This is an investigator-initiated phase III clinical trial employing a randomized, double-blind, placebo-controlled design. The primary objective of this study is to investigate the efficacy and safety of an interleukin-6 inhibitor (tocilizumab) combined with endovascular therapy in patients with acute posterior circulation large-vessel occlusion stroke.

This is an investigator-initiated, prospective, multicenter phase III clinical trial. This trial aims to investigate whether tocilizumab could further improve prognosis for patients with acute posterior circulation large-vessel occlusion stroke receiving endovascular therapy.

Inclusion Criteria:

1. Age 18 years or older, of either sex;
2. Acute ischemic stroke caused by occlusion of the basilar artery;
3. Decide to undergo emergency endovascular treatment;
4. Time from stroke onset to groin puncture within 24 hours;
5. National Institutes of Health Stroke Scale (NIHSS) ≥ 10;
6. Posterior circulation Alberta Stroke Program Early computed tomography score (pc-ASPECTS) ≥ 6;
7. 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 ≥180 mmHg or diastolic blood pressure ≥110 mmHg despite blood pressure control;
8. Neutrophils < 2 × 10^9 /L;
9. Platelets < 100 × 10^9 /L;
10. Blood glucose <2.8 mmol/L (50 mg/dL) or >22.2 mmol/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. Any circumstance that, as assessed by the investigators, might result in harm to the patients if study therapy is initiated;
20. Other conditions that the investigator considers 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.