V-domain Ig-containing suppressor of T cell activation (VISTA), also known as PD-1H, is a member of the immunoglobulin (Ig) superfamily, whose extracellular domain bears homology to the B7 family ligand, particularly PDL1. VISTA is predominantly expressed on granulocytic, myeloid cells and T cells.15 VISTA expresses on T cells as a part of an inhibitory immune checkpoint that suppresses T cell activation, proliferation, and cytokine production.16 Recently, a number of research studies have reported the expression of VISTA in solid tumors such as melanoma, lung, pancreas and colorectal, these studies found that VISTA may act as an important biomarker in solid tumors.15,17
In both normal and malignant tissue, VISTA is expressed abundantly in vascular endothelial cells (noted as vasculature). Additionally, VISTA is typically expressed in quiescent naive T-Cells and monocytes and promotes quiescence in surrounding immune cells. Activated T-cells are reported to express less VISTA than quiescent cells.18 In our evaluation, tumor cells expressing VISTA were rare, however the tumor micro-environment showed a high prevalence of mixed-strength VISTA expression in vasculature, tumor infiltrating lymphocytes, and other tumors cells including but not limited to fibroblasts.