PDCD1 and neoplasm: To investigate whether tumor-extrinsic factors contribute to the improved anti–PD-1 response in Ptdss1 KD tumors, we transplanted KD or WT cells in mice, treated the mice with anti–PD-1 or PBS 3- and 6-days postinoculation, and profiled the immune subsets within the TME on day 9 by single-cell RNA sequencing (scRNAseq).