BTLA (B and T lymphocyte associated) is an inhibitory immune checkpoint receptor that negatively regulates lymphocyte function and immune responses. BTLA functions as a co-inhibitory receptor on T and B cells, suppressing immune activation through multiple mechanisms 12. The protein inhibits T cell activation, proliferation, and cytokine production while promoting apoptosis through activation of the PI3K-Akt pathway 3. BTLA serves as a key mediator of immune checkpoint pathways alongside PD-1, utilizing phosphatases SHP-1 and SHP-2 for signal transduction 4. In cancer contexts, BTLA expression correlates with immune infiltration across 33 cancer types and influences survival prognosis in 8 cancer types, suggesting its role as both a prognostic marker and therapeutic target 5. Elevated BTLA levels are associated with T cell exhaustion and increased infection susceptibility in acute-on-chr3 liver failure, where it contributes to disease severity and mortality 3. BTLA represents a promising target for immune checkpoint blockade therapy, with neutralizing antibodies showing therapeutic potential in preclinical models 367. Its expression changes inconsistently following chemotherapy, with increased levels observed in some breast cancer contexts 8.