Immunizations with recombinant lentivectors elicit longer-lived Melan-A–specific CD8⁺ T-cell responses than peptide immunizations. (A) A2/K^b mice were immunized either with recombinant lentivectors encoding Melan-A_26-35 (A27L) (rec.lv/M-A_26-35), left panel, or with peptides Melan-A_26-35 (A27L) in adjuvant (adj/M-A_26-35), right panel. At the indicated time points after immunization, the frequency of Melan-A–specific CD8⁺ T cells (Tet⁺) was measured ex vivo by staining peripheral blood cells with Melan-A_26-35/A2K^b tetramers. Each symbol represents an individual mouse. Note that, in the case of adjuvant/Melan-A_26-35 immunizations, 2 mice at day 54 and 3 mice at day 60 showed a frequency of Tet⁺CD8⁺ T cells below the detection limit. Graphs represent the pool of 5 independent experiments. The black line connects mean values obtained at the indicated time points. *P < .05. (B) The expression of CD62L and CD127 (IL-7Rα) on Tet⁻ and Tet⁺CD8⁺ T cells at the peak of the response (day 18 and day 7 for recombinant lentivector/Melan-A_26-35 and for adjuvant/Melan-A_26-35 immunizations, respectively) is shown for one representative experiment. (C) Bar graphs represent the percentage of CD127^hi cells among Tet⁺CD8⁺ T cells at the indicated time points after immunization with recombinant lentivector/Melan-A_26-35 (top panel) and with adjuvant/Melan-A_26-35 (bottom panel). Error bars represent SD (n = 5). *P < .05.