Inclusion Criteria:

• Patients with a first acute or subacute, well-defined neurological event consistent with demyelination (i.e. optic neuritis confirmed by an ophthalmologist, spinal cord syndrome, brainstem/cerebellar syndromes)
• Onset of MS symptoms occurring within 60 days of randomization
• A screening MRI scan with 2 or more T2 lesions at least 3 mm in diameter that are characteristic of MS

Exclusion Criteria:

• Patients with clinically relevant cardiovascular, hepatic, neurological, endocrine or other major systemic disease
• Patients with significantly impaired bone marrow function
• Pregnant or nursing women
• Alcohol or drug abuse
• Use of cladribine, mitoxantrone, or other immunosuppressant agents such as azathioprine, cyclophosphamide, cyclosporin, methotrexate or mycophenolate before enrollment
• Any known condition or circumstance that would prevent in the investigator's opinion compliance or completion of the study

The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.