Live-attenuated Mycobacterium tuberculosis vaccine, MTBVAC, in adults with or without M tuberculosis sensitisation: a single-centre, phase 1b-2a, double-blind, dose-escalation, randomised controlled trial

Abstract

Background: An effective adult vaccine is needed to control tuberculosis. We evaluated the safety and immunogenicity of a live-attenuated Mycobacterium tuberculosis vaccine (MTBVAC).

Methods: This single-centre, phase 1b-2a, double-blind, dose-escalation, randomised controlled trial (NCT02933281) enrolled South African adults previously vaccinated with BCG, who were HIV negative and aged 18-50 years, with or without M tuberculosis sensitisation assessed by QuantiFERON-tuberculosis Gold-Plus assay (QFT). Participants were recruited from the local community and randomly allocated (2:1) to receive MTBVAC (5 × 10³, 5 × 10⁴, 5 × 10⁵, or 5 × 10⁶ colony-forming unit [CFU] doses) or BCG revaccination (5 × 10⁵ CFU dose). The primary outcomes were the occurrence of systemic solicited adverse events within 7 days and unsolicited adverse events within 28 days after vaccination, the occurrence of solicited and unsolicited injection-site reactions within 84 days after vaccination, and the occurrence of serious adverse events (SAEs) until the end of study, 365 days after vaccination. Data were analysed per modified intention to treat. The trial is now complete and closed.

Findings: Between Jan 15, 2019, and Sept 7, 2020, 485 participants provided consent and were screened. 144 participants were enrolled and 143 (99%) were vaccinated. BCG was administrated to 47 (33%) of 143 and MTBVAC to 96 (67%) of 143. 12 participants with QFT-negative results and 12 with QFT-positive results were randomly allocated to receive each dose of MTBVAC and 24 participants with QFT-negative results and 24 with QFT-positive results were randomly allocated to receive BCG revaccination. Injection-site pain, discharge, erythema, and swelling increased with MTBVAC dose level. MTBVAC 5 × 10⁵ CFU recipients reported a similar proportion of related adverse events (23 [96%] of 24) as BCG recipients (45 [96%] of 47). MTBVAC recipients who were QFT positive reported more injection-site reactions (46 [96%] of 48; 95% CI 85·7-99·5) than MTBVAC recipients who were QFT negative (32 [67%] of 48; 51·6-79·6). No vaccine-related SAEs were reported. All doses of MTBVAC were immunogenic; vaccine-induced antigen-specific CD4 T-cell responses peaked 28 days after vaccination. The MTBVAC 5 × 10⁵ and 5 × 10⁶ CFU doses induced T-helper-cell-1 cytokine-expressing CD4 T-cell responses that exceeded BCG-induced responses in participants who were QFT negative and QFT positive.

Interpretation: MTBVAC at the 5 × 10⁵ dose showed similar safety and reactogenicity and greater immunogenicity when compared to BCG. These results suggest that the 5 × 10⁵ dose of MTBVAC could be selected for a subsequent efficacy evaluation.

Funding: Congressionally Directed Medical Research Programmes and US National Institutes of Health.

Figure 1:. Trial profile by MTBVAC dose and QFT status

The safety analysis included all participants who received at least one dose of the study intervention. The immunology analytic set consisted of all participants without treatment deviations. CFU=colony-forming unit. MTBVAC=live-attenuated Mycobacterium tuberculosis vaccine. QFT=QuantiFERON-tuberculosis Gold-Plus assay.

Figure 2:. Risk difference in local and systemic adverse events

Differences in the proportions of participants between MTBVAC dose cohorts who reported the listed local and systemic adverse events and BCG recipients. Shifts to the right indicate a greater risk in the higher MTBVAC dose cohort than BCG. CIs that do not include zero are considered statistically significant. MTBVAC=live-attenuated M tuberculosis vaccine.

Figure 3:. Kinetics of cytokine-expressing MTBVAC-specific CD4 or CD8 T-cell responses in individuals vaccinated with different doses of MTBVAC or BCG and stratified by QFT status at screening

Frequencies of MTBVAC-specific T cells expressing any combination of IFN-γ, IL-2, TNF, IL-17A, or IL-22 (any cytokine-expressing CD4 T cells) measured after MTBVAC stimulation by whole-blood intracellular cytokine staining assay in MTBVAC or BCG vaccinees stratified by QFT status at screening. (A) Individual longitudinal trajectories of CD4 T-cell responses in participants who were QFT negative (top panels) or QFT positive (bottom panels) at screening, stratified by treatment group and dose at the indicated timepoints. Each line represents one participant. (B) Frequencies of CD4 T-cell responses in participants who were QFT negative (top panels) or QFT positive (bottom panels) at screening. Horizontal lines represent medians, boxes the IQR, and whiskers the range. p values were computed by generalised estimating equation (GEE) linear regression assessing the difference between each timepoint after vaccination relative to before vaccination (day 0). Values were adjusted for multiple testing using the Holm method. Only p values lower than 0·1 are shown. The percentage of responders (bottom of the graphs) at each timepoint was computed using COMPASS, relative to baseline to take into account the fact that populations were non-naive at baseline because of either previous BCG vaccination at birth or previous Mycobacterium tuberculosis exposure for QFT-positive groups (appendix p 14). (C, D) Median longitudinal trajectories of CD4 (C) and CD8 (D) T-cell frequencies expressing any combination of IFN-γ, IL-2, TNF, IL-17A, or IL-22 (C top panels and D) or co-expressing IFN-γ, IL-2, and TNF (C, bottom panels) in participants who were QFT negative (left) and QFT positive (right), stratified by treatment group and dose at the indicated timepoints. p values between cohorts were calculated using the Kruskal-Wallis test. Error bars denote IQRs. Frequencies of cytokine-positive CD4 T cells in the unstimulated control were subtracted from MTBVAC-stimulated frequencies. CFU=colony-forming unit. IFN=interferon. IL=interleukin. MTBVAC=live-attenuated M tuberculosis vaccine. NA=not applicable. QFT=QuantiFERON-tuberculosis Gold-Plus assay. TNF=tumour necrosis factor.

Figure 3:. Kinetics of cytokine-expressing MTBVAC-specific CD4 or CD8 T-cell responses in individuals vaccinated with different doses of MTBVAC or BCG and stratified by QFT status at screening

Frequencies of MTBVAC-specific T cells expressing any combination of IFN-γ, IL-2, TNF, IL-17A, or IL-22 (any cytokine-expressing CD4 T cells) measured after MTBVAC stimulation by whole-blood intracellular cytokine staining assay in MTBVAC or BCG vaccinees stratified by QFT status at screening. (A) Individual longitudinal trajectories of CD4 T-cell responses in participants who were QFT negative (top panels) or QFT positive (bottom panels) at screening, stratified by treatment group and dose at the indicated timepoints. Each line represents one participant. (B) Frequencies of CD4 T-cell responses in participants who were QFT negative (top panels) or QFT positive (bottom panels) at screening. Horizontal lines represent medians, boxes the IQR, and whiskers the range. p values were computed by generalised estimating equation (GEE) linear regression assessing the difference between each timepoint after vaccination relative to before vaccination (day 0). Values were adjusted for multiple testing using the Holm method. Only p values lower than 0·1 are shown. The percentage of responders (bottom of the graphs) at each timepoint was computed using COMPASS, relative to baseline to take into account the fact that populations were non-naive at baseline because of either previous BCG vaccination at birth or previous Mycobacterium tuberculosis exposure for QFT-positive groups (appendix p 14). (C, D) Median longitudinal trajectories of CD4 (C) and CD8 (D) T-cell frequencies expressing any combination of IFN-γ, IL-2, TNF, IL-17A, or IL-22 (C top panels and D) or co-expressing IFN-γ, IL-2, and TNF (C, bottom panels) in participants who were QFT negative (left) and QFT positive (right), stratified by treatment group and dose at the indicated timepoints. p values between cohorts were calculated using the Kruskal-Wallis test. Error bars denote IQRs. Frequencies of cytokine-positive CD4 T cells in the unstimulated control were subtracted from MTBVAC-stimulated frequencies. CFU=colony-forming unit. IFN=interferon. IL=interleukin. MTBVAC=live-attenuated M tuberculosis vaccine. NA=not applicable. QFT=QuantiFERON-tuberculosis Gold-Plus assay. TNF=tumour necrosis factor.

Figure 4:. IFN-γ responses measured by QFT in individuals vaccinated with different doses of MTBVAC or BCG who were QFT negative at screening

IFN-γ concentrations (IU/mL) measured by QFT, either stratified by timepoints (A) or vaccine group (MTBVAC dose or BCG) at the indicated timepoints after vaccination (B). The higher IFN-γ concentration between TB1 and TB2, after subtracting the Nil condition, is shown. The dotted horizontal lines indicate the QFT positivity cutoff (0·35 IU/mL). Horizontal lines represent medians, boxes the IQR, and whiskers the range. The percentage of participants who were QFN positive at each timepoint for each cohort is indicated below each graph. All day 84 visits in the 5 × 10⁶ CFU MTBVAC group were missed because of the COVID-19 lockdown in South Africa. IFN=interferon. MTBVAC=live-attenuated M tuberculosis vaccine. QFT=QuantiFERON-tuberculosis Gold-Plus assay.