OS01.5.A THE USE OF MULTIOMICS IN THE IDENTIFICATION AND CHARACTERISATION OF TERTIARY LYMPHOID STRUCTURES IN GLIAL TUMORS

Abstract BACKGROUND Tertiary Lymphoid Structures (TLSs) are organized immune cell aggregates present in non-lymphoid tissues for the initiation and maintenance of local and systemic anti-tumor immune response. The presence of TLS has been associated with better prognosis and clinical outcome in several cancer types, including lung and melanoma. However, the formation of TLS and its potential role in intra-tumoral immune response remains unclear. TLS are particularly interesting in gliomas as tumor-infiltrating lymphocytes is inefficient possibly due to the immunosuppressive microenvironment and the presence of the blood brain barrier. This study aims to identify and characterize the presence of TLS in glioma patients, to understand its role in generating a local immune response against tumors and identify potential biomarkers. We characterized TLS in glioma by immunohistochemistry, RNA sequencing from TLS positive tumors and used spatial transcriptomics to map TLS gene expression within the tumors. MATERIAL AND METHODS Of the 1274 adult patients with diffuse glioma, resected between 2015 and 2021, a total of 663 FFPE-tissue samples were available for B cell infiltration IHC-screening. Subsequently, the TLS+ samples were characterized using spatial transcriptomics and Opal-TSA mIHC, a spatial proteomic method that enables a simultaneous detection of 6 antigens in FFPE tumor tissues. A selection of TLS+ and matched TLS- tumors were subjected to bulk-tissue whole RNA sequencing. Downstream analysis such as cell-type specific transcriptional deconvolution and differential gene expression were performed. Furthermore, a multimodal analysis of TLS in glioma was conducted by combining the genomic, transcriptomic, spatial proteomics and clinical data. RESULTS B cell accumulations were observed in 13.1% of all gliomas. Small CD20 B cells accumulation, named perivascular immune cells (PVIC), and TLS were observed in 10.7% and 2.4%, respectively. We investigated the overall survival of patients in the TLS+, TLS- and PVIC groups. So far, no significant differences were observed. The transcriptomic analyses of TLS+ with TLS- tumors revealed an upregulation of genes related to innate and adaptive immune responses, complement cascade and the extracellular matrix. Genes associated with neural differentiation were expressed higher in TLS- compared to TLS+ tumors. Moreover, our multimodal analysis revealed the presence of distinct classes of TLS in glioma which differed in their cellular and molecular compositions. CONCLUSION Using a multimodal analysis, this study identified B cell accumulation and TLS in glioma patients. In contrast to other cancer types, the presence of TLS in glioma did not correlate with a higher overall survival. However, the role of TLS in glioma and their prognostic and therapeutic relevance remains under investigation with further analyses currently underway.