CTLA4 and neoplasm: Immune checkpoint proteins—especially PD-1, PD-L1, cytotoxic T lymphocyte-associated protein 4 (CTLA-4), and B7 homolog 3 (B7-H3) —have immunosuppressive characteristics that are up-regulated in the GBM TME, which contribute to tumor cell immune escape (Berghoff et al., 2015; Nduom et al., 2016; Saha et al., 2017; Wang et al., 2018).