CD274 and glioblastoma: The combination of PD-1/PD-L1 reduces T cell receptor (TCR) and CD28 signaling, suppressing T cell effector activity and driving the immunosuppressive environment development.168–170 Although GBMs express elevated levels of PD-L1,171 to date, PD-1/PD-L1 immunotherapy trials using GBM have not been fruitful.48 The possible reason for this is that TMZ used in the trial affects PD-L1 level in GBM172,173 and is associated with suppression of immunity by dexamethasone.174,175