Proof-of concept clinical trials have indicated that the sphingosine-1-phosphate receptor modulator fingolimod may be efficacious in attenuating brain inflammation and improving clinical outcomes in patients with AIS as a single therapy beyond 4.5 hours of disease onset, or in combination with alteplase within 4.5 hours of disease onset. So in this study the investigators try to determine whether the addition of fingolimod, administered within 6 hours after the onset of symptoms in patients receiving alteplase bridging with mechanical thrombectomy, improves radiologic and clinical outcomes.