PDCD1 and glioblastoma: LRRC4 inhibited the infiltration of Ti-Treg cells, promoted the expansion of Ti-Teff cells and CD4+CCR4+ T cells, and enhanced the chemotaxis of CD4+CCR4+ T cells in the GBM microenvironment by promoting cytokine secretion and affecting GBM cell-derived exosomes (cytokine-free and PD-1-containing).