The MRI study is designed to identify possible mechanisms by which alemtuzumab acts to protect the brain from inflammation and how it may enhance repair through remyelination.

To identify specific changes in T cell subsets and functions in Relapsing Remitting Multiple Sclerosis.

Inclusion Criteria

1. Signed, informed consent form (ICF)
2. Age 18 to 50 years old (inclusive) as of signing the ICF
3. Diagnosis of MS per update of McDonald criteria, and cranial MRI scan demonstrating white matter lesions attributable to MS within 10 years of screening
4. Onset of MS symptoms (as determined by a neurologist) within 15 years of screening
5. EDSS score 0.0 to 5.0 (inclusive)
6. >=2 MS attacks (first episode or relapse) occurring in the 24 months prior to screening, with >=1 attack in the 12 months prior to screening, with objective neurological signs confirmed by a physician
7. Subjects previously enrolled and randomized to interferon beta 1a in the CARE-MS 323 and 324 studies, and who will be treated with Alemtuzumab through the CARE-MS extension study will be eligible to participate in the immunology and MRI studies of this protocol.

Exclusion Criteria

1. Received prior therapy for MS other than corticosteroids within 28 days of screening; e.g., interferons, IV immunoglobulin, and glatiramer acetate
2. Exposure to natalizumab within 6 months of screening
3. Any prior exposure to mitoxantrone, mycophenolate mofetil, azathioprine, cladribine, cyclophosphamide, cyclosporine A, methotrexate, rituximab, or any other immunosuppressive agent other than systemic corticosteroid treatment
4. Has any progressive form of MS
5. History of malignancy (exception for basal cell skin carcinoma)
6. Previous hypersensitivity reaction to other immunoglobulin product
7. Intolerance of pulsed corticosteroids, especially a history of steroid psychosis
8. CD4+, CD8+, or CD19+ (i.e., absolute CD3+CD4+, CD3+CD8+, or CD19+/mm3) count \