The STem Cell-derived Extracellular Vesicle Therapy In Acute Ischemic Stroke (STEVIA)

Inclusion Criteria: * Adults with 19 years or older * Patients within 5 days of symptom onset who have not received thrombolytic therapy or undergone endovascular reperfusion procedures. * Patients within 5 days of symptom onset who have received thrombolytic therapy or undergone endovascular reperfusion procedures but show no clinical recovery after 2 days of observation. * Imaging findings must meet both of the following: * Infarction within the middle cerebral artery territory on diffusion-weighted imaging (DWI) * Infarct size ≥ 20 mm in the longest diameter on DWI * Neurological status meeting all three of the following NIHSS criteria: * Moderate to severe neurological deficit (NIHSS score between 5-21) * New onset of motor weakness (score 2-4 in at least one of NIHSS items 5a, 5b, 6a, or 6b) * No impaired consciousness (score 0-1 on NIHSS items 1a, 1b, and 1c) * Voluntary written informed consent Exclusion Criteria: Subjects are ineligible if they meet any of the following: * Pre-stroke disability (pre-stroke mRS ≥ 2) * Likely to recover spontaneously, based on all three of: * No longer meeting the NIHSS inclusion criteria 48 hours post-thrombolysis or endovascular therapy * Lacunar stroke due to small vessel occlusion * SAFE (Shoulder Abduction and Finger Extension) score ≥ 5 * Presence or risk of malignant middle cerebral artery infarction with brain edema * Significant medical history within the past 5 years: * Severe heart failure * Severe infectious disease * Severe hepatic failure or renal failure * Newly diagnosed or actively treated cancer * Any systemic disease deemed by investigator to significantly reduce life expectancy * Any condition likely to hinder follow-up during the study * Diagnosed severe psychiatric illness: * Moderate or greater depression pre-stroke with functional impairment and suicide risk * Pre-stroke dementia interfering with daily living (CDR ≥ 2) * Contraindication to MRI (e.g., pacemaker) * Pregnant or breastfeeding, or unwilling to use effective contraception method for 90 days after last dose. * Participation in another clinical trial within the past 3 months * Any other reason determined by the investigator that would prevent participation