Background. Blockage of immune checkpoints, e.g. by anti-PD1 antibody, becomes an important new cancer therapy1. Experimental models are important to evaluate new investigational therapy or new combination strategy. Syngeneic mouse tumor models have been widely utilized as an experimental model for testing surrogate immune-oncology (I/O) therapy by using its competent mouse immunity2, but cannot be used for testing human biologic therapeutics, due to the species specificity. The direct replacing mouse therapeutic target by human counterpart in mouse while maintaining the normal mouse immune-functions could be a potential practical preclinical approach to evaluate human biologic therapeutics in vivo.

Methods. We have engineered a chimeric human/mouse PD1 gene (h/mPD1) composed of human exome 2&3 and mouse exome 1&4. We expressed the recombinant proteins and tested their bindings to their binding partner of PDL1 of both mouse and human origins, and also anti-human PD1 antibody. We knock-in the recombinant gene into C57Bl/6 mouse to create homozygous HuGEMM-h/mPD1 mouse, which is tested for growth of MC38 syngeneic mouse cell line tumor graft and for the growth inhibition by anti-human PDL1 antibody.

Results. Our data demonstrated that chimeric protein h/mPD1 can interchangeably interact with mPDL1 or hPDL1 efficiently as efficiently as mouse PD1, and it also recognizes anti-human PD1 antibody as expected. The binding of anti-human PD1 antibody blocks its binding to mouse or human PDL1. The knock-in mice express the chimeric gene in the T-cells of the engineered mice both in vivo and ex vivo, however at significantly lower levels than mouse PD1 in the wild type C57BL/6 mice (1/10) under induction. When syngeneic MC38 cell line was subcutaneously engrafted in HuGEMM-h/mPD1 mice, the tumor were found to grow significantly slower with increased T-cell infiltration, as compared to those in the wild type mice. MC38 tumor did not respond to anti-human PD1 antibody well either. These observations can apparently be attributed to the low level PD1 and the associated high autoimmunity that also inhibits tumor growth. Interestingly, a specific condition can be artificially created to enhance MC38 tumor growth in the chimeric mice, likely contributed by the enhanced h/mPD1 expression. The enhanced tumor growth seems to also be suppressible, at least partially, by anti-human PD1 antibody as shown in our preliminary study. Currently, we are re-engineering our chimeric gene (version 2) in order to increase their expression to the wild type gene level, so to create a model for more optimal drug evaluation. In the meantime, we are also engineering HuGEMM-hu-CKPT (e.g. CTLA4 PDL-1, OX40, 4-1BB, etc.) for evaluating other checkpoint inhibitors.

Conclusions. Our data suggests the conditioned version 1-HuGEMM-h/mPD1 mouse can be explored to evaluate anti-human antibody.

References

1. Pardoll, D.M. The blockade of immune checkpoints in cancer immunotherapy. Nature reviews. Cancer 12, 252-264 (2012).

2. Allard, B., Pommey, S., Smyth, M.J. & Stagg, J. Targeting CD73 enhances the antitumor activity of anti-PD-1 and anti-CTLA-4 mAbs. Clinical cancer research : an official journal of the American Association for Cancer Research 19, 5626-5635 (2013).

Citation Format: Zhun Wang, Bin Cai, GANG Chen, Jinping Liu, Xiaoyu An, Zhengsheng Wang, Davy Ouyang, Jean-Pierre Wery, Jay Liu, Xin Dong, Henry Li. HuGEMM-h/mPD1 mouse models for assessing anti-human PD1 therapeutics. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A11.