Presentation of MUC1-derived HLA-A*02–binding T-cell epitopes is sensitive to the proteasome inhibitor lactacystin. Autologous monocyte-derived DCs generated from an HLA-A*02–positive donor were electroporated with MUC1 RNA alone (♦) or additionally incubated with lactacystin (▴). These cells were used as target cells in a standard 51Cr-release assay. M1.1-specific CTLs (A) and M1.2-specific CTLs (B) do not lyse lactacystin-treated MUC1 RNA-transfected DCs. Lysis of the targets can be reestablished by additionally pulsing these DCs with the cognate synthetic peptide M1.1 (A, ▪) or M1.2 (B, ▪). DCs electroporated with irrelevant EGFP RNA (×) were used as control.