PDCD1 and neoplasm: Loss of PTDSS1 also increased the frequency of an iNOS+ (encoded by Nos2) myeloid cell cluster, which were typically observed in mice responding to ICT (44, 45), and induction of this iNOS+ myeloid cell cluster by anti–PD-1 and PTDSS1 deficiency in tumor cells was synergistic (Fig. 5F).