This prospective, controlled (comparison to the period prior to natalizumab treatment), single-arm, open-label, multi-centre, phase IV study aims to evaluating the concept of natalizumab de-escalation to interferon-beta-1b e.o.d in relapsing-remitting multiple sclerosis patients, who consider stopping natalizumab due to a benefit-risk assessment. In particular, to evaluating if interferon beta-1b treatment may be able to overcome the recurrence of significant clinical and radiological disease activity after natalizumab cessation and may keep disease activity better under control as compared to the time prior to natalizumab.