CD274 and meningioma: Because the pattern of signal detected by RT-PCR in tissues cannot exclude that PD-L1 was expressed in infiltrating immune cells, we performed both RT-PCR (Fig. 2B) and immunoblot analysis (Fig. 2C) on four primary patient derived meningioma cell lines (MG2, 5, 6 and 8; Table S6) to determine if meningioma cells themselves express PD-L1.