Inclusion Criteria- Clinical diagnosis of supratentorial acute ischemic stroke defined by LKN ≤24 hours prior to study treatment initiation.
- Score of 5 to 23 points, inclusive, on the NIHSS at Screening for subjects initiating treatment ≤9 hours from LKN. Note: NIHSS eligibility must be confirmed within 60 minutes prior to randomization.
- Score of 5 to 15 points, inclusive, on the NIHSS at Screening for subjects initiating treatment >9 to ≤24 hours from LKN. Note: NIHSS eligibility must be confirmed within 60 minutes prior to randomization.
- Prior to index stroke, patient was able to perform basic activities of daily living without assistance: dressing, eating, walking, bathing, and using the toilet.
- For those subjects who underwent a cranial MRI, there is at least 1 acute infarct with a diameter of ≥2 cm on baseline brain diffusion-weighted imaging.
Exclusion Criteria- Lacunar or isolated brainstem or cerebellar stroke based on clinical assessment and available acute imaging studies performed under the standard of care.
- Presence of acute intracranial hemorrhage on acute brain CT or MRI. However, petechial hemorrhages of ≤1 cm are not exclusionary.
- Severe stroke defined by imaging criteria based on either one of the following:
- Alberta Stroke Program Early CT (ASPECT) score of 0 to 4 based on head CT or
- Acute infarct volume on MRI diffusion weighed imaging greater than or equal to 70 mL
- Seizure at the onset of stroke.
- Known history of prior treatment with natalizumab.
- Known history of active viral hepatitis B or C.
- Signs and symptoms of active or acute infection.
NOTE: Other protocol-defined inclusion/exclusion criteria may apply.