Natalizumab is a recombinant, humanized IgG4 monoclonal antibody, binds to α4β1-integrin and blocks its interaction with vascular cell adhesion molecule-1 (VCAM-1). Natalizumab can be used for the treatment of relapsing remitting multiple sclerosis and Crohn's disease. Natalizumab is also the first targeted therapy which blocks an essential mechanism for lymphocyte entry to the CNS and thus prevents acute demyelinating relapses.