Raza, S. A.; Enose-Akahata, Y.; Blazier, A.; Guerra, L. M.; Beck, E. S.; Gaitan, M. I.; Ngouth, N.; Drijvers, J. M.; Dammer, E. B.; Moodley, D.; Johnson, K. R.; Absinta, M.; TURNER, T. J.; Ransohoff, R. M. J.; Jacobson, S.; Ofengeim, D.; Cahir-McFarland, E.; Reich, D. S.

Chronic neuroinflammation and neurodegeneration are critical but unresolved drivers of disability accumulation in progressive multiple sclerosis (MS). Chronic active white matter lesions (CAL), identifiable radio-logically as paramagnetic rim lesions (PRL), indicate progression-relevant chronic neuroinflammation. Using single-cell transcriptomics (scRNAseq) and T-cell receptor sequencing (scTCR-seq), we profiled cerebrospinal fluid (CSF) and blood immune cells of 34 radiologically characterized adults with MS (17 untreated, 6 treated with B-cell-depletion) and 5 healthy controls. Coupled with proteomics, we found PRL-associated enrichment of interferon (IFN) signaling and upregulation of TCR signaling in CSF and blood. This was accompanied by clonal expansion of CD8+ T effector memory (TEM) cells, with the highly expanded clonal cells exhibiting T helper type 1 (TH1) and cytotoxic profiles. Validating the cytotoxic immune profile in blood using flow cytometry, we identified a cellular correlate of PRL exhibiting features of CD8+ TEMRA cells. Despite B-cell depletion, PRL-associated neuroinflammation, driven by myeloid activation and CD8+ T-cell cy-totoxicity, persisted. Serum and CSF proteomic networks showed PRL-pertinent signatures, including net-works unaffected by B-cell depletion. Using in silico perturbation, we nominated therapeutic targets, including MYD88, TNF, MYC, TYK2, JAK2, and BTK, for alleviating chronic neuroinflammation in MS. Our findings highlight mechanisms of chronic neuroinflammation in MS and point to potential biomarkers for moni-toring disease progression.