PDCD1 and neoplasm: There was no difference in tumor growth between WT mice implanted with MC17-51 tumor cells alone and recipients of monocytes from tumor-bearing Pdcd1f/f mice, whereas recipients of monocytes from tumor-bearing Pdcd1f/fLysMCre mice had substantially reduced tumor growth (Fig. 8a,b), indicating that PD-1-deficient monocytes could mediate tumor control.