熟练的错配修复或微卫星稳定（pMMR/MSS）结直肠癌（CRC）数量远远少于缺乏错配修复或微卫星不稳定高（dMMR/MSI-H）肿瘤，并且对免疫检查点抑制剂（ICIs）没有反应。在本研究中，我们报告了pMMR/MSS CRC和dMMR/MSI-H CRC中ASCL2的两种不同表达模式。ASCL2在pMMR/MSS CRC中过度表达，保持干细胞特性，并伴随着肿瘤浸润淋巴细胞（TILs）密度较低，低于dMMR/MSI CRC中的TILs密度。此外，抗PD-L1抗体的联合给药促进了T细胞浸润，并触发了强烈的抗肿瘤免疫和肿瘤退缩现象，在MC38/shASCL2小鼠CRC模型中实现。此外，ASCL2的过表达与增加的TGFB水平相关，促进了局部癌相关成纤维细胞（CAFs）的激活，诱导了一个免疫排斥型的微环境。与之一致，肠道中特异性缺失Ascl2（Villin-Cre+，Ascl2 flox/flox，命名为Ascl2 CKO）的小鼠显示出较少活化的CAFs和较高比例的浸润CD8+ T细胞；我们进一步对Ascl2 CKO与ApcMin/+模型进行交叉，发现肠道中Ascl2缺失表达与良好预后相关的免疫浸润环境有关。综上所述，我们的发现表明ASCL2通过转录活化TGFB来激活CAFs，导致免疫排斥型微环境。靶向ASCL2与ICIs的联合治疗可能为MSS CRC提供治疗机会。© 2023. 作者。

Proficient mismatch repair or microsatellite stable (pMMR/MSS) colorectal cancers (CRCs) are vastly outnumbered by deficient mismatch repair or microsatellite instability-high (dMMR/MSI-H) tumors and lack a response to immune checkpoint inhibitors (ICIs). In this study, we reported two distinct expression patterns of ASCL2 in pMMR/MSS and dMMR/MSI-H CRCs. ASCL2 is overexpressed in pMMR/MSS CRCs and maintains a stemness phenotype, accompanied by a lower density of tumor-infiltrating lymphocytes (TILs) than those in dMMR/MSI CRCs. In addition, coadministration of anti-PD-L1 antibodies facilitated T cell infiltration and provoked strong antitumor immunity and tumor regression in the MC38/shASCL2 mouse CRC model. Furthermore, overexpression of ASCL2 was associated with increased TGFB levels, which stimulate local Cancer-associated fibroblasts (CAFs) activation, inducing an immune-excluded microenvironment. Consistently, mice with deletion of Ascl2 specifically in the intestine (Villin-Cre+, Ascl2 flox/flox, named Ascl2 CKO) revealed fewer activated CAFs and higher proportions of infiltrating CD8+ T cells; We further intercrossed Ascl2 CKO with ApcMin/+ model suggesting that Ascl2-deficient expression in intestinal represented an immune infiltrating environment associated with a good prognosis. Together, our findings indicated ASCL2 induces an immune excluded microenvironment by activating CAFs through transcriptionally activating TGFB, and targeting ASCL2 combined with ICIs could present a therapeutic opportunity for MSS CRCs.© 2023. The Author(s).