Expansion of antigen-specific T cells by DCs is impaired by CYTIP silencing. Mature HLA A2.1⁺ DCs were cocultured with autologous CD8⁺ T cells for 7 days. T cells were stained with anti-CD8-FITC and PE-labeled pentamers specific for HLA A2.1 loaded with EBV peptide. Percentage of CD8⁺/Pentamer⁺ cells are shown. (A) DCs silenced for CYTIP (simDC) or not (mDC) were loaded with EBV peptide and mixed with unloaded CYTIP-silenced DCs or unloaded untreated DCs, respectively, at a ratio of 1:10. The results of 4 independent experiments show that simDCs have a clearly reduced capacity to prime T cells as compared with mDCs in the assay where only 1/10 of DCs is antigen loaded. The P value from a paired Student t test performed with the results of the 4 experiments is .02 (significant). (B) All DCs were loaded with the EBV peptide. simDCs and mDCs exert similar priming activity if all DCs are loaded with antigen. P = .09 (not significant). (C) The bar graphs show the priming capacity of DCs in the setting described in panel A (bar 1, mDCs; bar 2, simDCs) and, in addition, of DCs silenced for CYTIP and loaded with EBV peptide and mixed with 9 parts of untreated unpulsed DCs (setting 3, bar 3) and of untreated DCs loaded with EBV peptide and mixed with 9 parts unloaded CYTIP silenced DCs (setting 4, bar 4). Although 9 parts of unpulsed untreated DCs do not interfere with the priming capacity of loaded silenced DC (bar 3), CYTIP silencing of 9 parts of unloaded DCs impairs priming (bar 4).