CTLA4 and meningioma: Other checkpoint proteins expressed include PD-L2 and B7-H3 in meningiomas with alterations in the PI3K/AKT/mTOR pathway genes [35], CTLA-4 in CD3+ T cells in atypical meningiomas with PIK3CA or smoothened, frizzled class receptor (SMO) mutations [35], and the cancer/testis antigen NY-ESO-1 [36,37].