Mouse Platelet receptor Gi24(VISTA) is a transmembrane glycoprotein with homology to B7like immune costimulatory molecules. Mature mouse Gi24 contains a 159 amino acid (aa) extracellular domain (ECD) with one V-type Ig-like domain, a 21 aa transmembrane segment, and a 97 aa cytoplasmic domain. VISTA promotes both MT1-MMP expression and the MT1-MMP mediated activation of MMP-2. It supports the differentiation of embryonic stem cells (ESC) and enhances BMP-4 induced signaling in ESC, but it is also down-regulated following BMP-4 exposure. It binds to BMP-4 directly and also associates with the type I BMP receptor Activin RIB/ALK-4. It is expressed on the surface of na?ve CD4+ T cells and regulatory T cells. It is up-regulated in vivo on activated monocytes and dendritic cells. VISTA inhibits CD4+ and CD8+ T cell proliferation and their production of IL-2 and IFN-γ. Its expression on tumor cells attenuates the antitumor immune response and enables more rapid tumor progression.