CD274 and Autoimmunity: Under normal physiological conditions, the binding of PD-1 and PD-L1 can down-regulate the activity of T cells and prevent additional damage of cytotoxic effector molecule and autoimmunity, so it is called immune checkpoint (30) A Study confirmed that tumor cells often express negative costimulatory signals such as PD-L1, leading to the failure activation of T cell activation.