PDCD1 and neoplasm: To evaluate whether 2L4-8 enhances the efficacy of anti-PD-1, E0771 breast tumor-bearing mice (tumor volume ~50 mm3) were randomly divided into four groups: isotype control (CTRL), 2L4-8 monotherapy, anti-PD-1 monotherapy, and anti-PD-1 combined with 2L4-8 (Combo).