Safety and immunogenicity study of Multiclade HIV-1 adenoviral vector vaccine alone or as boost following a multiclade HIV-1 DNA vaccine in Africa

Abstract

Background: We conducted a double-blind, randomized, placebo-controlled Phase I study of a recombinant replication-defective adenovirus type 5 (rAd5) vector expressing HIV-1 Gag and Pol from subtype B and Env from subtypes A, B and C, given alone or as boost following a DNA plasmid vaccine expressing the same HIV-1 proteins plus Nef, in 114 healthy HIV-uninfected African adults.

Methodology/principal findings: Volunteers were randomized to 4 groups receiving the rAd5 vaccine intramuscularly at dosage levels of 1×10(10) or 1×10(11) particle units (PU) either alone or as boost following 3 injections of the DNA vaccine given at 4 mg/dose intramuscularly by needle-free injection using Biojector® 2000. Safety and immunogenicity were evaluated for 12 months. Both vaccines were well-tolerated. Overall, 62% and 86% of vaccine recipients in the rAd5 alone and DNA prime - rAd5 boost groups, respectively, responded to the HIV-1 proteins by an interferon-gamma (IFN-γ) ELISPOT. The frequency of immune responses was independent of rAd5 dosage levels. The highest frequency of responses after rAd5 alone was detected at 6 weeks; after DNA prime - rAd5 boost, at 6 months (end of study). At baseline, neutralizing antibodies against Ad5 were present in 81% of volunteers; the distribution was similar across the 4 groups. Pre-existing immunity to Ad5 did not appear to have a significant impact on reactogenicity or immune response rates to HIV antigens by IFN-γ ELISPOT. Binding antibodies against Env were detected in up to 100% recipients of DNA prime - rAd5 boost. One volunteer acquired HIV infection after the study ended, two years after receipt of rAd5 alone.

Conclusions/significance: The HIV-1 rAd5 vaccine, either alone or as a boost following HIV-1 DNA vaccine, was well-tolerated and immunogenic in African adults. DNA priming increased the frequency and magnitude of cellular and humoral immune responses, but there was no effect of rAd5 dosage on immunogenicity endpoints.

Trial registration: ClinicalTrials.gov NCT00124007.

Figure 1. CONSORT Flow Diagram.

Number of individuals assessed for eligibility, enrolled and randomized to study vaccine(s) and respective placebo, followed-up and analyzed.

Figure 2. Solicited Local and Systemic Events.

Figure 2a; Local reactogenicity and systemic signs and symptoms collected over 3 days post vaccination. Maximum severity of local reactions was significantly greater after rAd5 than after placebo (p = 0.006 and p<0.001 for rAd5 alone and rAd5 boost, respectively). For systemic signs and symptoms, the severity was significantly greater after DNA (p = 0.036) and after rAd5 boost (p = 0.028), than after the corresponding placebo. Figure 2b; Local reactogenicity and systemic events post rAd5 by dosage. Combining low dosage (LD) groups and high dosage (HD) groups, the maximum systemic reaction per volunteer post rAd5 was significantly higher (p = 0.025) in the HD group than in the LD group (41% versus 21%, respectively, were moderate or severe). Mild: open bars; Moderate: cross-hatched bars; and Severe: dark bars.

Figure 3. Impact of DNA prime on ELISPOT responses.

Comparison of percent ELISPOT responders after rAd5 alone (Groups A and B) versus DNA prime - rAd5 boost over time (Groups C and D). Vertical lines represent 95% Confidence Intervals.

Figure 4. Impact of DNA prime on ELISPOT magnitude.

Values plotted are the mean background-subtracted ELISPOT counts (Spot Forming Cells, SFC) over all positive peptide responses per volunteer at that visit. Shaded bars are subjects with any positive response at 4 weeks post 3^rd DNA, white boxes are those with no positive responses at this time point.

Figure 5. Magnitude of ELISPOT and % response rate.

The magnitude of the response was measured by SFC per million peripheral blood mononuclear cells (SFC/m PBMC). The x-axis row one shows the peptide pool, row two the % response rate and row three the vaccine group. Black dots indicate positive responses, defined by background-subtracted values greater than the cutoff, more than 3 times mean background SFC count, and a coefficient of variation of not more than 70% amongst replicate wells. The rAd5 response rates correspond to both dose groups combined. The box plots summarize positive responses only (i.e., median, 1^st and 3^rd quartiles, minimum/maximum). The cut-offs for EnvA, EnvB, Gag, Nef, PolB1 and PolB2, as determined by the level of non-specific responses from at least 180 samples from unvaccinated individuals, are 40, 51, 54, 68, 51 and 38 respectively. The Pol response is the maximum of PolB1 and PolB2 and positive if either one is positive.

Figure 6. Induction of CD8 T cell-mediated inhibition of HIV-1-IIIB replication following vaccination with a DNA prime - rAd5 boost or rAd5 alone regimen.

Viral inhibition was assessed in placebo recipients and prior to any vaccination (•); following DNA alone (▪); DNA prime - rAd5 boost at 6 and 12 weeks (▴and ▵respectively) and after rAd5 alone at 6 and between 36 to 48 weeks (♦ and ⋄ respectively). The 1.13 log₁₀ inhibition value above which inhibition is considered HIV-1 specific is indicated by the hashed line. Medians for all groups are indicated (—).

Figure 7. HIV antibody titers.

Distribution of HIV-specific antibody titers at 1 month post rAd5 alone (Groups A and B) and rAd5 boost (Groups C and D) in vaccine recipients, by protein and treatment group. The Y-axis shows the antibody titer on a log scale with box plots showing the median, 1^st and 3^rd quartiles.