Durability of vaccine-induced T cell responses. (A) Monitoring of the T cell responses in representative volunteers of the two study groups. Only volunteers with positive T cell responses in the IFN-γ ELISPOT assay at week 48 were retested at week 72, which corresponded to 1 yr after the completion of the vaccination regimen. (B) Mean frequencies of IFN-γ–secreting cells/106 blood mononuclear cells at weeks 28, 48, and 72 in the eight volunteers within the DNA C plus NYVAC C group with a positive T cell response at weeks 72, 48, and 28, and mean frequencies of IFN-γ–secreting cells/106 blood mononuclear cells in the two volunteers within the NYVAC C group alone with responses at weeks 48 and 28. (C) Changes in the frequencies of functionally distinct CD4 and CD8 T cell populations over time. The results shown were generated from the determinations in six responders. The functional profile of vaccine-induced CD4 and CD8 T cells was assessed using polychromatic flow cytometry as described in Materials and methods. The functional composition of CD4 and CD8 T cell responses was determined as described in Fig. 5 B. All the possible combinations of the responses are shown on the x axis, whereas the percentage of the functionally distinct CD4 and CD8 T cell populations at weeks 28, 48, and 72 are shown on the y axis.
