近期免疫检查点阻滞（ICB）的进展提高了失配修复缺陷和微卫星不稳定型结肠癌（dMMR/MSI-H CRC）患者的预后。然而，PD-1阻滞在早期进展性疾病中面临挑战。我们旨在利用体内模型了解ICB耐药的早期事件。我们将MC38结肠癌细胞皮下移植到C57BL / 6小鼠中，静脉注射抗PD-1抗体，然后从复发肿瘤中分离出ICB耐药亚克隆细胞。比较基因表达分析发现，在ICB耐药细胞中显著下调的七个基因。将MC38细胞的每个候选基因敲除对C57BL/6小鼠进行肿瘤形成试验，并通过基因组学分析候选基因的表达与接受免疫治疗的癌症患者结果之间的关系，确定Rtp4（一个受干扰素刺激的基因和G蛋白偶联受体的伴侣蛋白）是参与ICB耐药性的基因。移植瘤组织的免疫组织化学分析表明，在Rtp4-KO MC38细胞中，抗PD-1抗体未能招募T淋巴细胞。小鼠和人体RTP4表达可以通过组蛋白H3赖氨酸9（H3K9）三甲基化被沉默，并且公共转录组数据表明，大多数但不是所有dMMR/MSI-H CRC的RTP4表达水平很高。我们澄清了RTP4可以被组蛋白H3K9甲基化沉默为ICB耐药的早期事件。RTP4表达可作为预测ICB反应的有希望的生物标志物，而表观遗传药物与免疫检查点抑制剂的结合可能对dMMR/MSI-H CRC产生协同效应。©2023年。日本胃肠病学会。

Recent advances in immune checkpoint blockade (ICB) have improved patient prognosis in mismatch repair-deficient and microsatellite instability-high colorectal cancer (dMMR/MSI-H CRC); however, PD-1 blockade has faced a challenge in early progressive disease. We aimed to understand the early event in ICB resistance using an in vivo model.We subcutaneously transplanted the MC38 colon cancer cells into C57BL/6 mice, intraperitoneally injected anti-PD-1 antibody and then isolated ICB-resistant subclones from the recurrent tumors.Comparative gene expression analysis discovered seven genes significantly downregulated in the ICB-resistant cells. Tumorigenicity assay of the MC38 cells knocked out each of the seven candidate genes into C57BL/6 mice treated with anti-PD-1 antibody and bioinformatics analysis of the relationship between the expression of the seven candidate genes and the outcome of cancer patients receiving immunotherapy identified Rtp4, an interferon-stimulated gene and a chaperon protein of G protein-coupled receptors, as a gene involved in ICB resistance. Immunohistochemical analysis of transplanted tumor tissues demonstrated that anti-PD-1 antibody failed to recruit T lymphocytes in the Rtp4-KO MC38 cells. Mouse and human RTP4 expression could be silenced via histone H3 lysine 9 (H3K9) trimethylation, and public transcriptome data indicated the high expression level of RTP4 in most but not all of dMMR/MSI-H CRC.We clarified that RTP4 could be silenced by histone H3K9 methylation as the early event of ICB resistance. RTP4 expression could be a promising biomarker for predicting ICB response, and the combination of epigenetic drugs and immune checkpoint inhibitors might exhibit synergistic effects on dMMR/MSI-H CRC.© 2023. Japanese Society of Gastroenterology.