CTLA4 and glioblastoma: Cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) stimulates negative costimulatory signaling on the activated T cells,176 supporting an immunosuppressive environment by inducing immune tolerance.177 Currently, the CTLA-4 blocker ipilimumab is being assessed in GBM (NCT04323046, NCT04396860, and NCT04817254).