Study Purpose: This study is testing a new drug called frexalimab for adults with a type of multiple sclerosis (MS) called nonrelapsing secondary progressive multiple sclerosis (nrSPMS). Multiple sclerosis (MS) is a disease that affects the brain and spinal cord, causing problems with movement and feeling. The goal is to see if frexalimab can slow down the worsening of disability and if it is safe to use.

Study Design: Participants will be randomly given either frexalimab or a placebo, which is a harmless pill that doesn’t contain the active drug, to compare their effects. The study will last between 27 to 51 months, depending on when enough results are gathered. The drug will be given for 12 to 51 months, and participants will have up to 27 visits to the study center.

• Study duration: 27 to 51 months.
• Up to 27 visits: Monthly for 6 months, then every 3 months.
• Participants must meet certain health criteria and have no history of certain illnesses.