DNA Priming Increases Frequency of T-Cell Responses to a Vesicular Stomatitis Virus HIV Vaccine with Specific Enhancement of CD8+ T-Cell Responses by Interleukin-12 Plasmid DNA

Abstract

The HIV Vaccine Trials Network (HVTN) 087 vaccine trial assessed the effect of increasing doses of pIL-12 (interleukin-12 delivered as plasmid DNA) adjuvant on the immunogenicity of an HIV-1 multiantigen (MAG) DNA vaccine delivered by electroporation and boosted with a vaccine comprising an attenuated vesicular stomatitis virus expressing HIV-1 Gag (VSV-Gag). We randomized 100 healthy adults to receive placebo or 3 mg HIV-MAG DNA vaccine (ProfectusVax HIV-1 gag/pol or ProfectusVax nef/tat/vif, env) coadministered with pIL-12 at 0, 250, 1,000, or 1,500 μg intramuscularly by electroporation at 0, 1, and 3 months followed by intramuscular inoculation with 3.4 × 10⁷ PFU VSV-Gag vaccine at 6 months. Immune responses were assessed after the prime and boost and 6 months after the last vaccination. High-dose pIL-12 increased the magnitude of CD8⁺ T-cell responses postboost compared to no pIL-12 (P = 0.02), while CD4⁺ T-cell responses after the prime were higher in the absence of pIL-12 than with low- and medium-dose pIL-12 (P ≤ 0.05). The VSV boost increased Gag-specific CD4⁺ and CD8⁺ T-cell responses in all groups (P < 0.001 for CD4⁺ T cells), inducing a median of four Gag epitopes in responders. Six to 9 months after the boost, responses decreased in magnitude, but CD8⁺ T-cell response rates were maintained. The addition of a DNA prime dramatically improved responses to the VSV vaccine tested previously in the HVTN 090 trial, leading to broad epitope targeting and maintained CD8⁺ T-cell response rates at early memory. The addition of high-dose pIL-12 given with a DNA prime by electroporation and boosted with VSV-Gag increased the CD8⁺ T-cell responses but decreased the CD4⁺ responses. This approach may be advantageous in reshaping the T-cell responses to a variety of chronic infections or tumors. (This study has been registered at ClinicalTrials.gov under registration no. NCT01578889.).

Keywords: DNA prime; HIV; IL-12; T cell; VSV vector; vaccine.

FIG 1

Trial schema and CONSORT statement 2010 flow diagram. Participants were randomized into one of four groups, each with a vaccine/placebo ratio of 22/3. The vaccine and adjuvant doses were mixed and divided between two injection sites on opposite deltoids. The numbers of participants enrolled, randomized, followed up, and analyzed are shown for placebo and treatment groups. pIL-12, plasmid IL-12 DNA.

FIG 2

Gag-specific T-cell responses. CD4⁺ (A and C) and CD8⁺ (B and D) T-cell responses to Gag were measured 2 weeks after the 3rd DNA prime, (prime), 2 weeks after the VSV boost (boost), and 6 months after the boost (memory) by ICS. Shown are response rates (percentage) (A and B) and response magnitudes (C and D) of CD4⁺ or CD8⁺ T cells producing IFN-γ and/or IL-2 for placebo recipients (combined for groups 1 to 4) and vaccinees in each treatment group. Positive responses are shown in filled red circles, and negative responses are shown in open blue triangles (C and D). Box plots represent the distribution for the positive responders only. Response rates were compared using Fisher's exact test (A and B); response magnitudes were compared using Wilcoxon's rank sum test for the comparisons between treatment groups among the responders and using Wilcoxon's signed-rank test for the comparisons between visits among the participants with a positive response at either or both visits (C and D). *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001. Significance bars represent longitudinal comparisons.

FIG 3

HIV-specific T-cell responses to any protein. CD4⁺ (A and C) and CD8⁺ (B and D) T-cell responses to Env, Pol, Gag, Nef, and Vif were measured 2 weeks after the 3rd DNA prime (prime), 2 weeks after the VSV boost (boost), and 6 months after the boost (memory) by ICS. Shown are response rates (percentage) (A and B) and response magnitudes (C and D) for the sum of individual antigen responses of CD4⁺ or CD8⁺ T cells producing IFN-γ and/or IL-2 for placebo recipients (combined for groups 1 to 4), and vaccinees in each treatment group. Positive responses are shown in filled red circles, and negative responses are shown in open blue triangles (C and D). Box plots represent the distribution for the positive responders only. Response rates were compared using Fisher's exact test (A and B); response magnitudes were compared using Wilcoxon's rank sum test for the comparisons between treatment groups among the responders, and using Wilcoxon's signed-rank test for the comparisons between visits among the participants with a positive response at either or both visits (C and D). *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001. Significance bars without tails represent the comparisons between visits within the same group, and those with tails represent the comparisons between treatment groups.

FIG 4

Functionality analysis using COMPASS. Expression of different combinations of functional markers is represented as heat maps of COMPASS posterior probabilities for Gag-specific CD4⁺ (A) and CD8⁺ T cells (B), and Env-specific CD4⁺ (C) and CD8⁺ T cells (D) at months 3.5, 6.5, and 12. Columns correspond to the different cell subsets modeled by COMPASS, color coded by the cytokines they express (where white represents “off,” shaded represents “on,” and the color grouping represents the degree of functionality), and ordered by degree of functionality from one function on the left to five functions on the right. Subsets with maximum posterior probabilities of <0.005 were removed from the heat map. Rows correspond to the average within each treatment group at each time point; all time points are averaged for controls. Each cell shows the probability that the corresponding cell subset (column) exhibits an Ag-specific response in the corresponding treatment group (row), where the probability is color coded from white (zero) to purple (one). Subject-level posterior probabilities reflect the certainty from the COMPASS model that the subset exhibits an antigen-specific response in a subject (i.e., that the magnitude of the stimulated sample is above the magnitude of the [paired] nonstimulated sample). These subject-specific and category-specific posterior probabilities are summarized by their average across subjects within different treatment groups and time points, giving rise to the heat maps shown here. Below the heat maps, functionality scores provide a summary measure, defined as the proportion of antigen-specific subsets detected among all possible ones, and are not shown for controls. VSV-Gag boost led to significantly increased functionality scores for Gag-specific CD4⁺ T cells (P < 0.0001 for all groups) and for Gag-specific CD8⁺ T cells in groups 1 (P = 0.047), 3 (P = 0.032), and 4 (P = 0.032). *, does not apply to group 2. Group 1, green squares, no IL-12; group 2, lavender circles, 250 μg IL-12; group 3, plum triangles, 1,000 μg IL-12; group 4, purple diamonds, 1,500 μg IL-12.

FIG 5

Number of targeted epitopes in Gag. The number of epitopes in Gag was determined 2 weeks after the last DNA prime (V10, month 3.5) and 2 weeks after the VSV boost (V15, month 6.5) by IFN-γ ELISpot using a matrix approach. Responses to two overlapping 15-mer peptides were counted as one epitope. Each data point represents the number of targeted epitopes per vaccinee; lines connect longitudinal data for the same individual. Epitope mapping was restricted to vaccinees who had a detectable CD4⁺ and/or CD8⁺ T-cell response at V15 as measured by ICS and for whom samples were available.