Investigating the CXCR4/CXCL12 Axis to Predict Multiple Sclerosis Symptom Onset 2259236

Introduction Radiologically Isolated Syndrome (RIS) is a pre-symptomatic form of Multiple Sclerosis (MS), where lesions are present in the central nervous system (CNS). Although RIS can now be diagnosed as MS, not all people will progress. Accessible approaches to prognose pwRIS remain to be developed. We propose to study peripheral blood cell (PBMC) and cerebrospinal fluid (CSF) samples of pwRIS, pwMS and healthy (HC) individuals. Selected for this study is the lymphocyte migration molecule CXCR4 and its ligand CXCL12. Methods A cohort of 48 pwRIS with 4 years follow up, as well as age- and sex-matched pwMS and HC were used for the study. We further divided pwRIS based on disease activity within a year of sample collection. An Ella assay was performed on CSF to titer levels of CXCL12. PBMCs were phenotyped using CyTOF, and flow cytometry following stimulation, focusing on T cell migration and activation. Single-cell RNA and TCR sequencing was performed to correlate transcriptomic and TCR repertoire changes with disease activity. Results CXCL12 levels in pwRIS and pwMS CSF were increased significantly in comparison to HC. These levels positively correlated to GFAP but not NfL. Upregulation of CXCR4 was observed on multiple lymphocyte subsets, particularly on CD8 effector T cells in pwRIS with disease activity, as found by CyTOF and flow cytometry. CXCR4 expression also correlated to cytokine production in stimulated PBMCs. Conclusion We have shown that CXCL12, a proposed ligand for early CNS chemotaxis and entry, is upregulated in the CSF of pwRIS and pwMS. CXCL12 correlates with other markers of MS progression, suggesting a potential use for early prognosis. CXCR4 is upregulated on CD8 effectors, suggesting an aberrant immune response leading to early CNS trafficking, which is correlated with increased T cell reactivity and disease activity. These findings will be central in the improvement in clinical care by providing a prognostic tool, while understanding the pathophysiology of early disease.