IFNG and glioblastoma: PD-L1 can be constitutively expressed on the surface of GBM cells through oncogenic signaling14 or alternatively expressed in response to immune-stimulating cytokines such as IFNγ, a mechanism called adaptive immune resistance.15 Topalian et al.7 showed that anti-PD-1 therapies are most likely unsuccessful in tumors without PD-L1 expression.