Single-cell transcriptomic analysis of mammary tumors reveals distinct patterns of hierarchical and subtype heterogeneity

Breast cancer stem cells (BCSCs) contribute to intra-tumoral heterogeneity and therapeutic resistance. However, the binary concept of universal BCSCs co-existing with bulk tumor cells is over-simplified. Through single-cell RNA-sequencing, we found that Neu, PyMT and BRCA1-null mammary tumors each corresponded to a spectrum of minimally overlapping cell differentiation states without a universal BCSC population. Instead, our analyses revealed that these tumors contained distinct lineage-specific tumor propagating cells (TPCs) and this is reflective of the self-sustaining capabilities of lineage-specific stem/progenitor cells in the mammary epithelial hierarchy. By understanding the respective tumor hierarchies, we were able to identify CD14 as a TPC marker in the Neu tumor. Additionally, single-cell breast cancer subtype stratification revealed the co-existence of multiple breast cancer subtypes within tumors. Collectively, our findings emphasize the need to account for lineage-specific TPCs and the hierarchical composition within breast tumors, as these heterogenous sub-populations can have differential therapeutic susceptibilities. We compared the gene expression profile at single-cell level of four breast tumor models in mice.

乳腺癌干细胞（Breast cancer stem cells, BCSCs）可促进肿瘤内异质性与治疗耐药性的产生。然而，认为通用型乳腺癌干细胞与实体瘤细胞共存的二元概念过于简化了实际情况。通过单细胞RNA测序技术，我们发现Neu、PyMT以及BRCA1敲除型乳腺肿瘤各自对应一组重叠度极低的细胞分化状态，不存在通用型乳腺癌干细胞群体。与之相反，我们的分析显示，这类肿瘤中存在不同的谱系特异性肿瘤增殖细胞（lineage-specific tumor propagating cells, TPCs），这一现象反映了乳腺上皮层级中谱系特异性干细胞/祖细胞的自我维持能力。通过解析各类肿瘤的层级结构，我们成功鉴定出CD14可作为Neu型乳腺肿瘤中的肿瘤增殖细胞标志物。此外，乳腺癌单细胞亚型分层分析显示，单枚肿瘤内部可同时存在多种乳腺癌亚型。综上，我们的研究结果强调，需充分考虑乳腺肿瘤内的谱系特异性肿瘤增殖细胞及其层级组成，因为这些异质性亚群对治疗的敏感性存在差异。本研究对小鼠体内四种乳腺肿瘤模型的单细胞水平基因表达谱进行了对比分析。