Tuberculosis vaccine H56IC(Statens Serum Institute)

People with tuberculosis who complete treatment remain at risk of recurrent disease. The vaccine H56:IC31 has been shown to be safe and immunogenic in phase 1 and 2 studies, but whether it can reduce the risk of tuberculosis recurrence is unknown.

In a double-blind, randomised, placebo-controlled, phase 2b trial in South Africa (five clinical trial sites) and Tanzania (one clinical trial site), we enrolled participants aged 18-60 years, without HIV, who had completed more than 5 months (22 weeks) of treatment for drug-susceptible pulmonary tuberculosis. During trial screening (≤7 days after starting treatment), two sputum samples were obtained and frozen for later comparison to recurrent isolates by whole-genome sequencing (WGS). Eligible participants were randomly assigned (1:1; block size of four) to receive two intramuscular doses in the deltoid, 56 days apart, of H56:IC31 or placebo. After the first dose of H56:IC31 or placebo, participants were followed up until study day 421 (1 year after the second dose) and checked at each visit for tuberculosis signs and symptoms. If tuberculosis was suspected, two sputum samples were obtained: one sample was tested by automated molecular test (Xpert MTB/RIF Ultra) and sent for liquid culture; and the other sample was stored frozen for later analysis by whole-genome sequencing (WGS). At the last visit (day 421), two sputum samples were obtained from all sputum-productive participants, regardless of symptoms, to detect cases of asymptomatic tuberculosis. The primary endpoint was culture-confirmed recurrent pulmonary tuberculosis (due to relapse with the same strain, reinfection by a different strain, or indeterminate) occuring during the period starting at day 70 (14 days after the second dose) and ending on day 421 (1 year after the second dose). Vaccine efficacy against recurrent tuberculosis was derived from Cox proportional hazards models. Secondary endpoints included vaccine efficacy to prevent tuberculosis relapse or reinfection independently, as differentiated by WGS, and safety and immunogenicity outcomes (H56-specific CD4 T-cell responses and humoral anti-H56 IgG responses). Primary analysis of vaccine efficacy was based on modified intention-to-treat (mITT), in all randomly assigned participants except those with tuberculosis disease recurrence or who withdrew before day 70 (or 14 days after the second dose for those who received both doses). Safety was assessed in all randomly assigned participants who received at least one dose of vaccine or placebo. The trial was registered with ClinicalTrials.gov, NCT03512249, and is complete.

831 participants (mean age 34·7 years [SD 11·1]; 229 [28%] female and 602 [72%] male; 549 [66%] Black) were enrolled from Jan 31, 2019, to Jan 20, 2022; 415 participants were randomly assigned to receive H56:IC31 and 416 to receive placebo. Follow-up was completed by March 20, 2023 (mean follow-up duration 410·1 days [SD 82·8]). In the primary mITT analysis, recurrent tuberculosis occurred in 23 of 400 participants in the H56:IC31 group (12 relapses, eight reinfections, and three indeterminate); and in 14 of 406 in the placebo group (six relapses, seven reinfections, and one indeterminate). Vaccine efficacy for prevention of recurrence was -73·8% (95% CI -246·9 to 9·8; p=0·10). Vaccine efficacy for prevention of relapse was -116·1% (-522·2 to 16·3; p=0·11) and for prevention of reinfection was -21·1% (-245·3 to 56·5; p=0·71). 2 weeks after the planned second dose, H56:IC31 had significantly increased the frequencies of H56-specific CD4 T cells expressing interferon-γ, tumour necrosis factor, interleukin (IL)-2, or IL-17 in vaccinees (median percentage of CD4 T cells, 0·35% [IQR 0·19 to 0·57]) compared with placebo (0·11% [0·09 to 0·23]; p<0·0001). H56-specific IgG responses were significantly higher in H56:IC31 recipients (median arbitrary units per mL, 6·84 [IQR 1·64 to 32·8]) than in placebo recipients (1·94 [1·05 to 3·86]; p<0·0001). A greater proportion of H56:IC31 recipients had mild-to-moderate injection site reactions than placebo recipients (165 [40%] of 415 vs 78 [19%] of 416). No treatment-related serious adverse events were reported. Two participants who received H56:IC31 and six who received placebo died.

Vaccination with H56:IC31 at treatment completion for pulmonary tuberculosis did not reduce the risk of recurrent disease. H56:IC31 was well tolerated and immunogenic but might have increased the risk of relapses by endogenous strains.

The European and Developing Countries Clinical Trials Partnership (EDCTP2) supported by the EU (grant number RIA2016V-1631, POR TB consortium). Additional funding to support completion of the trial was provided by the Statens Serum Institut, Aurum Institute, and the South African Tuberculosis Vaccine Initiative.

H56:IC31 is a candidate vaccine against tuberculosis (TB) with the potential to reduce TB recurrence rate. It is thus important for future clinical trials to demonstrate safety and immunogenicity of H56:IC31 in individuals treated for TB.

Twenty-two adults confirmed to be Mycobacterium tuberculosis negative (by 2 GeneXpert tests or 2 sputum cultures) after 4–5 months of TB treatment, and not more than 28 days after completion of TB treatment, were randomized to receive 2 doses of H56:IC31 (5 mg H56:500 nmol IC31; n = 16) or placebo (n = 6) 56 days apart. Participants were followed for 420 days for safety and immunogenicity.

H56:IC31 vaccination was associated with an acceptable safety profile, consisting mostly of mild self-limited injection site reactions. No serious adverse events or vaccine-related severe adverse events were reported. H56:IC31 induced a CD4+ T-cell response for Ag85B and ESAT-6, with ESAT-6 being immunodominant, which persisted through 6 months after the last vaccination. There was some evidence of CD8+ T-cell responses for both Ag85B and ESAT-6, but to a lesser extent than CD4+ responses.

H56:IC31 was associated with an acceptable safety profile, and induced a predominant CD4+ T-cell response, in adults recently treated for drug-susceptible, uncomplicated pulmonary TB.

NCT02375698.