TIM-3, an immunoregulatory checkpoint receptor expressed on a subset of T cells (including exhausted and regulatory T cells), natural killer (NK) cells, monocytes, and dendritic cells. TIM-3 has multiple ligands, including galectin-9, CEACAM1, HMGB1, and phosphatidylserine. In the tumor microenvironment, the engagement of TIM-3 by its ligands (e.g., galectin-9 expressed by tumor or stromal cells) transmits an inhibitory signal that suppresses T-cell activation, cytokine production, and cytotoxic function, contributing to T-cell exhaustion and immune evasion.