FOXP3 and neoplasm: Lastly, among all of the tumor-infiltrating immune cell subsets, only Foxp3+/PD-1− Treg cells were elevated (Figure 3), a subset known to be more immunosuppressive than Foxp3+/PD-1+ Treg cells [35] and a phenotype expected to be intrinsically insensitive to anti-PD-1 mAb.