A phase I double blind, placebo-controlled, randomized study of a multigenic HIV-1 adenovirus subtype 35 vector vaccine in healthy uninfected adults

Abstract

Background: We conducted a phase I, randomized, double-blind, placebo-controlled trial to assess the safety and immunogenicity of escalating doses of two recombinant replication defective adenovirus serotype 35 (Ad35) vectors containing gag, reverse transcriptase, integrase and nef (Ad35-GRIN) and env (Ad35-ENV), both derived from HIV-1 subtype A isolates. The trial enrolled 56 healthy HIV-uninfected adults.

Methods: Ad35-GRIN/ENV (Ad35-GRIN and Ad35-ENV mixed in the same vial in equal proportions) or Ad35-GRIN was administered intramuscularly at 0 and 6 months. Participants were randomized to receive either vaccine or placebo (10/4 per group, respectively) within one of four dosage groups: Ad35-GRIN/ENV 2×10(9) (A), 2×10(10) (B), 2×10(11) (C), or Ad35-GRIN 1×10(10) (D) viral particles.

Results: No vaccine-related serious adverse event was reported. Reactogenicity events reported were dose-dependent, mostly mild or moderate, some severe in Group C volunteers, all transient and resolving spontaneously. IFN-γ ELISPOT responses to any vaccine antigen were detected in 50, 56, 70 and 90% after the first vaccination, and in 75, 100, 88 and 86% of Groups A-D vaccine recipients after the second vaccination, respectively. The median spot forming cells (SFC) per 10(6) PBMC to any antigen was 78-139 across Groups A-C and 158-174 in Group D, after each of the vaccinations with a maximum of 2991 SFC. Four to five HIV proteins were commonly recognized across all the groups and over multiple timepoints. CD4+ and CD8+ T-cell responses were polyfunctional. Env antibodies were detected in all Group A-C vaccinees and Gag antibodies in most vaccinees after the second immunization. Ad35 neutralizing titers remained low after the second vaccination.

Conclusion/significance: Ad35-GRIN/ENV reactogenicity was dose-related. HIV-specific cellular and humoral responses were seen in the majority of volunteers immunized with Ad35-GRIN/ENV or Ad35-GRIN and increased after the second vaccination. T-cell responses were broad and polyfunctional.

Trial registration: ClinicalTrials.gov NCT00851383.

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. Time Course of Local and Systemic Reactions Post First (Vac1) and Post Second (Vac2) Vaccination per Maximum Severity Assessment for Placebo, Group A (2×10⁹ vp), Group B (2×10¹⁰ vp), Group C (2×10¹¹ vp) and Group D (1×10¹⁰ vp).

The Y-axis of Figure 2 represents the number of volunteers experiencing reactogenicity events (panel A for local reactions and panel B for systemic reactions post first and second vaccinations, upper and lower rows respectively) for each group, while the X-axis represents the days of occurrence of the events, Day 0 being the day of vaccination. Volunteers did a self-assessment of reactogenicity with a memory card on Day 0 (evening of vaccination) and daily through Day 13, reviewed by the investigator at Days 3, 7 and 14. The figure shows the maximum severity assessment grade recorded as per the volunteer’s and clinic’s assessments combined. The severity grade of the reactogenicity events is indicated by color codes (mild: yellow; moderate: orange; severe: red).

Figure 3. IFN-γ ELISPOT Response Magnitude (SFC/10⁶ PBMC) and Responder Rate (%) to Any HIV Antigen by Time Post Vaccination (X-axis) and Dose Groups.

Gray dots: response below the cut-off to any of the 6 peptide pools; red dots: response above the cut-off to any of the 6 peptide pools. For the vaccine groups, the overlaid box plot summarizes the positive responses (i.e., the median, 1^st and 3^rd quartiles and minimum/maximum). For the baseline (BL) and placebo (Pbo) group, the box plot summarizes the negative responses and the red dot displays the single positive response at baseline.

Figure 4. IFN-γ ELISPOT Response Magnitude by peptide pool.

The panels show individual background-subtracted IFN-γ ELISPOT counts to each antigen at 2 weeks post the second vaccination for each peptide pool and by each vaccine group. The horizontal lines indicate median values for each group. SFC  =  spot forming cells.

Figure 5. Magnitude of HIV-specific antibodies.

The geometric mean of a) anti-ENV Subtype A (UG037)- and b) anti-p24 (IIIB)-specific antibody titers is shown at baseline, at 4 and 24 weeks post-first vaccination, and at 2, 14, 28, 40 and 48 weeks post-second vaccination.