PDCD1 and renal cell carcinoma: Although the inhibitory ligands and co-stimulatory receptors did not show apparent differences in Cluster 1 compared to those in Cluster 2, co-inhibitory receptors of tumor-infiltrating immune cells were significantly highly expressed in Cluster 1 compared to those in Cluster 2 or Cluster 3, including BTLA, CTLA4, IL2RA, PDCD1 and so on (Fig. 4E, F), suggesting the existence of infiltration high but immune-suppressive tumor microenvironment in RCC.