Natarajan et al. injected a 64Cu-labeled anti-mouse PD-1 Ab in Foxp3+ LuciDTR4 mice, a mouse model that contains high expressing PD-1 Foxp3+ regulatory T cells, bearing B16-F10 tumors, to detect PD-1 expressing tumor infiltrating lymphocytes (TILs) (Natarajan et al. 2015). This evidence concerns the gene PDCD1 and neoplasm.