P05.14.b Multi-Layered Cerebrospinal Fluid Liquid Biopsy of Inflammatory and Oncological CNS Diseases

Abstract BACKGROUND For diagnosis of central nervous system (CNS) pathologies, invasive procedures such as tissue biopsies are often indicated. The use of cerebrospinal fluid (CSF) for a liquid biopsy (LB) has promise as a minimal invasive tool, not only for diagnosis but also for therapy monitoring and gaining mechanistic insights into CNS pathologies. In this context, cell-free DNA (cfDNA) has emerged as a key analyte, particularly for tumour classification. However, additional analytes and approaches, such as profiling the CSF proteome or analysing the adaptive immune receptor repertoire, also hold significant potential as biomarkers for deepening our understanding of disease mechanisms. Notably, the diversity and clonality of adaptive immune receptors are critical indicators of immune competence, and immune dynamics are increasingly recognized as central to the development and therapeutic response of CNS disorders, including brain tumours. MATERIAL AND METHODS CSF cfDNA was isolated from the cell-free supernantant and profiled utilising Oxford nanopore-based sequencing, followed by tumour classification with NanoDx (n=40). In parallel, nanopore-based sequencing of the CSF T cell receptors was performed in patients with inflammatory and neoplastic CNS conditions to evaluate the T cell receptor repertoire. To complement the multi-omics CSF profiling, the CSF proteome was analysed by mass-spectometry (n=58). RESULTS By using this multi-layered analysis, disease-specific CSF profiles were distinguishable. In patients with leptomeningeal disease, distinct CSF signatures of the proteome were identified. These particularly involved inflammatory pathways and immune checkpoints differentiated from CSF in inflammatory conditions as well as in brain tumour patients without LMD. CONCLUSION By taking advantage of the possibilities of an advanced LB strategy including multiple analytes a broad range of information can be gathered from a single CSF sample. Their integration results in a detailed picture of disease and immunity mechanisms. LBs therefore show promise not only in diagnostics but also in monitoring disease progression and detecting resistance. They can aid in the guidance of personalised treatment in neuro-oncological and neuro-inflammatory conditions. SUPPORT/DISCLOSURE SK was supported for this project by the INDEEP Clinician Scientist Program (German Research Foundation/DFG, 493624332). SK, KJW, and PSZ were funded by the Mildred Scheel Career Center Frankfurt (MSNZ).