PD-1 KO mice were more resistant to AML. B6 PD-1 KO and B6 WT mice were injected intravenously with 10⁶ C1498FFDsR cells. Mice (8-10 mice/group) were monitored using BLI, analyzed for survival, or killed (3 or 4 mice/group) at 25 days after AML injection for immune parameter determination. (A) B6 PD-1 KO versus WT mice had much lower tumor burdens (A) and significantly prolonged survival time (B) compared with WT mice (C). The number of Foxp3⁺ Tregs per liver in WT naive mice was significantly lower than in mice with AML. The total number of Tregs in naive PD-1 KO mice was significantly higher than WT mice and did not further increase by AML challenge. (D) The ratio of CD8⁺ T cells to Tregs was significantly reduced in AML-bearing WT versus naive WT mice, whereas the CD8⁺ T cell-to-Treg ratio was significantly higher in naive PD-1 KO versus WT mice because of a proportionately higher number of CD8⁺ T cells in PD-1 KO versus WT mice (data not shown). Challenging PD-1 KO with AML did not significantly alter this ratio. Results from one of 3 representative experiments are shown. Bar graphs represent mean ± SD.