PDCD1 and central nervous system cancer: To evaluate the ability of cyclin G2 to induce tumors to initiate PD-1 blockade and to better mimic the TME in glioma, we used GL261 cells stably expressing cyclin G2 (herein GL261-OE) and empty vector (herein GL261-EV) to inoculate C57BL/6 WT mice (Fig. 5a).