Kesimpta is not a chemotherapy drug, but it is an immunosuppressant.Chemotherapy works by killing rapidly multiplying cells in the body. It’s typically used to treat cancer because cancer cells usually multiply quickly.Kesimpta is a type of drug called an immunosuppressant, which aims to weaken the immune system. It’s believed that Kesimpta works by decreasing the activity of your immune system. This helps ease the symptoms of multiple sclerosis (MS). For more information on how Kesimpta works, see the “How Kesimpta works” section.