PVR and neoplasm: TIGIT is expressed on activated T cells, a subset of Treg cells and Tfh cells, and NK cells.90,104–107 TIGIT signals via two ligands, CD155 (PVR) and CD112 (PVRL2), that are expressed on APCs, T cells, and some non-hematopoietic cells.90,106,107 Interestingly, in tumors (murine and human) both immune cells and tumor cells express high levels of TIGIT ligands.