(Charles River) Novel in vivo preclinical humanized models for the evaluation of human specific immune checkpoint inhibitors.

Abstract

In the last few years, there has been an increasing demand for suitable pre-clinical mouse models for evaluating the efficacy of checkpoint inhibition-based cancer immunotherapies. During tumor progression, immune cells can become unresponsive and evade immune surveillance upon chronic activation and expression of the programmed cell death protein-1 (PD-1) the ligand PD-L1 on tumor cells or expression of the T lymphocyte associated antigen 4 (CTLA4) in T-cells cells resulting in tumor immune-tolerance. We have previously demonstrated that murine anti-PD-1, anti-PD-L1 and CTLA-4 blockade can effectively enhance immune normalization and re-activate the antitumor response against multiple syngeneic tumor models. While these models proved instrumental for evaluating murine immune-checkpoint inhibitors (ICI), there is a clear need for additional mouse models to evaluate the efficacy of ICI specific for human targets. To address this need, we describe the development of humanized PD-1 and CTLA-4 knock-in (KI) mouse models. The main advantage of these models is that human PD-1 or CTLA-4 proteins are expressed in the context of a fully functional immune system. To validate these models we evaluated the response to pembrolizumab or ipilimumab in a colorectal carcinoma and a glioblastoma preclinical tumor models. We observed significant tumor growth inhibition and growth delay in the MC38 tumor model with either monotherapy, but not when treated with the murine counterparts: anti-PD-1 (clone RPM1-14) or CTLA-4 (clone 9H10). To extend our validation studies to other tumor models, we implanted GL261 glioblastoma orthotopically in the brain of PD-1 KI mice and achieved a significant increased life span in the group treated with pembrolizumab compared to both the control group and the group treated with murine anti-PD-1 antibody. Furthermore, we found that pembrolizumab and ipilimumab therapy results in enhanced effector functions of CD4+and CD8+ T cells associated with increased expression of Granzyme B. In summary, the results shown here underscore the value of resourcing to humanized knock-in (KI) mouse models as tools to evaluate human specific immune-checkpoint based therapeutics alone and in combination with other agents.

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