（チャールズ・リバー）ヒト特異的免疫チェックポイント阻害剤の評価に向けた、革新的な生体内前臨床ヒト化モデル

要旨

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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