A double-blind, randomised, placebo-controlled, dose-finding trial of the novel tuberculosis vaccine AERAS-402, an adenovirus-vectored fusion protein, in healthy, BCG-vaccinated infants

Abstract

Background: Several novel tuberculosis vaccines are currently in clinical trials, including AERAS-402, an adenovector encoding a fusion protein of Mycobacterium tuberculosis antigens 85A, 85B, and TB10.4. A multicentred trial of AERAS-402 safety and immunogenicity in healthy infants was conducted in three countries in sub-Saharan Africa, using an adaptive design.

Methods: In a double-blind, randomised, placebo-controlled, dose-finding trial, we enrolled BCG-vaccinated, HIV-uninfected infants aged 16-26 weeks. Infants in the safety/dose-finding phase received two doses of AERAS-402 across three dose levels, or placebo, intramuscularly on days 0 and 28. Infants in the expanded safety phase received three doses of the highest dose level, with the 3rd dose at day 280. Follow up for safety and immunogenicity was for up to two years.

Results: We enrolled 206 infants (52 placebo and 154 AERAS-402 recipients) into the dose-finding phase and 281 (141 placebo and 140 AERAS-402 recipients) into the expanded safety phase. Safety data were acceptable across all dose levels. No vaccine-related deaths were recorded. A single serious adverse event of tachypnoea was deemed related to study vaccine. Antibodies directed largely against Ag85A and Ag85B were detected. Low magnitude CD4+ and CD8+ polyfunctional T cell responses were observed at all dose levels. The addition of a third dose of AERAS-402 at the highest dose level did not increase frequency or magnitude of antibody or CD8+ T cell responses.

Conclusions: AERAS-402 has an acceptable safety profile in infants and was well tolerated at all dose levels. Response rate was lower than previously seen in BCG vaccinated adults, and frequency and magnitude of antigen-specific T cells were not increased by a third dose of vaccine.

Keywords: Adenovirus vectored; Infant; Novel TB vaccine trial; Tuberculosis vaccine.

Conflict of interest statement

Conflict of Interest Statement:

None declared

Copyright © 2015 Elsevier Ltd. All rights reserved.

Figures

Figure 1

Consort diagram

Figure 2.. PBMC ICS responses for dose selection.

Participants were vaccinated with placebo (black symbols) or AERAS-402 at doses of 1.5 × 10^10 (red symbols), 3 × 10^10 (blue symbols), or 1 × 10^11 (green symbols) vp on study day 0 and 28. Blood was collected 28 days following the second vaccination (study day 56). PBMC were isolate for the measurement of CD4+ (A) and CD8+ (B) DMSO-subtracted T-cell responses against Ag85A, Ag85B, and TB10.4 peptide pools using intracellular cytokine staining. Total responses (percentage of cells making any of the three IFN-γ, IL-2, or TNF alone or in combination) are shown as a percentage of the parent population. Fisher’s Exact Test was used to determine responder status. Closed circles (•) represent responders and (X) represents non-responders. Bars represent median responses by group. Statistical significance was determined initially by Kruskal-Wallis analysis, and vaccine groups were then compared to placebo using Mann-Whitney U Tests, which were adjusted for multiplicity by T cell and antigen using the Holm method. P-values are indicated by asterisks: <0.05 (*), <0.01 (**), <0.001 (***), ≤0.0001 (****).

Figure 3.. PBMC T cell ICS responses to high dose AERAS-402.

Participants were vaccinated with placebo (black symbols) or 1 × 10^11 vp AERAS-402 (red symbols) on study day 0, 28, and 280. Blood was collected on study days 56, 280, 308, and at the end of the study (study days 448–664). PBMC were isolate for the measurement of CD4+ (A–C) and CD8+ (D–F) DMSO-subtracted T-cell responses against Ag85A (A, D), Ag85B (B, E), and TB10.4 (C, F) peptide pools using intracellular cytokine staining. Total responses (percentage of cells making any of the three IFN-γ, IL-2, or TNF alone or in combination) are shown as a percentage of the parent population. Fisher’s Exact Test was used to determine responder status. Closed circles (•) represent responders and (X) represents non-responders. Bars represent group median responses. The high-dose AERAS-402 group was compared to placebo at each timepoint using Mann-Whitney U Tests, which were adjusted for multiplicity by T cell and antigen using the Holm method. P-values are indicated by asterisks: <0.05 (*), <0.01 (**), <0.001 (***), ≤0.0001 (****).

Figure 4.. PBMC T cell ELISpot responses to high dose AERAS-402.

Participants were vaccinated with placebo (black symbols) or 1 × 10^11 vp AERAS-402 (red symbols) on study day 0, 28, and 280. Blood was collected on study days 56, 280, 308, and at the end of the study (study days 448–664). PBMC were isolate for the measurement of responses against Ag85A (A), Ag85B (B), and TB10.4 (C) peptide pools. Total spot-forming units (SFU) were background- (DMSO stimulation) subtracted and plotted. Fisher’s Exact Test was used to determine responder status. Closed circles (•) represent responders and (X) represents non-responders. Bars represent group median responses. High-dose AERAS-402 and placebo were compared at each timepoint using Mann-Whitney U Tests and adjusted for multiplicity by antigen using the Holm method. P-values are indicated by asterisks: <0.05 (*), <0.01 (**), <0.001 (***), ≤0.0001 (****).

Figure 5.. Polyfunctional analysis of PBMC T cell responses on days 308 and at the end of the study.

Participants were vaccinated with placebo (black symbols) or 1 × 10^11 vp AERAS-402 (red symbols) on study day 0, 28, and 280. Blood was collected on study day 308 (A, C) and at the end of the study (study days 448–664; B, D). PBMC were isolate for the measurement of CD4+ (A,B) and CD8+ (C,D) responses against the Ag85B peptide pool by intracellular cytokine staining. Boolean gating was performed to obtain the percentage of cells making IFN- γ, IL-2, or TNF alone or in combination. Symbols represent individual responses for each possible cytokine combination. Bars represent group median responses.

Figure 6.. Antibody responses following vaccination with high dose AERAS-402.

Participants were vaccinated with placebo (black symbols) or 1 × 10^11 vp AERAS-402 (red symbols) on study day 0, 28, and 280. Blood was collected on study days 56, 280, 308, and at the end of the study (study days 448–664). Plasma was isolate for the measurement of antibody responses against Ag85A (A), Ag85B (B), and TB10.4 (C) by antigen-specific ELISA. The OD values, which correspond to the concentration of the antigen-specific antibodies in the plasma, are plotted. Symbols represent individual responses. Bars represent group median responses. Statistical significance of change in antibody response over time was determined initially by Friedman analysis. Then changes from baseline by timepoint were analyzed using Wilcoxon signed-rank tests and adjusted for multiplicity by antigen using the Holm method. High-dose AERAS-402 was then compared to placebo at each timepoint using Mann-Whitney U Tests, which were adjusted for multiplicity by antigen using the Holm method. P-values are indicated by asterisks: <0.05 (*), <0.01 (**), <0.001 (***), ≤0.0001 (****).