CD274 and Autoimmunity: The interaction between the programmed death receptor-1 (PD-1/CD279) on immune cells and its ligand, programmed death ligand-1 (PD-L1/B7-DC/CD274) on host cells, results in the suppression of the immune response, including T cell activation and proliferation, leading to escape of host cells from autoimmunity and resistance to HER2-targeted drugs [71].