CD274 and glioma: It involves not only the interaction between PD-1 and PD-L1, but also with a variety of immunosuppressive molecules and cells that work together to shape the immunosuppressive microenvironment of glioma, for example, the polarization state of GAMs, the functional status of TILs, and the number and activity of Tregs all affect the function of the PD-1/PD-L1 axis.