Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system that causes progressive disability. Recently, a new drug called tolebrutinib became the first treatment to show success in people with secondary progressive MS without disease activity — a form of the disease for which there were few effective treatment options. While the results are promising, the precise mode of action remains unclear. The research project uses specialized mouse models to identify the cell-types affected by the medication, which could explain tolebrutinib’s treatment effect. Further, the scientists aim to establish cutting-edge genetic techniques to study these cells individually. These findings will help optimize treatment and develop new therapeutic strategies for people with MS.