APC and neoplasm: We found that PD-1 blockage further reduced the tumor number (Isotype/Lgr5/Apc: 79.8 ± 15.4; PD1/Lgr5/Apc: 65.1 ± 18.2; Isotype/Lgr5/Arf1/Apc: 32.7 ± 12.3; PD1/Lgr5/Arf1/Apc: 20.4 ± 9.9) and increased the lifespan but did not affect the body weight of Lgr5/Arf1/Apc mice (Fig. 7h, and Supplementary Fig. 15a, b), indicating that Arf1 ablation and PD-1 blockage had a synergistic effect.