Enhanced induction of IFN-γ–secreting TAA-specific T cells when stimulator DCs are transfected with iPsiRNA. (A) DCs generated from 3 HLA-A2⁺ donors were transfected with either CsiRNA or iPsiRNA. After the induction of maturation with CC, these DCs were transfected with RNA encoding the indicated TAA and used to stimulate autologous T cells in vitro. After 2 restimulations with identically prepared DCs, IFN-γ ELISPOT assays were performed using the indicated defined HLA-A2–restricted peptides generated by the cP, the iP, or independently of the identity of the proteasome (Tyr. Leader). ■ indicates the fold increase in the number of peptide-specific ELISPOTs induced by iPsiRNA-transfected DCs versus CsiRNA-transfected DCs; □, the fold increase in nonspecific background ELISPOTS against control peptide for T cells induced by iPsiRNA-transfected versus CsiRNA-transfected DCs. (B) DCs generated from 6 individual HLA-A2⁻ donors were transfected with either CsiRNA or iPsiRNA. After the induction of maturation, these DCs were transfected with RNA encoding the indicated TAA and used to stimulate autologous T cells in vitro. After a single restimulation with identically prepared DCs, IFN-γ ELISPOT assays were performed using autologous DCs transfected with the specific TAA RNA or a negative control RNA as targets. ■ indicates the fold increase in the number of TAA-specific ELISPOTS induced by iPsiRNA-transfected DCs versus CsiRNA-transfected DCs; □, the fold increase in nonspecific background ELISPOTS against control RNA–transfected autologous DC targets for T cells induced by iPsiRNA versus CsiRNA-transfected DCs. Absolute numbers of IFN-γ ELISPOTS for each depicted ratio for each individual donor were compared by t test; *P < .01; ⁺P < .05. Horizontal bars indicate unity.