“…Specifically, it is well known that the brain tumor microenvironment is characterized by secretion of a variety of anti-inflammatory molecules, not only by tumor cells themselves, but also by other surrounding peritumoral cells previously conditioned by the tumor. These peritumoral cells are peripheral immune cells (i.e., tumor-associated macrophages (TAMs), T cells, myeloid-derived suppressor cells (MDSC) and T regulatory cells (Tregs)), and various specialized organ-resident cells including microglial cells, astrocytes and perivascular pericytes (PC) [8,10,13]. Collectively, anti-tumor innate and adaptive immune responses in the tumor microenvironment are altered, and several mechanisms including decreased T cell activation and proliferation, induction of anergic T cells, differentiation of Tregs, down-regulation of major histocompatibility complex (MHC) expression and polarization of macrophages to an immunosuppressive M2 phenotype, are prompted by tumor cells [22,26].…”