PDCD1 and glioblastoma: GBM immune evasion mechanisms include: (I) downregulation of MHC-I molecules on tumor and antigen-presenting cells, limiting immune recognition; (II) activation of immune checkpoints like CTLA-4, PD-1/PD-L1, and LAG-3, suppressing immune responses; (III) secretion of immunosuppressive biomolecules such as TGF-β, IL-10, prostaglandin E2, and VEGF, creating a suppressive cytokine milieu; and (IV) infiltration of immunosuppressive cells like Tregs, M2-polarized tumor-associated macrophages (TAMs), and MDSCs, enhancing immunosuppression (33).