TIM-3: An update on immunotherapy.

T cell immunoglobulin and mucin domain 3 (TIM-3) was originally found to be expressed on the surface of Th1 cells, acting as a negative regulator and binding to the ligand galectin-9 to mediate Th1 cell the apoptosis. Recent studies have shown that TIM-3 is also expressed on other immune cells, such as macrophages, dendritic cells, and monocytes. In addition, TIM-3 ligands also include Psdter, High Mobility Group Box 1 (HMGB1) and Carcinoembryonic antigen associated cell adhesion molecules (Ceacam-1), which have different effects upon biding to different ligands on immune cells. Studies have shown that TIM-3 plays an important role in autoimmune diseases, chronic viral infections and tumors. A large amount of experimental data supports TIM-3 as an immune checkpoint, and targeting TIM-3 is a promising treatment method in current immunotherapy, especially the new combination of other immune checkpoint blockers. In this review, we summarize the role of TIM-3 in different diseases and its possible signaling pathway mechanisms, providing new insights for better breakthrough immunotherapy.