The Molecular Features and Spatial Architecture of Bladder Ewing Sarcoma - Expert Commentary
The investigators collected tumor and normal tissue samples from one patient with ES/PNET and one patient with urothelial carcinoma (UC), resulting in four samples. ScRNA-seq processing resulted in a total of 15,037 cells and 28 clusters across all samples after filtering. Annotation using well-known markers revealed ten major cell types: T cells, fibroblasts, stromal cells, endothelial cells, epithelial cells, mast cells, macrophages, smooth muscle cells, neutrophils, and B cells. There was a higher amount of T cells and a lower amount of endothelial and smooth muscle cells in bladder ES/PNET and UC tumor tissues compared to normal tissues. Epithelial and mast cells had a higher presence in bladder ES/PNET tumor tissues and a decreased presence in UC tissues. Epithelial cells were found to strongly express Ewing sarcoma marker genes in bladder ES/PNET tumor tissue.
Spatial transcriptomics was subsequently used to characterize the spatial distribution of the diverse cell types. This revealed heterogeneous spatial and quantitative distribution of cell types across normal versus tumor tissues and ES/PNET versus UC tissues, particularly epithelial cells. The investigators then focused on epithelial clusters in the scRNA-seq dataset, identifying an increase in epithelial cells in the ES/PNET tumor samples and a decrease in the UC tumor sample. Furthermore, a specific subcluster of epithelial cells was found only in the ES/PNET (ES-Epi) but not in the UC tumor sample. Using gene regulatory network analyses, the investigators characterized key transcription factors involved in this novel ES-Epi subcluster. Gene ontology and pathway analysis on ES-Epi cells revealed enrichment in the reactive oxygen species response, gland development, protein kinase activity, MAPK signaling, and tumor growth factor b (TGF-b) signaling. Mast cells also exhibited an increase in the ES/PNET tumor and a decrease in the UC tumor. Subclustering of mast cells revealed a mast cell subtype that was specific to the ES/PNET tumor sample (ES-Mast). The investigators then identified intercellular interactions between the mast cells and ES-Epi cells. These interactions were found to be dependent on the TNFSF12-TNFRSF12A ligand-receptor pair, which is known to contribute to angiogenesis and tumor survival in UC. In line with this, TNFRSF12A expression was significantly upregulated in bladder ES/PNET. Enavatuzumab, an antibody that targets TNFSF12, was tested on an ES cell line and was found to reduce cell migration.
By integrating several methods, this study provided a detailed understanding of cellular, molecular, and intercellular mechanisms underpinning bladder ES/PNET. The investigators identified a potential therapeutic option that can be tested in further studies.
Written by: Bishoy M. Faltas, MD, Director of Bladder Cancer Research, Englander Institute for Precision Medicine, Weill Cornell Medicine
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