CTLA4 and neoplasm: Within the GBM tumors, there are distinct immunoregulatory macrophages, including spalt-like 1-positive (Sall1+) tumor microglia and Sall1-monocyte-derived macrophages, as well as immunosuppressive T-regulatory cells and dysfunctional T-cell populations, characterized by high levels of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 [21].