CD274 and chronic obstructive pulmonary disease: From the perspective of adaptive immunity, COPD pulmonary inflammation affects the ability of CD8+ cells to clear tumor cells, and impacts the balance of Th1/Th2, the proportion of regulatory T cells and Th17 cells, and the expression of programmed cell death protein 1 (PD-1) and its ligand (PD-L1) in CD8+ T cells, resulting in cell cycle arrest and T cell inactivity [33].