TFPI2 and central nervous system cancer: On the one hand, factors secreted by GSCs, such as TFPI2 [31] and OLFML3 [43], actively recruit microglia to the tumor site and induce an immunosuppressive phenotype in microglia; on the other hand, microglia in tumors lead to the formation of an immunosuppressive glioma microenvironment by inhibiting antigen presentation to T lymphocytes [44], synthesizing the immunosuppressive cytokine IL-10 [12], and expressing the immune checkpoint molecules PD-L1/2, CLE2D and CD80/86 [9].