To determine how NDV affected PD-1 expression on tumor-resident T cells, 2.5 × 105 B16-F10 cells and 5 × 105 CT26LacZ cells were implanted intradermally and subcutaneously, respectively, and when tumors reached 5 mm × 5 mm, 5 × 107 PFU of NDV-GFP was intratumorally injected every other day for a total of three injections. This evidence concerns the gene PDCD1 and neoplasm.