• Time to Sustained Accumulation of Disability (SAD) [ Time Frame: 2 years ] [ Designated as safety issue: No ]
  
• Relapse Rate [ Time Frame: 2 years ] [ Designated as safety issue: No ]
  

• Proportion of patients who are relapse free at Year 2 [ Time Frame: 2 years ] [ Designated as safety issue: No ]
  
• Change from baseline in EDSS [ Time Frame: 2 years ] [ Designated as safety issue: No ]
  
• Acquisition of disability as measured by change from baseline in MSFC [ Time Frame: 2 years ] [ Designated as safety issue: No ]
  
• Percent change from baseline in MRI-T2 hyperintense lesion volume at Year 2 [ Time Frame: 2 years ] [ Designated as safety issue: No ]
  

Every patient will receive active treatment; there is no placebo. Patients who qualify will be randomly assigned to treatment with either 12mg alemtuzumab, 24 mg alemtuzumab, or Rebif® at a 2:2:1 ratio (ie, there is a 4-in-5 chance patients will be assigned to receive alemtuzumab treatment and a 1-in-5 chance patients will be assigned to receive Rebif® treatment). Alemtuzumab will be administered in two annual cycles, once at the beginning of the study and again 1 year later. Rebif® will be self-injected 3 times per week for 2 years. All patients will be required to return to their study site every 3 months for neurologic assessment. In addition, a safety-related blood test will be performed at least monthly. Participation in this study will end 2 years after the start of treatment for each patient. Additionally, all patients who receive alemtuzumab will be followed in an extension study for safety for at least 3 years after their last dose alemtuzumab. Patients who receive Rebif® and complete 2 years on study may be eligible to receive alemtuzumab in an extension study.

Inclusion Criteria:

• Diagnosis of MS and MRI scan demonstrating white matter lesions attributable to MS
• Onset of MS symptoms within 10 years
• EDSS score 0.0 to 5.0
• ≥2 MS attacks within 24 months, with ≥1 attack within 12 months
• ≥1 MS attack (relapse)during treatment with a beta interferon therapy or glatiramer acetate after having been on that therapy for at least 6 months within 10 years
• Neurologically stable for the 30 days prior to the date the Informed Consent Form is signed

Exclusion Criteria:

• Previous treatment with alemtuzumab
• Previous treatment with any investigational drug (i.e. a medication that is not approved at any dose or for any indication)
• Treatment with natalizumab, methotrexate, azothioprine or cyclosporine in the past 6 months
• Previous treatment with mitoxantrone, cyclophosphamide, cladribine, rituximab, or any other immunosuppressive, or cytotoxic therapy (other than steroid treatment)
• Any progressive form of MS
• Any disability acquired from trauma or another illness that could interfere with evaluation of disability due to MS
• Major systemic disease that cannot be treated or adequately controlled by therapy
• Active infection or high risk for infection
• Autoimmune disorder (other than MS)
• Impaired hepatic or renal function
• History of malignancy, except basal skin cell carcinoma
• Medical, psychiatric, cognitive, or other conditions that compromise the patient's ability to understand the patient information, to give informed consent, to comply with the trial protocol, or to complete the study
• Known bleeding disorder
• Of childbearing potential with a positive serum pregnancy test, pregnant, or lactating
• Current participation in another clinical study or previous participation in CAMMS323
• Previous hypersensitivity reaction to any immunoglobulin product
• Known allergy or intolerance to interferon beta, human albumin, or mannitol
• Intolerance of pulsed corticosteroids, especially a history of steroid psychosis
• Inability to self-administer subcutaneous (SC) injections or receive SC injections from caregiver
• Inability to undergo MRI with gadolinium administration
• Unwilling to use a reliable and acceptable contraceptive method throughout the study period (fertile patients only)