IDO-specific T cells boosted specific immunity toward CMV in PBMCs from a healthy donor. PBMCs from an HLA-A2⁺ healthy donor cultured with CMV IE1_316-324 (VLEETSVML) peptide either alone (top) or added an autologous, IDO5 (IDO_199-207; ALLEIASCL)–specific T-cell clone (in a PBMC-to-clone ratio of 2000:1; bottom). The percentage of CMV IE1_316-324–specific CD8⁺ T cells in each culture was identified by flow cytometry with the MHC-tetramer complex HLA-A2/CMV IE1_316-324 and CD8 monoclonal antibody (mAb). For comparison, cells were stained with the MHC-tetramer complex HLA-A2/HIV-1 pol_476-484 and CD8 mAb. Data from 2 representative experiments are shown (A). Percentage of CMV IE1_316-324–specific T cells found in PBMCs cultured alone (□) or added an IDO5-specific T-cell clone (■). Data are mean ± SD (n = 4; P < .05; B). The percentage of CD4⁺CD25^highCD127⁻Foxp3⁺ Tregs in each culture was identified by flow cytometry with intracellular staining for Foxp3. For comparison, cells were stained with isotype controls. The data shown are from 1 donor, representative of 4 experiments (C). Distribution of CD4⁺ and CD8⁺ T cells in the cultures. Data are mean ± SD (n = 4; D).