CD8A and breast carcinoma: To examine whether TWIST1-upregulated CD274/PD-L1 expression in breast cancer cells promotes immune evasion, we established a coculture system consisting of breast cancer cells with the expression of ovalbumin (OVA), a tumor antigen mimic, and CD8+ T cells isolated from OT-1 mice that express an OVA-specific T-cell receptor [54].