PDCD1 and glioblastoma: However, GBM cells become able to elicit a series of mechanisms that permit the recruitment of monocytes that become tumor-associated macrophages (TAMs) as well as the recruitment of tumor tolerogenic lymphocytes like T regulatory cells (Tregs) with the production of anti-inflammatory cytokines such as TGF-β, VEFG, and interleukin- (IL-) 6 and 10 [3, 4], besides the expression of immune checkpoint molecules that inhibit cytotoxic immune response, cytotoxic T lymphocyte antigen-4 (CTLA-4), and programmed cell death-1 (PD-1) [5, 6].