BTLA and neoplasm: Although tumor cells express numerous antigens, tumor evades T-cell responses and host immunity through negative regulators of the immune system, such as programmed death-1 (PD-1), programmed cell death-ligand-1 (PD-L1)/programmed cell death-ligand-2 (PD-L2), cytotoxic T lymphocyte antigen 4 (CTLA-4), T-cell immunoglobulin mucin 3 (TIM3), 2B4, the B and T lymphocyte attenuator (BTLA), and lymphocyte-activation gene 3 (LAG3) [10-12].