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. Here, CTLA4 is linked to nonpapillary renal cell carcinoma.