STAT3 signaling is critical for TMZ-induced PD-L1 expression in GBM cells. A, B. U87 and U251 cells were pretreated with 1 μg/ml actinomycin D for 2 h and then challenged with or without TMZ for 24 h. The PD-L1 expression level in GBM cells were determined by FCM. C. U87 cells were treated with 200 μM TMZ for 0-48 h, followed by WB analysis using STAT3pY705, STAT3, HIF-1, c-Myc and Tubulin antibodies. D. U87 cells were pretreated with or without STAT3 inhibitor VI for 1 h and then treated with or without TMZ for 24 h, followed by FCM analysis using PE-conjugated PD-L1 antibody. E. U87 cells which stably express control shRNA (shctrl) or STAT3 shRNA (shSTAT3) were pretreated with or without TMZ for 24 h, followed by FCM quantification with PE-conjugated PD-L1 antibody.