What type of multiple sclerosis is Tysabri (natalizumab) indicated to treat in adults?

Tysabri (natalizumab) is indicated as sole disease-modifying therapy for adults with highly active relapsing-remitting multiple sclerosis despite a full, adequate course of ≥1 DMT, or rapidly evolving severe disease defined by ≥2 disabling relapses/year plus ≥1 gadolinium-enhancing brain MRI lesion or significantly increased T2 lesion load versus a recent MRI.