Mesenchymal stem cells and fibroblasts underly microvascular proliferation and are associated with immunosuppression and poor outcome in glioma

Immunotherapies are revolutionary cancer treatments, but resistance in solid tumors such as glioma is well-established. Cancer-associated fibroblasts are emerging as important stromal elements that contribute to treatment resistance and immunosuppression. However, cancer-associated fibroblasts and their theoretical cells of origin, mesenchymal stem cells, have not been resolved at the single-cell level directly from human glioma tissue. There is evidence that mesenchymal stem cells reside in the perivascular niche. Thus, we hypothesized glioma-associated mesenchymal stem cells and fibroblasts could be found in the perivascular niche and that they contribute to local immunosuppression and pathology such as microvascular proliferation. Microvascular proliferation is a defining histopathologic feature of high-grade glioma and independent poor prognostic marker in glioma, brain metastases, and other systemic cancers. Developing targets against microvascular proliferation could lead to biomarkers and treatments to halt progression. In this study, we demonstrate that mesenchymal stem cells and fibroblasts, herein referred to as perivascular stromal cells, underly microvascular proliferation in contrast to the classical teaching it is due to endothelial cell hyperplasia. Furthermore, we capture perivascular stromal cells in a single-cell RNA velocity analysis that suggests mesenchymal stem cells are fibroblast progenitors. With signal transduction network generation and digital spatial profiling, we show these cells participate in immunosuppressive crosstalk with myeloid cell populations in the perivascular niche. Lastly, we identify a gene signature rich in extracellular matrix molecules derived from perivascular stromal cells that have undergone microvascular proliferation with implications on overall survival in glioma and five other cancers.

免疫治疗是革命性的癌症治疗手段，但胶质瘤等实体瘤的治疗耐药性已被广泛证实。癌相关成纤维细胞（cancer-associated fibroblasts）作为重要的基质组分，在治疗耐药与免疫抑制中的作用正日益受到关注。然而，直接从人脑胶质瘤组织中以单细胞水平解析癌相关成纤维细胞及其理论起源细胞——间充质干细胞（mesenchymal stem cells）的相关研究仍未得到充分开展。已有研究证实，间充质干细胞定位于血管周围微环境（perivascular niche）。据此，我们提出假设：胶质瘤相关间充质干细胞与成纤维细胞可存在于血管周围微环境中，并参与局部免疫抑制及微血管增殖等病理过程。微血管增殖是高级别胶质瘤的标志性组织病理学特征，同时也是胶质瘤、脑转移瘤及其他实体癌的独立不良预后标志物。靶向微血管增殖的研究有望开发出用于阻滞疾病进展的生物标志物与治疗方案。在本研究中，我们证实：与传统观点认为微血管增殖源于内皮细胞增生不同，间充质干细胞与成纤维细胞（本文统称为血管周围基质细胞（perivascular stromal cells））是微血管增殖的核心驱动因素。此外，我们通过单细胞RNA速率分析（single-cell RNA velocity analysis）捕获到血管周围基质细胞，结果提示间充质干细胞是成纤维细胞的祖细胞。通过信号转导网络构建与数字空间分析（digital spatial profiling），我们证明这些细胞可与血管周围微环境中的髓系细胞群发生免疫抑制性串扰。最后，我们鉴定出一套富含细胞外基质分子的基因特征谱，该特征谱源自发生微血管增殖的血管周围基质细胞，且其表达水平与胶质瘤及其他五种癌症的总生存期密切相关。