4. Inflammatory disease despite primary disease modifying therapy with at least 3 months of interferon. Failure is defined as two or more clinical relapses with documented neurologic changes within the year prior to the study. (NOTE: Relapses must have required treatment with corticosteroids. Sensory only relapses are excluded.) Failure may also be defined as one relapse within the year prior to study if there is evidence on MRI of active inflammation (i.e., gadolinium enhancement).