PDCD1 and nonpapillary renal cell carcinoma: Notably, the expression levels of these latter four genes encoding non-PD-1/CTLA-4 checkpoint ligands were substantially higher than abundance of the PD-1 ligand PDCD1LG2 and the CTLA-4 ligand CD80. To corroborate these data at the protein level we interrogated the CPTAC database of proteomic analyses of normal and human ccRCC samples27.