This is a prospective, randomized, open-label, blinded endpoint (PROBE) design clinical trial, in multiple stroke centers of China. The total sample size will be 98. Patients being treated with standard alteplase bridging and mechanical thrombectomy will be randomly assigned in a 1:1 ratio to receive oral fingolimod or standard care. The primary outcome will be the salvaged ischemic tissue from baseline to day 7. AIS patients with proximal cerebral arterial occlusions will have CT perfusion (CTP) before treatment, and multimodal MRI including diffusion and MR perfusion (MRP) at 24 hours and 7 days after receiving treatment. Clinical outcomes will be assessed using the National Institutes of Health Stroke Scale score (NIHSS) at baseline, day 1 and day 7 and the modified Rankin Scale (mRS) at 90 days. Circulating lymphocyte counts will be monitored with FACS at baseline, day 1 and day 7 to confirm the biological activity of fingolimod.