Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA.
Department of Biostatistics and Bioinformatics, Roswell Park Cancer Institute, Buffalo, New York, USA.
J Immunother Cancer. 2021 Jan;9(1). doi: 10.1136/jitc-2020-002115.
Immune checkpoint inhibitors (ICIs) have had a profound impact on the treatment of many tumors; however, their effectiveness against triple-negative breast cancers (TNBCs) has been limited. One factor limiting responsiveness of TNBCs to ICIs is a lack of functional tumor-infiltrating lymphocytes (TILs) in 'non-inflamed' or 'cold' tumor immune microenvironments (TIMEs), although by unknown mechanisms. Targeting MUC1-C in a mouse transgenic TNBC tumor model increases cytotoxic tumor-infiltrating CD8+ T cells (CTLs), supporting a role for MUC1-C in immune evasion. The basis for these findings and whether they extend to human TNBCs are not known.
Human TNBC cells silenced for MUC1-C using short hairpin RNAs (shRNAs) were analyzed for the effects of MUC1-C on global transcriptional profiles. Differential expression and rank order analysis was used for gene set enrichment analysis (GSEA). Gene expression was confirmed by quantitative reverse-transcription PCR and immunoblotting. The The Cancer Genome Atlas Breast Invasive Carcinoma (TCGA-BRCA) and Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) datasets were analyzed for effects of MUC1 on GSEA, cell-type enrichment, and tumor immune dysfunction and exclusion. Single-cell scRNA-seq datasets of TNBC samples were analyzed for normalized expression associations between MUC1 and selected genes within tumor cells.
Our results demonstrate that MUC1-C is a master regulator of the TNBC transcriptome and that MUC1-C-induced gene expression is driven by STAT1 and IRF1. We found that MUC1-C activates the inflammatory interferon (IFN)-γ-driven JAK1→STAT1→IRF1 pathway and induces the IDO1 and COX2/PTGS2 effectors, which play key roles in immunosuppression. Involvement of MUC1-C in activating the immunosuppressive IFN-γ pathway was extended by analysis of human bulk and scRNA-seq datasets. We further demonstrate that MUC1 associates with the depletion and dysfunction of CD8+ T cells in the TNBC TIME.
These findings demonstrate that MUC1-C integrates activation of the immunosuppressive IFN-γ pathway with depletion of TILs in the TNBC TIME and provide support for MUC1-C as a potential target for improving TNBC treatment alone and in combination with ICIs. Of translational significance, MUC1-C is a druggable target with chimeric antigen receptor (CAR) T cells, antibody-drug conjugates (ADCs) and a functional inhibitor that are under clinical development.
免疫检查点抑制剂（ICIs）对许多肿瘤的治疗产生了深远影响；然而，它们对三阴性乳腺癌（TNBC）的疗效有限。限制 TNBC 对 ICI 反应的一个因素是缺乏功能肿瘤浸润淋巴细胞（TILs）在“非炎症”或“冷”肿瘤免疫微环境（TIME）中，尽管其机制尚不清楚。在小鼠转基因 TNBC 肿瘤模型中靶向 MUC1-C 会增加细胞毒性肿瘤浸润 CD8+T 细胞（CTL），支持 MUC1-C 在免疫逃逸中的作用。这些发现的基础以及它们是否扩展到人类 TNBC 尚不清楚。
使用短发夹 RNA（shRNA）沉默 MUC1-C 的人类 TNBC 细胞被分析 MUC1-C 对全局转录谱的影响。差异表达和等级排序分析用于基因集富集分析（GSEA）。通过定量逆转录 PCR 和免疫印迹法确认基因表达。分析了癌症基因组图谱乳腺浸润性癌（TCGA-BRCA）和乳腺癌国际联合会（METABRIC）数据集，以研究 MUC1 对 GSEA、细胞类型富集以及肿瘤免疫功能障碍和排除的影响。分析了 TNBC 样本的单细胞 scRNA-seq 数据集，以确定肿瘤细胞内 MUC1 与选定基因之间的归一化表达关联。
我们的结果表明，MUC1-C 是 TNBC 转录组的主要调节因子，MUC1-C 诱导的基因表达受 STAT1 和 IRF1 驱动。我们发现 MUC1-C 激活炎症性干扰素（IFN）-γ驱动的 JAK1→STAT1→IRF1 途径，并诱导 IDO1 和 COX2/PTGS2 效应物，它们在免疫抑制中发挥关键作用。通过分析人类批量和 scRNA-seq 数据集，扩展了 MUC1-C 参与激活免疫抑制 IFN-γ途径的作用。我们进一步证明 MUC1 与 TNBC TIME 中 CD8+T 细胞的耗竭和功能障碍有关。
这些发现表明，MUC1-C 将免疫抑制 IFN-γ途径的激活与 TNBC TIME 中 TIL 的耗竭整合在一起，并为 MUC1-C 作为一种潜在的治疗靶点提供了支持，可单独或与 ICI 联合用于治疗 TNBC。具有重要转化意义的是，MUC1-C 是一种可靶向药物靶点，具有嵌合抗原受体（CAR）T 细胞、抗体药物偶联物（ADC）和一种正在临床开发中的功能性抑制剂。
