Live-attenuated Mycobacterium tuberculosis vaccine MTBVAC versus BCG in adults and neonates: a randomised controlled, double-blind dose-escalation trial

Background: Infants are a key target population for new tuberculosis vaccines. We assessed the safety and immunogenicity of the live-attenuated Mycobacterium tuberculosis vaccine candidate MTBVAC in adults and infants in a region where transmission of tuberculosis is very high. Methods: We did a randomised, double-blind, BCG-controlled, dose-escalation trial at the South African Tuberculosis Vaccine Initiative site near Cape Town, South Africa. Healthy adult community volunteers who were aged 18–50 years, had received BCG vaccination as infants, were HIV negative, had negative interferon-¿ release assay (IGRA) results, and had no personal history of tuberculosis or current household contact with someone with tuberculosis were enrolled in a safety cohort. Infants born to HIV-negative women with no personal history of tuberculosis or current household contact with a person with tuberculosis and who were 96 h old or younger, generally healthy, and had not yet received routine BCG vaccination were enrolled in a separate infant cohort. Eligible adults were randomly assigned (1:1) to receive either BCG Vaccine SSI (5 × 105 colony forming units [CFU] of Danish strain 1331 in 0·1 mL diluent) or MTBVAC (5 × 105 CFU in 0·1 mL) intradermally in the deltoid region of the arm. After favourable review of 28-day reactogenicity and safety data in the adult cohort, infants were randomly assigned (1:3) to receive either BCG Vaccine SSI (2·5 × 105 CFU in 0·05 mL diluent) or MTBVAC in three sequential cohorts of increasing MTBVAC dose (2·5 × 103 CFU, 2·5 × 104 CFU, and 2·5 × 105 CFU in 0·05 mL) intradermally in the deltoid region of the arm. QuantiFERON-TB Gold In-Tube IGRA was done on days 180 and 360. For both randomisations, a pre-prepared block randomisation schedule was used. Participants (and their parents or guardians in the case of infant participants), investigators, and other clinical and laboratory staff were masked to intervention allocation. The primary outcomes, which were all measured in the infant cohort, were solicited and unsolicited local adverse events and serious adverse events until day 360; non-serious systemic adverse events until day 28 and vaccine-specific CD4 and CD8 T-cell responses on days 7, 28, 70, 180, and 360. Secondary outcomes measured in adults were local injection-site and systemic reactions and haematology and biochemistry at study day 7 and 28. Safety analyses and immunogenicity analyses were done in all participants who received a dose of vaccine. This trial is registered with ClinicalTrials.gov, number NCT02729571. Findings: Between Sept 29, 2015, and Nov 16, 2015, 62 adults were screened and 18 were enrolled and randomly assigned, nine each to the BCG and MTBVAC groups. Between Feb 12, 2016, and Sept 21, 2016, 36 infants were randomly assigned—eight to the BCG group, nine to the 2·5 × 103 CFU MTBVAC group, nine to the 2·5 × 104 CFU group, and ten to the 2·5 × 105 CFU group. Mild injection-site reactions occurred only in infants in the BCG and the 2·5 × 105 CFU MTBVAC group, with no evidence of local or regional injection-site complications. Systemic adverse events were evenly distributed across BCG and MTBVAC dose groups, and were mostly mild in severity. Eight serious adverse events were reported in seven vaccine recipients (one adult MTBVAC recipient, one infant BCG recipient, one infant in the 2·5 × 103 CFU MTBVAC group, two in the 2·5 × 104 CFU MTBVAC group, and two in the 2·5 × 105 CFU MTBVAC group), including one infant in the 2·5 × 103 CFU MTBVAC group treated for unconfirmed tuberculosis and one in the 2·5 × 105 CFU MTBVAC group treated for unlikely tuberculosis. One infant died as a result of possible viral pneumonia. Vaccination with all MTBVAC doses induced durable antigen-specific T-helper-1 cytokine-expressing CD4 cell responses in infants that peaked 70 days after vaccination and were detectable 360 days after vaccination. For the highest MTBVAC dose (ie, 2·5 × 105 CFU), these responses exceeded responses induced by an equivalent dose of the BCG vaccine up to 360 days after vaccination. Dose-related IGRA conversion was noted in three (38%) of eight infants in the 2·5 × 103 CFU MTBVAC group, six (75%) of eight in the 2·5 × 104 CFU MTBVAC group, and seven (78%) of nine in the 2·5 × 105 CFU MTBVAC group at day 180, compared with none of seven infants in the BCG group. By day 360, IGRA reversion had occurred in all three infants (100%) in the 2·5 × 103 CFU MTBVAC group, four (67%) of the six in the 2·5 × 104 CFU MTBVAC group, and three (43%) of the seven in the 2·5 × 105 CFU MTBVAC group. Interpretation: MTBVAC had acceptable reactogenicity, and induced a durable CD4 cell response in infants. The evidence of immunogenicity supports progression of MTBVAC into larger safety and efficacy trials, but also confounds interpretation of tests for M tuberculosis infection, highlighting the need for stringent endpoint definition. Funding: Norwegian Agency for Development Cooperation, TuBerculosis Vaccine Initiative, UK Department for International Development, and Biofabri

A quantitative analysis of complexity of human pathogen-specific CD4 T cell responses in healthy M. tuberculosis infected South Africans

Author Summary: Human pathogen-specific immune responses are tremendously complex and the techniques to study them ever expanding. There is an urgent need for a quantitative analysis and better understanding of pathogen-specific immune responses. Mycobacterium tuberculosis (Mtb) is one of the leading causes of mortality due to an infectious agent worldwide. Here, we were able to quantify the Mtb-specific response in healthy individuals with Mtb infection from South Africa. The response is highly diverse and 66 epitopes are required to capture 80% of the total reactivity. Our study also show that the majority of the identified epitopes are restricted by multiple HLA alleles. Thus, technical advances are required to capture and characterize the complete pathogen-specific response. This study demonstrates further that the approach combining identified epitopes into "megapools" allows capturing a large fraction of the total reactivity. This suggests that this technique is generally applicable to the characterization of immunity to other complex pathogens. Together, our data provide for the first time a quantitative analysis of the complex pathogen-specific T cell response and provide a new understanding of human infections in a natural infection setting

Characterization of CD4 T cell responses using epitope pools.

<p>(A) Gating strategy for ICS assay. SSC-A; Side-scatter area, FSC-A; Forward-scatter area, SSC-W; Side-scatter width, FSC-W; Forward-scatter width, LD; Live/Dead discrimination. (B) Percentage cytokine detected from CD3⁺CD4⁺ T cells in response to the pool of 66, 125 and 300 epitopes, as well as heat killed H37Rv Mtb lysate. Each dot represents one donor (n = 34) median ± interquartile range is indicated. (C) Percentage Epitope pool-specific (125 epitopes) IFNγ, TNFα, IL-2 and IL-22 production by CD3⁺CD4⁺ T cells expressing each of the fifteen possible combinations. Each dot represents one donor (n = 34) median ± interquartile range is indicated. (D) The fraction of the total cytokine response against each stimuli expressing each combination of cytokines (pie chart) and all 4, 3, 2 or 1 cytokine (outer circle).</p

Demographic characteristics of enrolled participants.

<p>Demographic characteristics of enrolled participants.</p

HLA genotype and phenotype frequencies, and proportions of identified epitope restrictions.

<p>HLA genotype and phenotype frequencies, and proportions of identified epitope restrictions.</p

Responses to TB Vaccine and IGRA antigens are highly IFNγ polarized.

<p>Responses to TB Vaccine and IGRA antigens are highly IFNγ polarized.</p

Determination of HLA restriction of Mtb epitopes using HLA-transfected cell lines.

<p>Representative examples showing determination of HLA restriction for two epitopes in three donors. (A-C) PBMCs were incubated with peptide-pulsed cell lines transfected with each individual HLA molecule that matched the HLA alleles of the PBMC donor. IFNγ release was measured by ELISPOT. Positive responses (black bars, p<0.05), negative responses (white bars). N/A indicates cell line not available for the HLA allele.</p

Breadth and dominance of T cell epitopes in Mtb antigens.

<p>(A) All epitopes (n = 125) as a percentage of the total magnitude of response ranked on the basis of magnitude of T cell response and the 66 epitopes identified from TB vaccine and IGRA antigens and previously described epitopes. The dotted line indicates the 66 most immunodominant epitopes. (B) Proportion of the 63 donors who respond to the indicated number of epitopes of the top 66 identified epitopes.</p

Hierarchy in T cell reactivity against TB Vaccine and IGRA antigens.

<p>Magnitude of responses, expressed as the total magnitude of response (black bars, left y-axis) or frequency of donors responding (grey bars, right y-axis), amongst the 63 donors. Rv number and synonyms for each antigen are indicated on the x-axis. Antigens were divided into protein categories as defined by Tuberculist [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005760#ppat.1005760.ref036" target="_blank">36</a>]. All five antigens that are part of the cell wall and cell processes category are involved in the type VII secretion system [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005760#ppat.1005760.ref037" target="_blank">37</a>].</p