Sponsor decision to withdraw study at this time.

Phase IV, proof-of-concept, randomized, open-label, multi-center, two-arm, 9-month study to evaluate the neuroprotective effects of Natalizumab (TYSABRI®) or Interferon beta-1a (AVONEX®) treatments initiated at the time of acute optic neuritis (AON) as measured by RNFL thickness from Optical Coherence Tomography in patients with Relapsing Remitting Multiple Sclerosis (RRMS).

Inclusion Criteria:

• Diagnosis of RRMS.
• Patients with unilateral AON consistent with Multiple Sclerosis (MS).
• Treatment with intravenous methylprednisolone (IVMP) at 1gm daily for three days after the onset of AON, without a taper, and completed within 14 days of the AON symptom onset.
• Age 18-55 years.
• Expanded Disability Status Scale (EDSS) 0 to 5.0.
• Understand and sign informed consent.

Exclusion Criteria:

• History or presence of progressive multifocal leukoencephalopathy (PML).
• Diagnosis of Primary Progressive Multiple Sclerosis (PPMS) or Secondary Progressive Multiple Sclerosis (SPMS).
• Immune-compromised in the judgment of the Investigator.
• History of or presence of clinically significant medical illness or laboratory abnormality that, in the opinion of the investigator or Sponsor, would preclude participation in the study.
• Concomitant ophthalmologic disorders (e.g. diabetes, macular degeneration, etc).
• Previous history of severe disc edema, hemorrhage, or > 1 confirmed optic neuritis (ON) with the most recent ON symptom onset being less than 12 months ago.
• Previous treatment with > 1 Disease Modifying Therapy (DMT).
• Previous treatment with investigational products for MS, immunosuppressant or cytotoxic therapy.
• Previous treatment with TYSABRI®
• Women who are not postmenopausal, surgically sterile, or willing to practice contraception.
• Women pregnant, breast feeding, or planning to become pregnant.
• Involved with other study protocol simultaneously without prior approval.
• Determined not suitable for study participation by Investigator and/or Sponsor.