CD274 and neoplasm: A study in metastatic melanoma models showed that cytotoxic T cells near the tumor edge and macrophages had the most obvious exhaustion, and macrophages near the tumor edge and near cytotoxic T cells also expressed more PD-L1 [53].The greatest exhaustion of cytotoxic T cells occurs in the area of the macrophage barrier, where macrophages are abundant and have more opportunity to come into contact with T cells within the “effective interaction distance” (considered by most studies to be the effective interaction distance within a radius of less than 20 μm).