Immune checkpoint inhibitors, i.e., PD1 and CTLA4 antibody therapeutics, have led to long-term survival in many late-stage solid tumor patients. Despite this revolutionary clinical impact, the overall response rate is still low. One major roadblock is that compensatory immune inhibitory pathways were turned on to protect tumor cells from being attacked by T cells. T cell immunoglobulin- and mucin domain-containing molecule 3 (Tim-3) is a type I transmembrane protein expressed in T cells, monocytes, macrophages, and dendritic cells. PD-1 and Tim-3 coexpression is often associated with an exhausted phenotype of tumor-infiltrating lymphocyte (TIL) in various tumor types. TIM-3 expression has been reported as a compensatory mechanism in the PD1 nonresponsive patients. Simultaneously targeting PD1 and TIM3 is now being actively tested in clinical trials. However, we still do not have an animal model that can efficiently evaluate the efficacy of therapeutic TIM3 antibodies or combinations. Here we report generation of a human TIM3 knock-in C57BL/6 mouse model, in which we replaced mouse exon 2-5 of HAVCR2 gene with human counterparts. The engineered knock-in mice express a chimeric TIM3 where its extracellular and transmembrane domains are human sequence, while the signal peptide and intracellular domain are kept intact. We confirmed that homozygous knock-in mice only express this chimeric TIM3, recognizable by human TIM3 antibody in NK cells, macrophages, and stimulated T cells. In an efficacy study, we inoculated the TIM3 knock-in mice with MC38 syngeneic tumor cells. Treating the mice with 5 mg/kg of human TIM3 antibody resulted in modest tumor growth inhibition (TGI), while in combination with anti-mouse PD1 antibody, the TGI improved to 62% following 2 weeks of treatment. We are now breeding the human PD1 and human TIM3 double knock-in mice to test the combinatory therapeutic antibodies. We have also developed human PD-L1 expressing MC38 cells, so that when inoculated in human TIM3 knock-in mice, PD-L1 and TIM3 therapeutic combination can be evaluated.

Citation Format: Lei Zheng, Xuesong Huang, Wenyi Ouyang, Gang Chen, Annie Xiaoyu An, Xin Dong, Jay Liu, Jean Pierre Wery, Qian Shi, Davy Xuesong Ouyang. Generation of human TIM3 knock-in mice for preclinical efficacy assessment of therapeutic antibodies [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A203.