The novel tuberculosis vaccine, AERAS-402, induces robust and polyfunctional CD4+ and CD8+ T cells in adults

Abstract

Rationale: AERAS-402 is a novel tuberculosis vaccine designed to boost immunity primed by bacillus Calmette-Guérin (BCG), the only licensed vaccine.

Objectives: We investigated the safety and immunogenicity of AERAS-402 in healthy Mycobacterium tuberculosis-uninfected BCG-vaccinated adults from a tuberculosis-endemic region of South Africa.

Methods: Escalating doses of AERAS-402 vaccine were administered intramuscularly to each of three groups of healthy South African BCG-vaccinated adults, and a fourth group received two injections of the maximal dose. Participants were monitored for 6 months, with all adverse effects documented. Vaccine-induced CD4(+) and CD8(+) T-cell immunity was characterized by an intracellular cytokine staining assay of whole blood and peripheral blood mononuclear cells.

Measurements and main results: AERAS-402 was well tolerated, and no vaccine-related serious adverse events were recorded. The vaccine induced a robust CD4(+) T-cell response dominated by cells coexpressing IFN-gamma, tumor necrosis factor-alpha, and IL-2 ("polyfunctional" cells). AERAS-402 also induced a potent CD8(+) T-cell response, characterized by cells expressing IFN-gamma and/or tumor necrosis factor-alpha, which persisted for the duration of the study.

Conclusions: Vaccination with AERAS-402 is safe and immunogenic in healthy adults. The immunity induced by the vaccine appears promising: polyfunctional T cells are thought to be important for protection against intracellular pathogens such as Mycobacterium tuberculosis, and evidence is accumulating that CD8(+) T cells are also important. AERAS-402 induced a robust and durable CD8(+) T-cell response, which appears extremely promising. Clinical trial registered with www.sanctr.gov.za (NHREC no. 1381).

Figure 1.

Frequency of Ag85A/B-specific T cells induced by AERAS-402, as measured by flow cytometry after incubation of peripheral blood mononuclear cells with a peptide pool of the antigens. CD4⁺ T-cell (left) and CD8⁺ T-cell (right) responses, in AERAS-402–vaccinated (blue boxes) and placebo-vaccinated (red boxes) participants are shown. Participants from (A and B) group 1, (C and D) group 2, and (E and F) group 3 received a single, escalating dose of AERAS-402 on Day 0 (indicated by the black arrow under the x axis). (G and H) Group 4 participants received two doses of AERAS-402 on Days 0 and 56 (indicated by the black arrows under the x axis), and were bled additionally on Days 56, 63, and 70. Total cytokine-positive frequencies denote any T cell that expresses IFN-γ, tumor necrosis factor-α, or IL-2 alone or in combination. Background values (unstimulated) were subtracted for each condition from each individual. For each plot, the median is represented by the horizontal line, the interquartile range by the box, and the range by the whiskers. The open circles and accompanying numbers represent high responders that exceed the maximal value on the scale. The P values indicated were derived by comparing responses with those at baseline, using the Mann-Whitney U test.

Figure 2.

Frequency of (A, C, and E) Ag85A/B-specific and (B, D, and F) TB10.4-specific CD4⁺ T cells induced by AERAS-402, as measured by flow cytometry after incubation of whole blood with a peptide pool of the antigens. Vaccinations for groups 3 and 4 are indicated with blue and red arrows, respectively, under the x axis. (A–D) Total (any) cytokine-expressing and (E and F) polyfunctional IFN-γ⁺IL-2⁺TNF-α⁺ CD4⁺ T-cell responses are shown for group 3 (single high dose, administered on Day 0, blue arrow) and group 4 (two doses of the vaccine, administered on Days 0 and 56, red arrows). Each line displayed represents a vaccine participant. Background values (unstimulated) were subtracted for each condition from each individual. The P values indicated were derived by comparing responses with those at baseline, using the Mann-Whitney U test.

Figure 3.

Frequency of (A and C) Ag85A/B-specific and (B and D) TB10.4-specific CD8⁺ T cells induced by AERAS-402, as measured by flow cytometry after incubation of whole blood with a peptide pool of the antigens. Vaccinations for groups 3 and 4 are indicated with blue and red arrows, respectively, under the x axis. Total (any) cytokine-expressing CD8⁺ T-cell responses are shown, for group 3 (single high dose, administered on Day 0, blue arrow) and group 4 (2 doses of the vaccine, administered on Days 0 and 56, red arrows). Each line displayed represents a vaccine participant. Background values (unstimulated) were subtracted for each condition from each individual. The P values indicated were derived from comparing responses with those at baseline, using the Mann-Whitney U test.

Figure 4.

Detailed analysis of cytokine expression patterns of specific CD4⁺ and CD8⁺ T cells induced by AERAS-402, as measured by flow cytometry after incubation of whole blood with a peptide pool of the antigens. Patterns of single or combined expression of the helper T-cell type 1 cytokines in (A) Ag85A/B-specific and (B) TB10.4-specific CD4⁺ T cells of participants vaccinated with a single high dose of AERAS-402 (group 3) are shown, as frequencies of specific CD4⁺ T cells. (C) Among these participants, pie charts represent the mean proportions of cells producing three cytokines (red), two cytokines (blue), and one cytokine only (green), of the total cytokine CD4⁺ T-cell response, on Days 7, 28, and 84 postvaccination. (D and E) Again among these participants, the frequency of specific IL-17–expressing CD4⁺ T cells, after AERAS-402 vaccination, is shown for (D) AERAS-402–vaccinated and (E) placebo-vaccinated participants. Bacillus Calmette-Guérin was used a positive control. (F and G) Patterns of single or combined expression of the cytokines in (F) Ag85A/B-specific and (G) TB10.4-specific CD8⁺ T cells of participants vaccinated with a single high dose of AERAS-402 (group 3) are shown, as frequencies of specific CD8⁺ T cells. Background values (unstimulated) were subtracted for each condition from each individual. The open circles and accompanying numbers represent high responders that exceed the maximal value on the scale. For each plot, the median is represented by the horizontal line, the interquartile range by the box, and the range by the whiskers. Differences between prevaccination and postvaccination responses were evaluated with the Mann-Whitney U test: P values less than 0.05 are shown.

Figure 5.

Ad35-neutralizing antibody titers induced by AERAS-402 vaccination of group 3 and 4 participants. (A and B) Longitudinal analysis of Ad35-neutralizing antibody titers on Days 0, 28, 84, and 182 postvaccination in serum from (A) group 3 participants (single high dose) and on Days 0, 28, 56, 84, and 182 postvaccination in serum from (B) group 4 participants (two high doses). (C and D) Comparison of Ad35-neutralizing antibody titers on Days 0, 28, and 182 postvaccination in serum from (C) group 3 and 4 participants and from (D) placebo recipients.