 - Any Rebif participants from CAMMS223, CAMMS323, or CAMMS324 who met any of the following criteria. In addition, these participants must be screened for disqualifying safety concerns before receiving alemtuzumab treatment. a Did not wish to receive alemtuzumab; b Ongoing participation in any other investigational study, unless approved by Genzyme; c Had received alemtuzumab off-label ie, outside of one of the prior Genzyme-sponsored studies; d Known bleeding disorder or therapeutic anticoagulation; e Diagnosis of idiopathic thrombocytopenia purpura or other autoimmune hematologic abnormality; f History of malignancy, except basal cell skin carcinoma; g Intolerance of pulsed corticosteroids, especially a history of steroid psychosis h Significant Autoimmune disorder other than MS; i Major psychiatric disorder or epileptic seizures not adequately controlled by treatment; j Active infection or high risk for infection k Unwilling to use a reliable and acceptable contraceptive method during and for at least 6 months following each alemtuzumab treatment cycle fertile participants only. 