To gain more insight into the association between IGFBP3 and PD-L1 in GBM, we added varying concentrations of exogenous IGFBP3 to U251 and U118 cells for 24 h, which lowly express endogenous IGFBP3 (Additional file 3: Fig. S1A). The gene discussed is IGFBP3; the disease is glioblastoma.