VSIR, V-Set Immunoregulatory Receptor, also known as VISTA, is an immunoregulatory receptor that inhibits the T-cell response. It may promote differentiation of embryonic stem cells, by inhibiting BMP4 signaling. VSIR, or V-set immunoregulatory receptor, could be involved in the pathogenesis of chronic rhinosinusitis with nasal polyps. V-domain Immunoglobulin Suppressor of T cell Activation (VISTA) is an inhibitory immune-checkpoint molecule that suppresses CD4+ and CD8+ T cell activation when expressed on antigen-presenting cells. VSIR is broadly expressed in the spleen, bone marrow, and other tissues. Diseases associated with VSIR include Ichthyosis, Congenital, Autosomal Recessive 6, and Monckeberg Arteriosclerosis.