Characterization of functional and phenotypic changes in anti-Gag vaccine-induced T cell responses and their role in protection after HIV-1 infection

Abstract

Worldwide HIV-1 vaccine efforts are guided by the principle that HIV-specific T cell responses may provide protection from infection or delay overt disease. However, no clear correlates of T cell-mediated immune protection have been identified. Here, we examine in a HLA-B27(+) HIV seronegative vaccinee persistent HIV-specific vaccine-induced anti-Gag CD4(+) and CD8(+) T cell responses. Although these responses exhibited those characteristics (multifunctionality, appropriate memory phenotype, and targeting of epitopes associated with long-term nonprogression) predicted to correlate with protection from infection, the subject became HIV infected. After HIV infection, the vaccine-induced CD8(+) T cells expanded, but both CD4(+) and CD8(+) T cell responses acquired the functional and phenotypic patterns characteristic of chronic HIV infection. The virus quickly escaped the vaccine-induced T cell response, and the subject progressed more rapidly than expected for someone expressing the HLA-B27 allele. These data suggest that control of HIV by vaccine-elicited HIV-specific T cell responses may be difficult, even when the T cell response has those characteristics predicted to provide optimal protection.

Fig. 2.

Fine characterization of vaccine-induced T lymphocyte functional responses by using nine-color flow cytometry. The two left dot plots of each row represent the unstimulated control, and the two right dot plots show cells stimulated with KK10 peptide (a) or CD8⁺ (b) or CD4⁺ (c) overlapping Gag peptides. The staining combination for each column of dot plots is shown at the bottom of the figure. The pie charts (see Materials and Methods) depict the contribution of various responding CD8⁺ (a and b) or CD4⁺ (c) T cell populations (background adjusted).

Fig. 4.

Shift in T cell functional profile in 202-T07 after infection. The pie charts (see Materials and Methods) depict the background-adjusted T cell functional response to the KK10 epitope (CD8) (a), HIV Gag (CD8) (b), and HIV Gag (CD4) (c). The value in the center of each pie chart represents the total response to the respective stimuli. Left shows vaccine-induced responses, Center shows responses during the acute phase, and Right shows chronic phase responses.

Fig. 5.

HLA B27-restricted KK10 responses in HIV-infected controls. The pie charts depict the CD8⁺ T cell response to KK10 (a) in 2714A and 3963I and HIV Gag (b) in 2714A. The value in the center of each pie chart represents the total response to the respective stimuli. (c) Infection-induced KK10-specific CD8⁺ T cells have a predominant effector/effector memory phenotype. Red contour overlays depict the B27 KK10 tetramer⁺ CD8⁺ T cells, whereas the blue density plot depicts total CD8⁺ T cells.

Fig. 1.

Initial characterization of the vaccine-induced CD8⁺ T cell response. (a) IFN-γ ELISpot was performed to map the vaccine-induced response in HIV Gag. Either Gag Pool or individual peptides overlapping by a single amino acid spanning the region of HIV Gag p24_261–280 were used on PBMC obtained at visit 8. (b) The KK10-specific CD8⁺ T cells could be detected at visits 8 (data not shown) and 13, but not before the first immunization (visit 2), by using direct staining with B27/KK10 tetramer. The number shown on the plot represents the percentage of B27/KK10⁺ CD8⁺ T cells. (c) Memory phenotype of the KK10-specific CD8⁺ T cells, shown in red, are overlaid onto the total CD8⁺ T cell memory phenotype (gray/blue density plot). (d) The KK10-specific CD8⁺ T cells produce IFN-γ after peptide stimulation. The values on the plots represent the percentage frequency of IFN-γ-producing CD8⁺ T cells.

Fig. 3.

Comparison of 202-T07 KK10-specific CD8⁺ T cell responses pre- and postinfection. (a) Expansion of KK10-specific CD8⁺ T cells after HIV infection. CD8 expression is shown on the y axis; B27/KK10 tetramer binding on the x axis. Values shown on the density plots depict the percentage of KK10-specific CD8⁺ T cells. (b) Vaccine-induced KK10-specific clonotypes are recalled after infection. The table depicts the TCRB variable family, CDR3 sequence, TCRB joining (TCRBJ) family, and percentage frequency of each clonotype obtained from 202-T07 [before infection (202-T07 vCP205), during the acute period (202-T07 acute), and through the chronic infection period (202-T07 chronic)] and the two chronically HIV-infected control subjects, 2714A and 3963I. Matching CDR3 clonotype sequences between different time periods are highlighted in identical colors. (c) Vaccine-induced KK10-specific CD8⁺ T cells shift to a predominant effector/effector memory phenotype after infection. Red dots/contour overlays depict the B27 KK10 tetramer⁺ CD8⁺ T cells. The blue/gray density plot depicts total CD8⁺ T cells.