David A Reardon [31] discovered that combination therapy of anti-CTLA-4 plus anti-PD-1 resulted in changes of immune landscape that the proportion of activated CD8+ cells as well as natural killer cells increased and suppressive immune cells decreased in the tumor microenvironment, which achieved the therapeutic effect and prolonged tumor-free survival in murine glioblastoma model. Here, PDCD1 is linked to glioblastoma.