Age 18 to 80 Years

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

Score of 5 to 15 points, inclusive, on the NIHSS at Screening for subjects initiating treatment >9 to ≤24 hours from LKN

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

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