Vaccines to protect against tuberculosis (TB) are urgently needed. We performed a case–control analysis to identify immune correlates of TB disease risk in Bacille Calmette–Guerin (BCG) immunized infants from the MVA85A efficacy trial. Among 53 TB case infants and 205 matched controls, the frequency of activated HLA-DR+ CD4+ T cells associates with increased TB disease risk (OR=1.828, 95% CI=1.25–2.68, P=0.002, FDR=0.04, conditional logistic regression). In an independent study of Mycobacterium tuberculosis-infected adolescents, activated HLA-DR+ CD4+ T cells also associate with increased TB disease risk (OR=1.387, 95% CI=1.068–1.801, P=0.014, conditional logistic regression). In infants, BCG-specific T cells secreting IFN-γ associate with reduced risk of TB (OR=0.502, 95% CI=0.29–0.86, P=0.013, FDR=0.14). The causes and impact of T-cell activation on disease risk should be considered when designing and testing TB vaccine candidates for these populations.

Background. A new vaccine is urgently needed to combat tuberculosis. However, without a correlate of protection, selection of the vaccines to take forward into large-scale efficacy trials is difficult. Use of bacille Calmette-Guérin (BCG) as a surrogate for human Mycobacterium tuberculosis challenge is a novel model that could aid selection.Methods. Healthy adults were assigned to groups A and B (BCG-naive) or groups C and D (BCG-vaccinated). Groups B and D received candidate tuberculosis vaccine MVA85A. Participants were challenged with intradermal BCG 4 weeks after those who received MVA85A. Skin biopsies of the challenge site were taken 2 weeks post challenge and BCG load quantified by culture and quantitative polymerase chain reaction (qPCR).Results. Volunteers with a history of BCG showed some degree of protective immunity to challenge, having lower BCG loads compared with volunteers without prior BCG, regardless of MVA85A status. There was a significant inverse correlation between antimycobacterial immunity at peak response after MVA85A and BCG load detected by qPCR.Conclusion. Our results support previous findings that this BCG challenge model is able to detect differences in antimycobacterial immunity induced by vaccination and could aid in the selection of candidate tuberculosis vaccines for field efficacy testing.Clinical Trials Registration NCT01194180.

SummaryThe efficacy of Bacillus Calmette-Guerin (BCG) vaccination in protection against pulmonary tuberculosis (TB) is highly variable between populations. One possible explanation for this variability is increased exposure of certain populations to non-tuberculous mycobacteria (NTM). This study used a murine model to determine the effect that exposure to NTM after BCG vaccination had on the efficacy of BCG against aerosol Mycobacterium tuberculosis challenge. The effects of administering live Mycobacterium avium (MA) by an oral route and killed MA by a systemic route on BCG-induced protection were evaluated. CD4+ and CD8+ T cell responses were profiled to define the immunological mechanisms underlying any effect on BCG efficacy. BCG efficacy was enhanced by exposure to killed MA administered by a systemic route; T helper 1 and T helper 17 responses were associated with increased protection. BCG efficacy was reduced by exposure to live MA administered by the oral route; T helper 2 cells were associated with reduced protection. These findings demonstrate that exposure to NTM can induce opposite effects on BCG efficacy depending on route of exposure and viability of NTM. A reproducible model of NTM exposure would be valuable in the evaluation of novel TB vaccine candidates.

Development of an improved vaccine against tuberculosis (TB) is hindered by the lack of a surrogate of protection. Efficacy of new TB vaccines in humans can only be evaluated by expensive and time consuming efficacy trials within TB endemic areas. It is critical that vaccines with the greatest potential to protect are selected for these trials. Mycobacterial growth inhibition assays (MGIAs) have been developed with the hope that these in-vitro functional assays will correlate with protection, which could aid in the selection of the best vaccine candidates. The present study describes the use of the BACTEC system to perform MGIAs in mice. We demonstrate reproducible mycobacterial growth inhibition in splenocytes from BCG immunised mice compared with unimmunised mice (P < 0.023), which corresponded with in-vivo efficacy against Mycobacterium tuberculosis (M. tb) challenge. Microarray data showed extensive differential gene expression in splenocyte responses to ex-vivo BCG stimulation between unimmunised and BCG-immunised mice. TH1 responses, including IFN-γ, nitric oxide synthase (NOS2) and Interleukin -17 (IL-17) expression were enhanced in BCG immunised mice, indicating a possible mechanism for mycobacterial growth inhibition. Further investigation into whether the BACTEC MGIA can be used as a surrogate of protection in humans and preclinical animal models is now warranted.

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SummaryObjectivesOuter membrane vesicle (OMV) vaccines are used against outbreaks of capsular group B Neisseria meningitidis (MenB) caused by strains expressing particular PorA outer membrane proteins (OMPs). Ferric enterobactin receptor (FetA) is another variable OMP that induces type-specific bactericidal antibodies, and the combination of judiciously chosen PorA and FetA variants in vaccine formulations is a potential approach to broaden protection of such vaccines.MethodsThe OMV vaccine MenPF-1 was generated by genetically modifying N. meningitidis strain 44/76 to constitutively express FetA. Three doses of 25 μg or 50 μg of MenPF-1 were delivered intra-muscularly to 52 healthy adults.ResultsMenPF-1 was safe and well tolerated. Immunogenicity was measured by serum bactericidal assay (SBA) against wild-type and isogenic mutant strains. After 3 doses, the proportion of volunteers with SBA titres ≥1:4 (the putative protective titre) was 98% for the wild-type strain, and 77% for the strain 44/76 FetAonPorAoff compared to 51% in the strain 44/76 FetAoffPorAoff, demonstrating that vaccination with MenPF-1 simultaneously induced FetA and PorA bactericidal antibodies.ConclusionThis study provides a proof-of-concept for generating bactericidal antibodies against FetA after OMV vaccination in humans. Prevalence-based choice of PorA and FetA types can be used to formulate a vaccine for broad protection against MenB disease.

Immune activation is associated with increased risk of tuberculosis (TB) disease in infants. We performed a case-control analysis to identify drivers of immune activation and disease risk. Among 49 infants who developed TB disease over the first two years of life, and 129 matched controls who remained healthy, we found the cytomegalovirus (CMV) stimulated IFN-γ response at age 4-6 months to be associated with CD8+ T-cell activation (Spearman’s rho, p=6×10−8). A CMV specific IFN-γ response was also associated with increased risk of developing TB disease (Conditional Logistic Regression, p=0.043, OR 2.2, 95% CI 1.02-4.83), and shorter time to TB diagnosis (Log Rank Mantel-Cox p=0.037). CMV positive infants who developed TB disease had lower expression of natural killer cell associated gene signatures and a lower frequency of CD3-CD4-CD8-lymphocytes. We identified transcriptional signatures predictive of risk of TB disease among CMV ELISpot positive (AUROC 0.98, accuracy 92.57%) and negative (AUROC 0.9, accuracy 79.3%) infants; the CMV negative signature validated in an independent infant study (AUROC 0.71, accuracy 63.9%). Understanding and controlling the microbial drivers of T cell activation, such as CMV, could guide new strategies for prevention of TB disease in infants.

Outer membrane vesicle (OMV)- based vaccines have been used to provide strain-specific protection against capsular group B Neisseria meningitidis infections, but the full breadth of the immune response against the components of the OMV has not been established. Sera from adults vaccinated with an OMV vaccine were used to screen 91 outer membrane proteins (OMPs) incorporated in an antigen microarray panel. Antigen-specific IgG levels were quantified pre-vaccination, and after 12 and 18 weeks. These results were compared with IgG levels from mice vaccinated with the same OMV vaccine. The repertoires of highly responding antigens in humans and mice overlapped, but were not identical. The highest responding antigens to human IgG comprised four integral OMPs (PorA, PorB, OpcA and PilQ), a protein which promotes the stability of PorA and PorB (RmpM) and two lipoproteins (BamC and GNA1162). These observations will assist in evaluating the role of minor antigen components within OMVs in providing protection against meningococcal infection. In addition, the relative dominance of responses to integral OMPs in humans emphasizes the importance of this subclass and points to the value of maintaining conformational epitopes from integral membrane proteins in vaccine formulations.