For solid tumors, extravasation of cancer cells and their survival in circulation represents a critical stage of the metastatic process that lacks complete understanding. Gaining insight into interactions between circulating tumor cells (CTCs) and other peripheral blood mononuclear cells (PBMCs) may provide valuable prognostic information. The purpose of this study was to use single‐cell RNA‐sequencing (scRNA‐seq) of liquid biopsies from breast cancer patients to begin defining intravascular interactions. We captured CTCs from the peripheral blood of breast cancer patients using size‐exclusion membranes followed by scRNA‐seq of enriched CTCs and carry‐over PBMCs. Transcriptome analysis identified two populations of CTCs: one enriched for transcripts indicative of estrogen responsiveness and increased proliferation and another enriched for transcripts characteristic of reduced proliferation and epithelial–mesenchymal transition (EMT). We applied interactome and pathway analysis to determine interactions between CTCs and other captured cells. Our analysis predicted for enhanced immune evasion in the CTC population with EMT characteristics. In addition, PD‐1/PD‐L1 pathway activation and T cell exhaustion were predicted in T cells isolated from breast cancer patients compared with normal T cells. We conclude that scRNA‐seq of breast cancer CTCs generally stratifies them into two types based on their proliferative and epithelial state and differential potential to interact with PBMCs. Better understanding of CTC subtypes and their intravascular interactions may help design treatments directed against CTCs with high metastatic and immune‐evasive competence.

中文翻译：

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循环乳腺癌细胞异质性及其与外周血单个核细胞相互作用的分析。

对于实体瘤，癌细胞的外渗及其在循环中的存活代表了缺乏完全了解的转移过程的关键阶段。深入了解循环肿瘤细胞 (CTC) 和其他外周血单核细胞 (PBMC) 之间的相互作用可能会提供有价值的预后信息。本研究的目的是使用乳腺癌患者液体活检的单细胞 RNA 测序 (scRNA-seq) 来开始定义血管内相互作用。我们使用大小排阻膜从乳腺癌患者的外周血中捕获 CTC，然后是富集 CTC 和残留 PBMC 的 scRNA-seq。转录组分析确定了两个 CTC 群体：一种富含表明雌激素反应性和增殖增加的转录物，另一种富含增殖减少和上皮间质转化 (EMT) 特征的转录物。我们应用相互作用组和通路分析来确定 CTC 与其他捕获细胞之间的相互作用。我们的分析预测了具有 EMT 特征的 CTC 群体中增强的免疫逃避。此外，与正常 T 细胞相比，从乳腺癌患者分离的 T 细胞中预测了 PD-1/PD-L1 通路激活和 T 细胞耗竭。我们得出结论，乳腺癌 CTC 的 scRNA-seq 通常根据它们的增殖和上皮状态以及与 PBMC 相互作用的不同潜力将它们分为两种类型。