PDCD1 and neoplasm: Previous studies have highlighted that CD8+ T cells in the tumor microenvironment frequently manifest a state of exhaustion, characterized by diminished effector functions, including reduced cytokine production such as IL-2 and IFN-γ 35 and the upregulation of co-inhibitory molecules on the cell surface, notably PD-1, T cell immunoglobulin and mucin domain-containing protein 3 (Tim-3), and Lag-3 36.