TB Vaccine Trial Research Articles

Reply to McShane.

Reply to McShane.

Development of a TB vaccine trial site in Africa and lessons from the Ebola experience

Tuberculosis is the deadliest infection of our time. In contrast, about 11,000 people died of Ebola between 2014 and 2016. Despite this manifest difference in mortality, there is now a vaccine licensed in the United States and by the European Medicines Agency, with up to 100% efficacy against Ebola. The developments that led to the trialing of the Ebola vaccine were historic and unprecedented. The single licensed TB vaccine (BCG) has limited efficacy. There is a dire need for a more efficacious TB vaccine. To deploy such vaccines, trials are needed in sites that combine high disease incidence and research infrastructure. We describe our twelve-year experience building a TB vaccine trial site in contrast to the process in the recent Ebola outbreak. There are additional differences. Relative to the Ebola pipeline, TB vaccines have fewer trials and a paucity of government and industry led trials. While pathogens have varying levels of difficulty in the development of new vaccine candidates, there yet appears to be greater interest in funding and coordinating Ebola interventions. TB is a global threat that requires similar concerted effort for elimination.

Development from a TB Vaccine Trial Site in Africa and Lessons from the Ebola Experience

Tuberculosis is the deadliest infection of our time, with about 1.3 million deaths in 2017. In contrast, about 11,000 people died of Ebola between 2014 and 2016. Despite this manifest difference in mortality, there is now a licensed vaccine with up to 100% efficacy against Ebola. The developments that led to the trialing and licensure of the Ebola vaccine were historic and unprecedented. The single licensed TB vaccine (BCG) has limited efficacy. There is a dire need for a new, more efficacious TB vaccine. In order to license and deploy such vaccines, trials are needed in a limited number of sites that combine high disease incidence, research infrastructure and expertise. We first chronologically describe our twelve-year experience in building a TB vaccine trial site, an arduous and incremental process in contrast to the recent Ebola outbreak, which illustrates that sites can be set up under great adversity. Due to the striking differences in the vaccine development of the two diseases, we also compare the number of respective human trials between the two diseases, using publicly available data. Relative to the Ebola pipeline, TB vaccines have fewer trials and a paucity of government and industry led trials. While acknowledging pathogens have varying levels of difficulty in the development of new vaccine candidates, there yet appears to be greater interest in funding and coordinating Ebola interventions. We are convinced that TB is a global threat that requires similar concerted effort for elimination. Funding Statement: AERAS, EDCTP and GSK funded the studies included in the manuscript. None had a role in interpreting results in the article or the decision to publish. Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: The authors stated that ethics approval was obtained for all the studies included, but was not applicable to this article.

In vitro Mycobacterial Growth Inhibition in South Korean Adults With Latent TB Infection.

Background: It is important to understand the ability to inhibit mycobacterial growth in healthy adults who would have been Bacillus Calmette-Guérin (BCG) vaccinated in childhood as this group will be the potential target population for novel booster TB vaccine trials. In this study we investigated not only the long-term immunity induced by childhood BCG vaccination but also protective immunity in terms of the ability to inhibit mycobacterial growth in those who were BCG vaccinated in childhood, with evidence of recent or remote TB infection.Methods: We measured the baseline immune response using a functional mycobacterial growth inhibition assay (MGIA) as a novel approach and an intracellular cytokine staining (ICS) assay as a reference approach in healthy adults, with different status of Mycobacterium tuberculosis (Mtb) infection.Results: Based on MGIA responses in historically BCG-vaccinated healthy adults, demographical characteristics including age, and gender did not affect mycobacterial growth inhibition in PBMC. However, the uninfected healthy control (HC) group showed a greater ability to inhibit mycobacterial growth compared with the latent TB infection (LTBI) group (P = 0.0005). In terms of the M. tuberculosis antigen-specific T-cell immune response in diluted whole blood quantitated using an ICS assay, the LTBI group had a higher frequency of polyfunctional CD 4+ T cells compared with the HC group (P = 0.0002), although there was no correlation between ICS and the MGIA assay.Conclusion: The Mtb infection status had a significant impact on mycobacterial growth inhibition in PBMC from healthy adults in South Korea, a country with an intermediate burden of tuberculosis, with healthy controls showing the greatest mycobacterial growth inhibition.

Optimisation of a functional mycobacterial growth-inhibition assay to improve its suitability for infant TB vaccine studies

The development of vaccines against tuberculosis continues to be hindered by the lack of correlates of protection. Immunity to Mycobacterium tuberculosis (M.tb) infection relies predominantly on cell mediated response, which is routinely measured using a read-out of host cytokine profiles. However, to date none of the cytokine profiles have been found to predict protection. A number of functional in vitro approaches that measure growth of mycobacteria pre- and post-vaccination as a potential functional surrogate marker for vaccine take have been developed. The use of a reporter-gene tagged BCG-lux assay measuring the viability of mycobacteria in whole blood samples has previously been described by our group to assess vaccine immunogenicity. Since only very small blood samples are usually available in paediatric studies, we now report a modification of the BCG-lux assay to reduce the volume required and make it more field-friendly. Our results show that a 2-fold reduction in blood volume made no significant difference to bacterial growth ratios, used as the main read-out. These results confirm the suitability of the BCG-lux assay for functional studies of vaccine immunogenicity and immunopathogenesis in young children and could play a role in late-phase TB vaccine trials of novel candidates.

Method for assessing IFN-γ responses in guinea pigs during TB vaccine trials

We sought to develop a new method that enables the assessment of the immune response of guinea pigs during TB vaccine evaluation studies, without the need to cull or anaesthetize animals. Guinea pigs were vaccinated with five different formulations of oral BCG. One week prior to challenge with Mycobacterium bovis, blood (50-200 μl) was taken from the ears of vaccinated subjects. Host RNA was isolated and amplified following antigenic restimulation of PBMCs for 24 h with 30 μg of bovine PPD. The up- or down-regulation of γ-interferon (IFN-γ), a key cytokine involved in protection against tuberculosis, was assessed using real-time PCR. The relative expression of prechallenge IFN-γ mRNA in the vaccinated groups (n=5) correlated (P<0·001) with protection against M. bovis challenge. We have demonstrated that it is possible to take blood samples and track IFN-γ responses in guinea pigs that then go on to be exposed to M. bovis, thus providing prechallenge vaccine uptake information. This methodology will also be applicable for tracking the immune responses of vaccinated guinea pigs over time that then go on to be challenged with M. tuberculosis during human TB vaccine evaluation studies.

Current Status of TB Vaccine Trials: Report of the eight new TB vaccine in clinical trials

We read with interest reports in Al Jazeera News(1) and Reuters News(2) of a new tuberculosis vaccine trial in South Africa and are pleased to learn that the Phase IIMVA85 A trial will begin shortly in the Western Cape, South Africa. The vaccine was developed by researchers at Oxford University and it works in tandem with BCG and acts as a booster to the older vaccine. Previous tests have already shown it produces a very high immune response but the key is to show it actually prevents disease. This vaccine passed Phase I clinical trials (Table 1) in Britain(3), and Africa (Gambia)(4), and is now starting Phase II clinical trials in Cape Town, South Africa(5). Although it is the first subunit TB vaccine that has entered clinical practice, it is NOT the first TB vaccine in clinical trials nor is it the first vaccine in Africa. This is the Second Vaccine in clinical trials and Second TB Vaccine in clinical trials in Africa(6). The MVA85A vaccine has just entered the Phase II clinical trials while an inactivated whole cell mycobacterial vaccine completed two Phase II clinical trials, one in Europe(7) (Finland) and the other in Africa(8) (Zambia) and also completed Phase III clinical trial in HIV+ve patients BCG primed in Africa(9).

Sputum microscopy for the diagnosis of HIV-associated pulmonary tuberculosis in Tanzania

BackgroundIn many resource poor settings only sputum microscopy is employed for the diagnosis of HIV-associated pulmonary tuberculosis; sputum culture may not be available.MethodsWe determined the diagnostic accuracy of sputum microscopy for active case finding of HIV-associated pulmonary tuberculosis using TB culture as the reference standard.Results2216 potential subjects screened for a TB vaccine trial submitted 9454 expectorated sputum specimens: 212 (2.2%) were sputum culture positive for Mycobacterium tuberculosis (MTB), 31 (0.3%) for non-tuberculous mycobacteria, and 79 (0.8%) were contaminated. The overall sensitivity of sputum microscopy was 61.8% (131/212) and specificity 99.7% (9108/9132). Sputum microscopy sensitivity varied from 22.6% in specimens with < 20 colony forming units (CFU)/specimen to 94.2% in patients with > 100 CFU/specimen plus confluent growth. The incremental diagnostic value for sputum microscopy was 92.1%, 1.8% and 7.1% for the first, second and third specimens, respectively. The positive predictive value and negative predictive values for sputum microscopy were 84.5% and 99.1%, respectively. The likelihood ratio (LR) of a positive sputum microscopy was 235.1 (95% CI 155.8 – 354.8), while the LR of a negative test was 0.38 (95CI 0.32 – 0.45). The 212 positive sputum cultures for MTB represented 103 patients; sputum microscopy was positive for 57 (55.3%) of 103 patients.ConclusionSputum microscopy on 3 expectorated sputum specimens will only detect 55% of culture positive HIV-infected patients in active screening for pulmonary tuberculosis. Sensitivity is higher in patients with greater numbers of CFUs in the sputum. Culture is required for active case finding of HIV- associated pulmonary tuberculosis.

Measuring Intracellular Mycobacterial Killing Using a Human Whole Blood Assay

Background : The mechanisms through which cellular activation results in intracellular mycobacterial killing is only partially understood. However, in vitro studies of human immunity to Mycobacterium tuberculosis have been largely modeled on the work reported by Crowle, which is complicated by several factors. The whole blood culture is simple and allows the simultaneous analysis of the relationship between bacterial killing and the effect of effector cells and humoral factors. In this study, we attempted to determine the extent to which M. tuberculosis is killed in a human whole blood culture and to explore the role of the host and microbial factor in this process. Methods : The PPD positive subject were compared to the umbilical cord blood and patients with tuberculosis, diabetes and lung cancer. The culture is performed using heparinized whole blood diluted with a culture medium and infected with a low number of M. avium or M. tuberculosis for 4 days by rotating the culture in a , 5% incubator. In some experiments, methlprednisolone- or pentoxifyline were used to inhibit the immune response. To assess the role of the T-cell subsets, CD4+, CD8+ T-cells or both were removed from the blood using magnetic beads. The log killing ratio was defined using a CFU assay as the difference in the log number of viable organisms in the completed culture compared to the inoculum. Results : 1. A trend was noted toward the improved killing of mycobacteria in PPD+ subjects comparing to the umbilical cord blood but there was no specific difference in the patients with tuberculosis, diabetes and lung cancer. 2. Methylprednisolone and pentoxifyline adversely affected the killing in the PPD+ subjects umbilical cord blood and patients with tuberculosis. 3. The deletion of CD4+ or CD8+ T-lymphocytes adversely affected the killing of M. avium and M. tuberculosis by PPD+ subjects. Deletion of both cell types had an additive effect, particularly in M. tuberculosis . 4. A significantly improved mycobacterial killing was noted after chemotherapy in patients with tuberculosis and the logKR continuously decreased in a 3 and 4 days of whole blood culture. Conclusion : The in vitro bactericidal assay by human whole blood culture model was settled using a CFU assay. However, the host immunity to M. tuberculosis was not apparent in the human whole blood culture bactericidal assay, and patients with tuberculosis showed markedly improved bacterial killing after anti-tuberculous chemotherapy compared to before. The simplicity of a whole blood culture facilitates its inclusion in a clinical trial and it may have a potential role as a surrogate marker in a TB vaccine trial.