We found that after tail vein injection of anti-PD-1 antibodies into mice bearing WT or Cdk2-/- cancer cells, the Cdk2-/- tumors plus anti-PD-1 Ab grow slower than Cdk2-/- PBS group (Figures 6C, D), but there was no statistical difference in WT tumors with or without anti-PD-1 Ab treatment (Figures 6C, D). This evidence concerns the gene PDCD1 and cancer.