Enhanced breadth of CD4 T-cell immunity by DNA prime and adenovirus boost immunization to human immunodeficiency virus Env and Gag immunogens

Abstract

A variety of gene-based vaccination approaches have been used to enhance the immune response to viral pathogens. Among them, the ability to perform heterologous immunization by priming with DNA and boosting with replication-defective adenoviral (ADV) vectors encoding foreign antigens has proven particularly effective in eliciting enhanced cellular and humoral immunity compared to either agent alone. Because adenoviral vector immunization alone can elicit substantial cellular and humoral immune responses in a shorter period of time, we asked whether the immune response induced by the prime-boost immunization was different from adenoviral vaccines with respect to the potency and breadth of T-cell recognition. While DNA/ADV immunization stimulated the CD8 response, it was directed to the same epitopes in Gag and Env immunogens of human immunodeficiency virus as DNA or ADV alone. In contrast, the CD4 response to these immunogens diversified after DNA/ADV immunization compared to each vector alone. These findings suggest that the diversity of the CD4 immune response is increased by DNA/ADV prime-boost vaccination and that these components work synergistically to enhance T-cell epitope recognition.

Figures

FIG. 1.

Definition of CD4 and CD8 epitope responses to HIV Env in BALB/c mice. BALB/c mice were injected with DNA, ADV, or DNA/ADV vectors encoding Env, as indicated in Materials and Methods, and ICS to peptide pairs in the indicated positions was determined. The peptides to the HIV Env region were synthesized as 15-mers overlapping by 11, as previously described (7, 17). Responses to the (A) CD4 or (B) CD8 epitopes are shown. The minimal threshold response is indicated by the dashed line. Red bars indicate responses above the background, while blue bars indicate epitope responses below the background that are stimulated above the threshold using a second vaccination vector; however, the values indicated by the blue bars do not show significant stimulation. Black bars show the level of response to epitopes below the background level of detection. Any value below the threshold level indicated by the horizontal dashed line, whether blue or black, is below the background level and not statistically significant. LS indicates the leader sequence, and TM refers to the transmembrane domain.

FIG. 2.

Analysis of CD4 and CD8 epitope responses of C57BL/6 mice to HIV Env. C57BL/6 mice were injected with DNA, ADV, or DNA/ADV vaccines for Env, as indicated in Materials and Methods, and ICS to peptide pairs in the indicated positions was determined. The peptides to the HIV Env region were synthesized as 15-mers overlapping by 11. Responses to the (A) CD4 or (B) CD8 epitopes are shown. The minimal threshold response is indicated by the dashed line. Red, blue, and black bars are as defined in the legend to Fig. 1. LS indicates the leader sequence, and TM refers to the transmembrane domain.

FIG. 3.

Characterization of CD4 and CD8 epitope responses of BALB/c mice to HIV Gag. BALB/c mice were injected with the indicated vectors encoding Gag as described in Materials and Methods, and ICS to the indicated pairs of peptides was determined. The peptides to the HIV Gag region were synthesized as 15-mers overlapping by 11 (16, 17). Responses to the (A) CD4 or (B) CD8 epitopes are shown. The minimal threshold response is indicated by the dashed line. Red, blue, and black bars are as defined in the legend to Fig. 1.

FIG. 4.

Specificities of the CD4 and CD8 epitope responses of C57BL/6 mice to HIV Gag. C57BL/6 mice were immunized with the specified Gag immunogen vectors as described in Materials and Methods, and ICS to peptide pools from the HIV Gag region was determined. The peptides to the HIV Gag region were synthesized as 15-mers overlapping by 11 (16, 17). Responses to the (A) CD4 or (B) CD8 epitopes are shown. The minimal threshold response is indicated by the dashed line. Red, blue, and black bars are as defined in the legend to Fig. 1.