CD155 (also known as PVR, Tage4, Necl-5) has the highest affinity for TIGIT and is expressed on various types of cells, such as antigen-presenting cells (APCs), epithelial cells, fibroblasts, endothelial cells (in physiological conditions and tumors), T cells, B cells, and fibroblasts, and is upregulated by DNA damage in viral infections and during cancer [20,44,69]. This evidence concerns the gene PVR and viral infectious disease.