Zhang, Sandra Verploegen, Patrick Engelberts, Yuxi Zhang, Lei Zheng, Keyi Zhu, Annie Xiaoyu An, Cunxiang Ju, Jing Zhao, Xiang Gao, Qian Shi, Davy Xuesong Ouyang. Establishment of a human CD3ε transgenic mouse model to assess anti-tumor efficacy of human T-cell-redirecting bispecific antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5669.