Abstract
Increased expression of the B7 family of immune checkpoint proteins hinders tumor elimination by the immune system. Expression levels of the B7-H5 protein were found to be upregulated in clear cell renal cell carcinomas (ccRCC). We here report the molecular, functional, and clinical characterization of B7-H5 from renal cancer cells and metastatic ccRCC tumors. B7-H5 was highly glycosylated and mainly expressed in the cell membrane. Mutagenic studies on B7-H5 identified the residues targeted by N-glycosylation and revealed an impact of B7-H5 glycosylation on protein expression levels and localization. B7-H5 knockdown decreased the cell proliferation and viability of renal cancer cells. We analyzed B7-H5 expression on tumor cells and tumor-infiltrated leukocytes (TILs) in samples from metastatic ccRCC patients and found that B7-H5 expression on TILs correlated with syncronous metastases and poor outcomes. These results provide insights into the molecular properties and clinical impact of B7-H5 and support B7-H5 as a new immunotherapeutic target in metastatic ccRCC.