The expanding repertoire of targets for immune checkpoint inhibition in bladder cancer: What lies beneath the tip of the iceberg, PD-L1

Over the last decade, a new understanding of tumor-immune system interplay has been ushered in, lead in large part by the discovery of immune checkpoints mediated through B7-CD28 family interactions. Therapeutic blockade of the PD-L1 immune checkpoint pathway has already shown great success as a cancer immunotherapy for advanced urothelial carcinoma, leading to durable clinical remissions in an otherwise incurable disease. There are newly described members of the B7-CD28 family including B7-H3, B7x, and HHLA2. These ligands are thought to play an essential role in suppressing T-cell response, leading to immune tolerance of tumors. This feature makes them attractive targets for novel immunotherapy treatment paradigms. Here, we review the literature of current strategies and future directions of immune checkpoint blockade therapy for bladder cancer.