TAGAP (T cell activation RhoGTPase activating protein) is a GTPase-activating protein specifically expressed in activated T cells that plays critical roles in T cell function and immune regulation 1. Mechanistically, TAGAP functions as a RhoA-specific GAP that interacts with RhoH, an adapter protein in proximal T cell receptor (TCR) signaling 1. By competing with ZAP70 for RhoH binding, TAGAP inhibits excessive TCR signal transduction, thereby permitting appropriate Th17 cell differentiation 1. Additionally, TAGAP influences CD4+ T cell function through the JAK-STAT signaling pathway, enhancing cytotoxicity and promoting pro-inflammatory cytokine production 2. TAGAP polymorphisms are associated with multiple autoimmune diseases, including celiac disease, Crohn's disease, rheumatoid arthritis, multiple sclerosis, and psoriasis 31. The rs1738074 variant carries a 1.17-fold increased risk for celiac disease 4. In lung squamous carcinoma, reduced TAGAP expression correlates with immunosuppression; TAGAP overexpression enhances CD4+ T cell anti-tumor responses and inhibits tumor growth via c-Rel pathway suppression 5. These findings establish TAGAP as a potential therapeutic target for modulating immune responses in autoimmune diseases and cancer immunotherapy.