This study is a randomized, double-blind, placebo-controlled clinical trial. Investigators aim to assess the efficacy and safety of interleukin-6 receptor inhibitor combined with endovascular treatment in patients with acute anterior circulation large vessel occlusion stroke.

The study population are patients with acute anterior circulation large vessel occlusion stroke and planned to undergo endovascular treatment. All participants are randomly assigned in a 1:1 ratio to the tocilizumab group or the placebo group. In tocilizumab group, participants will receive tocilizumab combined endovascular treatment. And in placebo group, participants will receive placebo combined endovascular treatment. All participants will be visited immediately postoperatively, at 24 hours, 7 days, and 90 days after randomization.

Inclusion Criteria:

1. Age 18 years or greater, male or female;
2. Acute ischemic stroke caused by occlusion of intracranial segment of the internal carotid artery, middle cerebral artery M1 or proximal/dominant M2 segment;
3. Decided to undergo emergency endovascular treatment;
4. Time from stroke onset to arterial puncture within 24 hours;
5. National Institutes of Health Stroke Scale (NIHSS) score ≥ 6;
6. Signed informed consent from the patients or the legally authorized representatives.

Exclusion Criteria:

1. Intracerebral hemorrhage, epidural hematoma, subdural hematoma, intraventricular hemorrhage, or subarachnoid hemorrhage;
2. Pre-stroke modified Rankin scale (mRS) score >1;
3. Known allergy to tocilizumab or excipients;
4. Known allergy to iodinated contrast agents;
5. Anticipated difficulty in completing endovascular treatment due to vascular tortuosity;
6. History of congenital or acquired bleeding disorders, coagulation factor deficiency diseases, or thrombocytopenic diseases;
7. Systolic blood pressure ≥180mmHg or diastolic blood pressure ≥110mmHg despite blood pressure control;
8. Neutrophils <2×109 /L;
9. Platelets <100×109 /L;
10. Blood glucose <2.8mmol/L (50 mg/dL) or >22.2mmol/L (400 mg/dL);
11. Serum alanine aminotransferase (ALT) or aspartate aminotransferase (AST) levels >2 times the upper limit of normal;
12. Known recent or current serum creatinine >2 times the upper limit of normal or estimated glomerular filtration rate (eGFR) <60 mL/min;
13. Pregnant, lactating, or planning pregnancy within 90 days;
14. Severe mental disorders or inability to comply with informed consent and follow-up requirements due to dementia;
15. Concurrent malignant tumors or severe systemic diseases with expected survival of less than 90 days;
16. Presence of autoimmune diseases or use of immunosuppressive drugs;
17. Systemic infectious diseases;
18. Participation in another interventional clinical study within 30 days before randomization or currently participating in another interventional clinical study;
19. Considered by the investigator to have other conditions that might affect compliance or preclude participation in this study.

Related data will be shared if full study protocol and statistical analysis plan are provided with reasonable design.