Ocrevus (ocrelizumab), a monoclonal antibody that is used to treat various forms of relapsing multiple sclerosis (MS).  

MS is a chronic autoimmune disease of the central nervous system (CNS) that affects millions of people worldwide. The disease causes inflammation and damage to the protective coating around nerve fibers in the brain and spinal cord, leading to a wide range of symptoms including numbness, weakness, difficulty walking, and vision problems. 

B cells are a type of immune cell that plays a crucial role in the development of MS. When activated, B cells produce antibodies that attack the myelin sheath that surrounds nerve fibers in the CNS, leading to inflammation and damage. CD20 is a protein that is expressed on the surface of B cells, making it a promising target for MS treatments. 

Ocrevus works by binding to CD20 on the surface of B cells, leading to their destruction. This reduces the number of B cells in the bloodstream and in the CNS, which in turn reduces the production of antibodies that attack the myelin sheath. By targeting CD20-expressing B cells, Ocrevus can help to slow the progression of MS and reduce the frequency and severity of relapses.