CEACAM1 and neoplasm: The precise binding site for Gal-9 on TIM-3 has not been clearly defined, and its interaction suppresses immune responses.55 Recently, it was reported that Gal-9 regulates TIM-3 cell surface clustering, which is necessary for the suppressive function of TIM-3.56 As the most recently discovered ligand, CEACAM1, which is highly expressed by some tumor cells, plays a role in dampening T cell responses.57 58 As a functional TIM-3 ligand,59 PtdSer is an essential component of bilayer cell membranes and is normally present in the inner leaflet.