EGFR and glioblastoma: How the aberrant EGFR signaling pathway regulates these T cells in the GBM microenvironment may be related to the expression of some immunosuppressive molecules or cytokines, such as programmed death-ligand 1 (PD-L1) (23), extracellular-5’-nucleotidase (CD73) (49), and transforming growth factor (TGF)-β (50), which will be discussed in detail in the next section.