Diagnostic Accuracy of Early Secretory Antigenic Target-6-Free Interferon-gamma Release Assay Compared to QuantiFERON-TB Gold In-tube

Timing of maternal isoniazid preventive therapy on tuberculosis infection among infants exposed to HIV in low-income and middle-income settings: a secondary analysis of the TB APPRISE trial

BACKGROUND

Infants born to women with HIV in settings with a high tuberculosis burden are at risk of tuberculosis infection and rapid progression to active disease. Maternal isoniazid preventive therapy might mitigate this risk, but optimal timing of therapy remains unclear. The TB APPRISE trial showed that initiation of isoniazid during pregnancy resulted in more frequent adverse pregnancy outcomes than when initiated postpartum. We aimed to determine the proportion of infants testing positive for tuberculosis infection born to mothers who initiated isoniazid therapy antepartum compared with postpartum using two commonly used tests, the test agreement, and predictors of test positivity.

METHODS

TB APPRISE was a randomised, double-blind, placebo-controlled, non-inferiority trial done at 13 study sites across eight countries (Botswana, Haiti, India, South Africa, Tanzania, Thailand, Uganda, and Zimbabwe). Pregnant women with HIV on antiretroviral therapy were randomly assigned to receive immediate isoniazid preventive therapy (28 weeks isoniazid [300 mg daily], then placebo until week 40 after delivery) or deferred treatment (placebo until week 12 after delivery, then isoniazid [300 mg daily] for 28 weeks). Mother-infant pairs were followed up until 48 weeks after delivery. We included all liveborn infants with a tuberculin skin test or interferon-γ release assay (IGRA) at 44 weeks. The outcomes assessed in this secondary analysis were tuberculosis test positivity by study group, test agreement, and predictors of test positivity. This study was registered with ClinicalTrials.gov, NCT01494038.

FINDINGS

Between Aug 19, 2014, and April 4, 2016, 956 mothers were randomly assigned, and 749 mother-child pairs were included in this secondary analysis. Of 749 infants, 694 (93%) received Bacille Calmette-Guérin (BCG) vaccination, 675 (90%) were born to mothers who had completed isoniazid treatment, 20 (3%) were exposed to tuberculosis, seven (1%) became HIV positive, and one (<1%) developed probable tuberculosis. 43 (6%; 95% CI 4-8]) of 732 infants had a positive IGRA test result and 55 (8%; 6-10) of 727 infants had a positive tuberculin skin test result. Test positivity did not differ by study group (p=0·88 for IGRA; p=0·44 for tuberculin skin test). Test agreement was poor (κ=0·107 [95% CI 0·002-0·212]). Infant tuberculin skin test positivity was associated with breastfeeding (adjusted odds ratio 6·63 [95% CI 1·57-27·9]), BCG vaccination (4·97 [1·50-16·43]), and maternal tuberculin skin test positivity at delivery (3·28 [1·70-6·33]); IGRA positivity was associated with female sex (2·09 [1·06-4·14]).

INTERPRETATION

Deferral of maternal isoniazid preventive therapy to early postpartum had no effect on infant tuberculosis acquisition in our trial population, regardless of the diagnostic test used; however, tuberculosis test agreement is poor during infancy.

FUNDING

US National Institutes of Health.

Synthesis of plant-based, self-adjuvanted, dual antigen specific to Mycobacterium tuberculosis as a novel tuberculosis subunit vaccine that elicits immunogenicity in rabbit

OBJECTIVES

The only approved vaccine, Bacillus Calmette Guérin (BCG) used in global tuberculosis (TB) immunization programmes has been very effective in childhood TB but not in adult pulmonary and latent TB. Moreover, the emergence of multi-drug resistance-TB cases demands either to increase efficiency of BCG or replace it with the one with improved efficacy.

RESULTS

A novel combination of two most effective secreted protein antigens specific for Mycobacterium tuberculosis (Mtb), ESAT-6 and MPT-64 (but not present in BCG strains) fused with a cholera toxin B subunit (CTB) and tagged with 6xHis was expressed for the first time in Escherichia coli as well as in transgenic cucumber plants developed using Agrobacterium tumefaciens-mediated transformation. The recombinant fusion protein (His6x.CTB-ESAT6-MPT64) expressed in E. coli was purified by a single-step affinity chromatography and used to produce polyclonal antibodies in rabbit. The transgenic cucumber lines were confirmed by polymerase chain reaction (PCR), Southern blot hybridization, reverse transcriptase PCR (RT-PCR), real-time PCR (qRT-PCR) and expression of recombinant fusion protein by western blot analysis and its quantification by enzyme-linked immunosorbent assay (ELISA). A maximum value of the fusion protein, 478 ng.g^-1 (0.030% of the total soluble protein) was obtained in a transgenic cucumber line. Rabbit immunized orally showed a significant increase in serum IgG levels against the fusion protein as compared to the non-immunized rabbit.

CONCLUSIONS

Stable expression of Mtb antigens with CTB in edible cucumber plants (whose fruits are eaten raw) in sufficient amount possibly would facilitate development of a safe, affordable and orally delivered self-adjuvanted, novel dual antigen based subunit vaccine against TB.

End-point definition and trial design to advance tuberculosis vaccine development

Tuberculosis (TB) remains a leading infectious cause of death worldwide and the coronavirus disease 2019 pandemic has negatively impacted the global TB burden of disease indicators. If the targets of TB mortality and incidence reduction set by the international community are to be met, new more effective adult and adolescent TB vaccines are urgently needed. There are several new vaccine candidates at different stages of clinical development. Given the limited funding for vaccine development, it is crucial that trial designs are as efficient as possible. Prevention of infection (POI) approaches offer an attractive opportunity to accelerate new candidate vaccines to advance into large and expensive prevention of disease (POD) efficacy trials. However, POI approaches are limited by imperfect current tools to measure Mycobacterium tuberculosis infection end-points. POD trials need to carefully consider the type and number of microbiological tests that define TB disease and, if efficacy against subclinical (asymptomatic) TB disease is to be tested, POD trials need to explore how best to define and measure this form of TB. Prevention of recurrence trials are an alternative approach to generate proof of concept for efficacy, but optimal timing of vaccination relative to treatment must still be explored. Novel and efficient approaches to efficacy trial design, in addition to an increasing number of candidates entering phase 2-3 trials, would accelerate the long-standing quest for a new TB vaccine.

Prevalence of Mycobacterium tuberculosis infection as measured by the QuantiFERON-TB Gold assay and ESAT-6 free IGRA among adolescents in Mwanza, Tanzania

Background

The prevalence of latent tuberculosis infection (LTBI) is vastly higher than that of tuberculosis (TB) disease and this enormous reservoir of individuals with LTBI impacts the global TB control strategy. Adolescents are at greatest risk of TB infection and are thus an ideal target population for a potential effective TB vaccine to be added to the current BCG programme as it could reduce the number of latent infections and consequently the number of adults with TB disease. However, LTBI rates are often unknown for this population. This study aims to estimate the magnitude of LTBI and to determine if Tanzanian adolescents would be a good population for a prevention of TB infection trial.

Methods

This was a descriptive cross-sectional study that recruited 193 adolescents aged 12 and 16 years from government schools and directly from the community in Mwanza Region, Tanzania. Socio-demographic characteristics were collected for all enrolled participants. Blood was drawn and tested using QuantiFERON-TB Gold In-Tube (QFT-GIT), and Early Secretory Antigenic Target-6–Free Interferon-gamma Release Assay (ESAT-6 free IGRA). Concordance between QFT-GIT and ESAT-6 free IGRA was evaluated using the McNemar’s test.

Results

Overall estimates of LTBI prevalence were 19.2% [95%CI, 14.1; 25.2] and 18.6% [95%CI, 13.6; 24.6] as measured by QFT-GIT IGRA and ESAT-6 free IGRA, respectively. The 16-year-old cohort had a higher LTBI prevalence (23.7% [95%CI, 16.1; 32.9]) as compared to 12-year-old cohort (14.6% [95%CI, 8.6; 22.7]) as measured by QFT-GIT IGRA. When measured by ESAT-6 Free IGRA, LTBI prevalence was 24.7% (95%CI, 16.9; 34.0) for the 16-year-old cohort and 12.5% (95%CI, 7.0; 20.3) among the 12-year-old cohort. According to both tests the prevalence of TB infection and the corresponding annual risk of tuberculosis infection (ARTI) and force of infection were high and increased with age. Of all enrolled participants, 97.4% had concordant results for QFT-GIT IGRA and ESAT-6 free IGRA (p = 0.65).

Conclusions

The prevalence of LTBI and the associated ARTI and force of infection among adolescents is high and increases with age in Mwanza Region. There was a high concordance between the QFT-GIT and the novel ESAT-6 free IGRA assays. These findings suggest Mwanza is a promising area to conduct novel TB vaccine research prevention of infection (POI) studies targeting adolescents.

Screening for Mycobacterium tuberculosis Infection Using Beijing/K Strain-Specific Peptides in a School Outbreak Cohort

Background

The Beijing strain of Mycobacterium tuberculosis (M. tb) has been most frequently isolated from TB patients in South Korea, and the hyper-virulent Beijing/K genotype is associated with TB outbreaks. To examine the diagnostic potential of Beijing/K-specific peptides, we performed IFN-γ release assays (IGRA) using a MTBK antigen tube containing Beijing/K MTBK_24800, ESAT-6, and CFP-10 peptides in a cohort studied during a school TB outbreak.

Methods

A total of 758 contacts were investigated for M. tb infection, and 43 contacts with latent TB infection (LTBI) and 25 active TB patients were enrolled based on serial screening with QuantiFERON-TB Gold In-Tube tests followed by clinical examinations. Blood collected in MTBK antigen tubes was utilized for IGRA and multiplex cytokine bead arrays. Immune responses were retested in 24 patients after TB treatment, and disease progression was investigated in subjects with LTBI.

Results

Total proportions of active disease and LTBI during the outbreak were 3.7% (28/758) and 9.2% (70/758), respectively. All clinical isolates had a Beijing/K M. tb genotype. IFN-γ responses to the MTBK antigen identified M. tb infection and distinguished between active disease and LTBI. After anti-TB treatment, IFN-γ responses to the MTBK antigen were significantly reduced, and strong TNF-α responses at diagnosis were dramatically decreased.

Conclusions

MTBK antigen-specific IFN-γ has diagnostic potential for differentiating M. tb infection from healthy controls, and between active TB and LTBI as well. In addition, TNF-α is a promising marker for monitoring therapeutic responses. These data provide informative readouts for TB diagnostics and vaccine studies in regions where the Beijing/K strain is endemic.

Diagnostic benefits of adding EspC, EspF and Rv2348-B to the QuantiFERON Gold In-tube antigen combination

Interferon (IFN)-γ release assays (IGRAs) are used to diagnose latent tuberculosis (TB) infection (LTBI). To improve the accuracy of these tests, different approaches, such as alternative cytokine detection and using different antigens, are considered. Following this purpose, this study aims to evaluate the addition of EspC, EspF and Rv2348-B to those present in the QuantiFERON-TB Gold In-Tube (QFN-G-IT). We included 115 subjects: 74 active TB patients, 17 LTBI individuals and 24 healthy controls. Whole blood samples were collected in QFN-G-IT and in-house tubes containing different combinations of EspC, EspF and Rv2348-B, together with ESAT-6, CFP-10, and TB7.7. After overnight incubation at 37 ºC, plasma was harvested and IFN-γ quantified. IFN-γ levels in the QFN-G-IT and in-house tubes correlated very good (Spearman Rho(r) > 0.86). In-house antigen combinations distinguished healthy individuals from those with active TB and LTBI (specificities and sensitivities higher than 87.5% and 96.3%, respectively [AUC > 0.938]). Adding EspC, EspF and Rv2348-B, increased the sensitivity of the test, being the addition of EspC and Rv2348-B the combination that yielded a higher sensitivity with no specificity loss. Addition of these antigens could improve diagnosis in patients with impaired or immature immune response who are at high risk of developing TB.

Clinical Development of New TB Vaccines: Recent Advances and Next Steps

Mycobacterium tuberculosis (Mtb) kills more people worldwide than any single infectious pathogen, yet the only vaccine licensed against tuberculosis, Bacille Calmette Guerin (BCG) is approaching its centenary. Two recent advances in clinical tuberculosis vaccine development have invigorated the field. BCG revaccination of interferon-gamma release assay (IGRA) negative adolescents provided 45% protection against sustained Mtb infection defined by IGRA conversion; and the protein-subunit vaccine M72/AS01_E provided 50% protection against progression from Mtb infection to tuberculosis disease in IGRA-positive adults. These findings provide encouraging evidence for pre-exposure and post-exposure approaches to vaccination against tuberculosis, both of which may be necessary to rapidly interrupt the cycle of Mtb transmission and sustain long-term impact on global tuberculosis control. New trials are needed to demonstrate efficacy of M72/AS01_E with greater precision, in a wider age range, in diverse epidemic settings, and in populations that include Mtb-uninfected and HIV-infected persons. Modeling the impact of mass campaigns with M72/AS01_E and other fast-follower vaccine candidates will be crucial to make the use case and demonstrate public health value for TB endemic countries. The size and scope of the next generation of efficacy trials, and the need to expand and accelerate the existing clinical development pipeline, will require public and private consortium funding and concerted political will.

Expression of ESAT-6 antigen from Mycobacterium tuberculosis in broccoli: An edible plant

Tuberculosis (TB) is one of the major infectious diseases caused by Mycobacterium tuberculosis. The development of an effective and economical vaccine for controlling TB is essential especially for developing countries. Edible plants can serve as biofactories to produce vaccine antigens. In this study, 6 kDa early secretory antigenic target (ESAT-6) of M. tuberculosis was expressed in Brassica oleracea var. italica via Agrobacterium-mediated transformation to facilitate oral delivery of antigen. ESAT-6 gene was cloned using Gateway® cloning strategy. Transformation and presence of transgene was confirmed through PCR. Expression level of transgene was calculated via quantitative real-time PCR (qRT-PCR) and the maximum integrated transgene number was two. Maximum amount of total soluble fraction of ESAT-6 was evaluated by immunoblotting, estimated to accumulate up to 0.5% of total soluble protein. The recombinant ESAT-6 protein was further purified and detected using silver staining and Western blotting. ESAT-6 protein induced humoral immune response in mice immunized orally and subcutaneously. The expression of M. tuberculosis antigen in edible plants could aid in the development of cost-effective and oral delivery of an antigen-based subunit vaccine against TB. To the best our knowledge, it is the first report of expression of a vaccine antigen in broccoli.

Chloroplast-based inducible expression of ESAT-6 antigen for development of a plant-based vaccine against tuberculosis

Mycobacterium tuberculosis causes tuberculosis in humans. The major disease burden of tuberculosis lies in developing countries. Lack of an effective vaccine for adults is one of the major hurdles for controlling this deadly disease. In the present study, 6 kDa early secretory antigenic target (ESAT-6) of M. tuberculosis was inducibly expressed in chloroplasts of Nicotiana tabacum. The expression of ESAT-6 in chloroplasts was controlled by T7 promoter that was activated by nuclear-generated signal peptide. Tobacco plants, containing nuclear component, were transformed via biolistic bombardment with pEXP-T7-ESAT-6 obtained by Gateway® cloning. Transformation and homoplasmic status of transplastomic plants was confirmed by polymerase chain reaction and Southern blotting. Plants were induced for protein expression by spraying with 5% ethanol for 1 day, 3 days, 7 days and 10 days. ESAT-6 protein was detected by immunoblot analysis and maximum protein was obtained for 10 days induced plants that was estimated to accumulate up to 1.2% of total soluble fraction of protein. Transplastomic plants showed completely normal morphology. Transplastomic and untransformed plants became slightly chlorotic upon prolonged exposure to ethanol until 10 days. Taken together, this data could help in the development of an antigen-based subunit vaccine against tuberculosis.

Recombinant production of ESAT-6 antigen in thermoinducible Escherichia coli: the role of culture scale and temperature on metabolic response, expression of chaperones, and architecture of inclusion bodies

The heat-inducible expression system has been widely used to produce recombinant proteins in Escherichia coli. However, the rise in temperature affects cell growth, activates the bacterial Heat-Shock Response (HSR), and promotes the formation of insoluble protein aggregates known as inclusion bodies (IBs). In this work, we evaluate the effect of the culture scale (shake flasks and bioreactors) and induction temperature (39 and 42 °C) on the kinetic behavior of thermoinducible recombinant E. coli ATCC 53606 producing rESAT-6 (6-kDa early-secretory antigenic target from Mycobacterium tuberculosis), compared with cultures grown at 30 °C (without induction). Also, the expression of the major E. coli chaperones (DnaK and GroEL) was analyzed. We found that almost twice maximum biomass and rESAT-6 production were obtained in bioreactors (~ 3.29 g/L of biomass and ~ 0.27 g/L of rESAT-6) than in shake flasks (~ 1.41 g/L of biomass and ~ 0.14 g/L of rESAT-6) when induction was carried out at 42 °C, but similar amounts of rESAT-6 were obtained from cultures induced at 39 °C (~ 0.14 g/L). In all thermo-induced conditions, rESAT-6 was trapped in IBs. Furthermore, DnaK was preferably expressed in the soluble fraction, while GroEL was present in IBs. Importantly, IBs formed at 39 °C, in both shake flasks and bioreactors, were more susceptible to degradation by proteinase-K, indicating a lower amyloid content compared to IBs formed at 42 °C. Our work presents evidence that the culture scale and the induction temperature modify the E. coli metabolic response, expression of chaperones, and structure of the IBs during rESAT-6 protein production in a thermoinducible system.