BTLA and extranodal nasal NK/T cell lymphoma: Many other immune checkpoint molecules, including transforming growth factor-β1 (TGF-β1), cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), T-cell immunoglobulin-3 (TIM-3), T-cell immunoglobulin and ITIM domain (TIGIT), B/T lymphocyte attenuator (BTLA), and lymphocyte-activation gene 3 (LAG-3), are upregulated in NKTCL patients [64, 65].