LGALS9 and cancer: Recent studies have identified novel immune checkpoint targets such as lymphocyte activation gene 3 (LAG-3), T cell immunoglobulin and ITIM domain (TIGIT), T cell immunoglobulin and mucin-containing domain 3 (TIM-3), hepatitis A virus cellular receptor 2 (HAVCR2) gene and the TIM-3 ligand galectin-9 (Gal-9), etc. Cytotoxic T lymphocyte-associated protein 4 (CTLA-4) expressed by T cells is recognized as a key immune checkpoint for autoimmunity and cancer therapeutic targets.