Inclusion Criteria:  1. Acute ischemic stroke where patient is ineligible for IV thrombolytic treatment with Alteplase due to onset >4.5 hours and is ineligible for endovascular treatment under standard of care due to absence of proximal arterial occlusion (e.g. intracranial ICA, MCA-M1 and dominant M2 segments, and vertebrobasilar arteries).  Dominant M2 segment is defined is a division supplying >50% of the MCA territory vs co-dominant supplying 50% of the MCA territory vs non-dominant supplying <50% of the MCA territory.  2. No significant pre-stroke functional disability (mRS ≤2). 3. Evidence of a disabling deficit including significant aphasia, neglect, hemianopsia, or hemiparesis and/or baseline NIHSS score ≥4 points (obtained prior to randomization).  4. Age ≥18 years (no upper age limit). 5. The presence of a Target Mismatch defined as:  a. Ischemic Core < 50cc) (defined on NCCT/CTP* or DWI-MRI)  e-volume NCCT can be used to exclude patients if the investigator believes that its volume assessment is more reliable than the CTP volume in any particular case.  b. Mismatch Volume (TMax >6sec lesion - Core volume lesion) >10cc c. Mismatch Ratio >1.4 6. Patient treatable within 4.5-12 hours of symptom onset. Symptoms onset is defined as point in time the patient was last seen well (at baseline). Treatment start is defined as initiation of IV TNK or placebo infusion.  7. Informed consent obtained from patient or acceptable patient surrogate.  Exclusion Criteria:  Intracranial hemorrhage (ICH) identified by CT or MRI. Rapidly improving symptoms, particularly if in the judgment of the managing clinician that the improvement is likely to result in the patient having an NIHSS score of < 4 at randomization. Pre-stroke mRS score of ≥ 2 (indicating previous disability) Contra indication to imaging with MR or CT with contrast agents. Infarct core >1/3 MCA territory qualitatively or >50 mL quantitatively (determined by DWI lesion on MR). Participation in any investigational study in the previous 30 days Any terminal illness such that patient would not be expected to survive more than 1 year). Baseline platelet count < 100.000/µL Woman of childbearing potential who is known to be pregnant or who has a positive pregnancy test on admission. Previous stroke within last three months. Recent past history or clinical presentation of ICH, subarachnoid hemorrhage (SAH), arterio-venous (AV) malformation, aneurysm, or cerebral neoplasm other than meningioma. Current use of oral anticoagulants and a prolonged prothrombin time (INR > 1.6). Use of heparin, except for low dose subcutaneous heparin, in the previous 48 hours and a prolonged partial thromboplastin time exceeding the upper limit of the local laboratory normal range Use of glycoprotein IIb - IIIa inhibitors within the past 72 hours. Use of single agent oral platelet inhibitors (clopidogrel or low-dose aspirin) prior to study entry is permitted. Clinically significant hypoglycemia. Uncontrolled hypertension defined by a blood pressure > 185 mmHg systolic or >110 mmHg diastolic on at least 2 separate occasions at least 10 minutes apart, or requiring aggressive treatment to reduce the blood pressure to within these limits. The definition of "aggressive treatment" is left to the discretion of the responsible Investigator. Hereditary or acquired hemorrhagic diathesis. Gastrointestinal or urinary bleeding within the preceding 21 days. Major surgery within the preceding 14 days which poses risk in the opinion of the Investigator. Exposure to a thrombolytic agent within the previous 72 hours. Subject participating in a study involving an investigational drug or device that would impact this study.