Some people who have hemophilia A develop antibodies to the injected clotting factor. The antibodies are called inhibitors. Inhibitors may make it more difficult to treat bleeding episodes because the body's natural defense system (immune system) interferes with the function of replacement clotting factors. In these cases, treatment may require specially engineered replacement clotting factors. Other treatment for clotting factor inhibitors includes therapy to suppress the immune system (immunosuppressive therapy).