In vivo induction of CD8⁺T-cell responses by adoptive transfer of DC subsets. (A,C,E) Purified pDCs and cDCs isolated from untreated or CpG-injected 129sv mice were loaded or not with OVA_257-264 peptide (pep) and transferred into syngeneic mice. (B,D,F) Purified pDCs and cDCs isolated from untreated or heat-inactivated influenza virus-injected 129sv mice were loaded or not with GP33_33-41 peptide and transferred into 129sv syngeneic mice. Seven days later, spleen cells were tested for peptide-specific CTL responses (A-B), for the frequency of peptide-specific IFN-γ–producing cells among splenocytes (C-D), and for the IFN-γ concentration in response to OVA_257-264 or GP33_33-41 peptide (E-F). CTL activity was assessed on OVA_257-264 (A) or GP33_33-41 peptide–loaded target cells (B). The percentages of specific lysis presented were obtained for a 30:1 effector-to-target ratio after subtraction of unspecific lysis. (C-D) Frequency of peptide-specific IFN-γ spot-forming cells (sfc's) in spleens was quantified by ELISPOT. (E-F) IFN-γ production was determined in culture supernatants of restimulated splenocytes from immunized mice. Each symbol corresponds to an individual mouse. Results show the cumulative results obtained in 10 independent experiments for OVA-loaded, unstimulated pDCs and in 4 independent experiments for GP33-loaded, unstimulated pDCs and CpG and virus-activated pDCs. Horizontal bars represent medians. Statistical analysis compared the CD8⁺ T-cell responses induced by each DC group to those induced by virus-activated peptide-loaded pDCs. NS indicates not significant.