VSIR and melanoma: VISTA is a type I transmembrane protein that antagonizes the programmed death-ligands 1 and 2 (PD-L1 and PD-L2); it is produced at high levels in TILs, such as myeloid-derived suppressor cells and Tregs and its blockade with an antibody results in delayed tumor growth in mouse models of melanoma [60] and squamous cell carcinoma [61].