PDCD1 and gastric neoplasm: Furthermore, gene set enrichment analysis (GSEA) performed by the Molecular Signature Database (MSigDB) was used to identify the potential regulators for immunosuppression in TDLNs and in primary tumors, and PD-1 checkpoint pathway was identified to be one of the most significantly up-regulated pathways (Fig. 2C), suggesting immunosuppression in primary gastric tumors and TDLNs is associated with PD-1 up-regulation.