CSF single-cell RNA sequencing reveals clonally expanded CD4+ stem cell-like memory T cells in GAD65-antibody associated neurological syndromes

BackgroundGlutamic acid decarboxylase (GAD) antibody-associated autoimmune neurological syndromes (AINS) are a spectrum of autoimmune-mediated CNS disorders. While antibodies targeting the 65 kDa isoform of GAD are of high diagnostic value, T cell mediated cytotoxicity has been identified as a key component of disease pathogenesis. The precise pathophysiological mechanisms by which the disease is triggered and maintained, however, remain incompletely understood. MethodsWe performed single-cell transcriptome and immune repertoire sequencing (sc-seq) in CSF and blood of 8 anti-GAD65 AINS patients compared to 8 non-inflammatory controls. Monoclonal antibodies (mAbs) were synthesized from B cell receptor (BCR) data to evaluate the B cellular immune response. FindingsWe identified an increase and expansion of activated CD4+ stem cell-like memory T cells (TSCM) in the CSF of anti-GAD65 AINS patients. Expanded T cells showed increased expression of proinflammatory genes. The mAb analysis revealed a high frequency of GAD65-reactive BCRs in the CSF of anti-GAD65 AINS patients with increased somatic hypermutations compared to non-GAD-reactive BCRs and BCRs from controls. ConclusionsSc-seq identified clonally expanded CD4+ TSCM in the CSF of anti-GAD65 AINS patients harboring cytotoxic properties likely contributing to disease pathogenesis. GAD-reactive B cells circulate in the CSF of anti-GAD65 AINS patients further supporting the concept of an antigen-specific intrathecal immune response. Future studies need to clarify the actual pathogenicity of these immune cells and the link between T and B cellular immune mechanisms in the pathogenesis of anti-GAD65 AINS. FundingGerman Research Foundation (ERARE18-202 UltraAIE), German Federal Ministry of Education and Research (CONNECT GENERATE (2.0); 01GM1908A and 01GM2208A).