The activity of tertiary lymphoid structures in high grade serous ovarian cancer is governed by site, stroma, and cellular interactions

Most high grade serous ovarian cancers (HGSOC) originate in the fallopian tube but spread to the ovary and peritoneal cavity, highlighting the need to understand antitumor immunity across HGSOC sites. Using spatial analyses, we discover that tertiary lymphoid structures (TLS) within ovarian tumors are less developed compared with TLS in fallopian tube or omental tumors. We reveal transcriptional differences across a spectrum of lymphoid structures, demonstrating that immune cell activity increases when residing in more developed TLS and produce a prognostic, spatially derived TLS signature from HGSOC tumors. We interrogate TLS-adjacent stroma and assess how normal mesenchymal stem cells MSCs (nMSCs) may support B cell function and TLS, contrary to cancer-educated MSCs (CA-MSCs) which negate the prognostic benefit of our TLS signature, suggesting that pro-tumorigenic stroma could limit TLS formation. FFPE embedded HGSOC specimens were selected from the following anatomic sites: Fallopian Tube, Omentum and Ovary. Non-malignant lymph node was selected as a control. Samples were stained with morphology markers: CD20, CD45, PanCk and processed through the Nanostring GeoMx Digital Spatial Profiler. Using morphology stains, ROI categories were called according to staining combinations. The (v1.0) Human NGS Whole Transcriptome Atlas RNA was used for all samples.