Electronic Poster | Session 1

060 – Single-cell profiling of cerebrospinal fluid lymphocytes from monozygotic twins discordant for multiple sclerosis

Julia Hansen (1§) – Eduardo Beltrán (1§) – Lisa Ann Gerdes (1§) – Reinhard Hohlfeld (1*) – Klaus Dornmair (1*)
Institute of Clinical Neuroimmunology, Hospital of the LMU Munich, Munich, Germany (1)

Inflammatory features of multiple sclerosis (MS) include T- and B-cell lymphocyte accumulations in central nervous system (CNS) and cerebrospinal fluid (CSF), with activated CD8+ T-cells as the dominating population in the CNS. The function of the lymphocytes that invade brain tissue and the CSF is still enigmatic. We here investigated a cohort of 4 monozygotic twin pairs discordant for MS where one twin had established MS and the co-twin was clinically healthy, but carried a maximal familial risk for developing MS. Altogether we analyzed 4 MS patients, 4 healthy controls and 6 subjects with “subclinical neuro-inflammation” (SCNI). These subjects were clinically “healthy” co-twins who showed small MRI lesions, indicating a presumably preclinical form of MS. Of note, four of the SCNI patients had oligoclonal bands (OCBs), which is a hallmark of established MS. We used single-cell profiling to compare gene expression patterns of lymphocytes from CSF of MS-discordant monozygotic twin pairs. This enabled us to investigate disease-relevant changes in gene-expression patterns in genetically identical subjects and revealed insights into very early MS pathogenesis. We identified clonally expanded CD8+ T cells, plasmablasts, and – to a lesser extent – CD4+ T cells. Clonal expansions are thought to arise from sustained stimulation by antigen and are therefore presumably of pathogenic relevance. Moreover, expanded T cells showed characteristics of an activated tissue resident memory T (TRM) cell phenotype. TRM cells express the early activation marker CD69, pro-inflammatory cytokines including IFNG and IL-2 and upregulate tissue retention molecules that prevent them from leaving the CSF. In particular, molecules involved in T cell egress as S1PR1, CCR7, or SELL were strongly downregulated in expanded cells from MS patients but downregulation was also observed in SCNI. Further, expanded plasmablast clones were detected only in patients with OCBs. Our data provide evidence for very early concomitant activation of three components of the adaptive immune system in MS, with a notable contribution of activated, clonally expanded TRM-like CD8+ T cells.