PDCD1 and neoplasm: Further analysis of bulk RNA-seq data from sorted Treg cells of B16 tumors or spleens27 confirmed high expression of Il23r in tumor-infiltrating Treg cells, which was accompanied by an induction of key eTreg genes, such as Pdcd1 (encoding PD-1), Tnfrsf9 (encoding 4-1BB), Icos and Lag3 (Fig. 1h).