Multiple sclerosis (MS) is a progressive, chronic, and highly disabling neuroinflammatory disorder characterized by demyelination and T cell–driven inflammation. Pathogenic T cells play a central role in MS, but effective therapeutic targeting remains challenging. Here, we identified ankyrin repeat domain–containing protein 55 (ANKRD55) as a key regulator of T cell function by single-cell transcriptomic analysis of cerebrospinal fluid and blood from MS patients. ANKRD55 was predominantly ...