A phase 1b randomized study of the safety and immunological responses to vaccination with H4:IC31, H56:IC31, and BCG revaccination in Mycobacterium tuberculosis-uninfected adolescents in Cape Town, South Africa

Abstract

Background: Tuberculosis (TB) remains the leading cause of infectious disease-related death. Recently, a trial of BCG revaccination and vaccination with H4:IC31, a recombinant protein vaccine, in South African adolescents (Aeras C-040-404) showed efficacy in preventing sustained QuantiFERON (QFT) conversion, a proxy for Mycobacterium tuberculosis (M.tb) infection. A phase 1b trial of 84 South African adolescents was conducted, concurrent with Aeras C-040-404, to assess the safety and immunogenicity of H4:IC31, H56:IC31 and BCG revaccination, and to identify and optimize immune assays for identification of candidate correlates of protection in efficacy trials.

Methods: Two doses of H4:IC31 and H56:IC31 vaccines were administered intramuscularly (IM) 56 days apart, and a single dose of BCG (2-8 × 10⁵ CFU) was administered intradermally (ID). T-cell and antibody responses were measured using intracellular cytokine staining and binding antibody assays, respectively. Binding antibodies and CD4+/CD8+ T-cell responses to H4- and H56-matched antigens were measured in samples from all participants. The study was designed to characterize safety and immunogenicity and was not powered for group comparisons. (Clinicaltrials.gov NCT02378207).

Findings: In total, 481 adolescents (mean age 13·9 years) were screened; 84 were enrolled (54% female). The vaccines were generally safe and well-tolerated, with no reported severe adverse events related to the study vaccines. H4:IC31 and H56:IC31 elicited CD4+ T cells recognizing vaccine-matched antigens and H4- and H56-specific IgG binding antibodies. The highest vaccine-induced CD4+ T-cell response rates were for those recognizing Ag85B in the H4:IC31 and H56:IC31 vaccinated groups. BCG revaccination elicited robust, polyfunctional BCG-specific CD4+ T cells, with no increase in H4- or H56-specific IgG binding antibodies. There were few antigen-specific CD8+ T-cell responses detected in any group.

Interpretation: BCG revaccination administered as a single dose ID and both H4:IC31 and H56:IC31 administered as 2 doses IM had acceptable safety profiles in healthy, QFT-negative, previously BCG-vaccinated adolescents. Characterization of the assays and the immunogenicity of these vaccines may help to identify valuable markers of protection for upcoming immune correlates analyses of C-040-404 and future TB vaccine efficacy trials.

Funding: NIAID and Aeras.

Keywords: BCG; H4:IC31; H56:IC31; Mycobacterium tuberculosis.

Fig. 1

HVTN 602/AERAS A-042 CONSORT flow diagram.

Fig. 2

Background-subtracted readouts from the QFT-GIT. Assay magnitudes (IFN-γ ELISA readout) are plotted on a log-scale, by treatment group and visit. Each participant is represented as a single line with one symbol per visit/sample. A dashed line indicates the manufacturer's recommended positivity threshold (≥0.35 IU/mL). The shaded gray area indicates the “uncertainty” area as defined in (12) in which they showed changes in response magnitude from below the shaded region (<0.2 IU/mL) to a level above the region (>0·7 IU/mL) were more strongly associated with increased risk of TB disease. The post-vaccine responses among participants in the H56:IC31 group may indicate vaccine-induced responses as H56 contains one of the antigens in the QFT-GIT assay.

Fig. 3

Antigen-specific CD4+ T-cell responses after re-stimulation with vaccine-matched peptide pools or BCG. Frequency of CD4+ T cells expressing at least 2 of the cytokines IL-2, TNF-α and IFN-γ in response to (a) Ag85B, (b) TB10.4, (c) ESAT-6 and (d) BCG, at study days 0, 14/28, 70 and 168 after vaccination (day 28 for BCG group and day 14 for all other groups). Respective response rates are indicated above each box plot. Comparisons to baseline response rates were made using McNemar's test (top of each panel) and to baseline magnitudes with the Wilcoxon Signed rank test (bottom of each panel) (* indicates FWER-p < 0·05). The mid-line of the box denotes the median and the ends of the box denote the 25th and 75th percentiles. Whiskers extend to the most extreme data points, no more than 1·5 times the interquartile range.

Fig. 4

Antigen-specific CD8+ T-cell responses after re-stimulation with BCG. Frequency of CD8+ T cells expressing at least 2 of the cytokines IL-2, TNF-α and IFN-γ in response BCG at study days 0, 14/28, 70 and 168 after vaccination (day 28 for BCG group and day 14 for all other groups). Respective response rates are indicated above each box plot. Comparisons to baseline response rates were made using McNemar's test and to baseline magnitudes with the Wilcoxon Signed rank test; no responses met the significance criteria FWER-p < 0·05. The mid-line of the box denotes the median and the ends of the box denote the 25th and 75th percentiles. Whiskers extend to the most extreme data points, no more than 1·5 times the interquartile range.

Fig. 5

Cytokine expression of stimulated CD4+ T cells. Boxplots show the median and interquartile (IQR) of the percentage of CD4+ T cells expressing the combination of cytokines indicated on the x-axis. The magnitude is background-subtracted. Panels show Ag85B-specific responses among (a) H4:IC31 and (b) H56:IC31 recipients and (c) BCG-specific responses among BCG recipients. Comparisons to baseline were made within each functional subset using a Wilcoxon signed-rank test (*FWER-p < 0·05).

Fig. 6

H4- and H56-specific IgG binding antibody. Levels of binding antibody were measured using a binding antibody multiplex assay. Boxplots show the median and IQR of the net response on a log scale. Panels show response rates (upper graphs) and net response magnitude (lower graphs) to the H4 recombinant fusion protein (a) and the H56 recombinant fusion protein (b).