Activated T cells at the tumor site express multiple checkpoint (co-inhibitory) molecules including cytotoxic T-lymphocyte associated protein-4 (CTLA4), programmed cell death 1 (PD-1), lymphocyte-activation gene 3 (Lag3), T cell immunoglobulin mucin 3 (TIM3), and B and T lymphocyte attenuator (BTLA). Here, PDCD1 is linked to neoplasm.