Multiple sclerosis (MS) is an inflammatory neurological disease of the central nervous system with a subclinical phase preceding frank neuroinflammation. CD8^(+) T cells are abundant within MS lesions, but their potential role in disease pathology remains unclear. Using high-throughput single-cell RNA sequencing and single-cell T cell receptor analysis, we compared CD8^(+) T cell clones from the blood and cerebrospinal fluid (CSF) of monozygotic twin pairs in which the cotwin had either no …