A New Vaccine for Tuberculosis: The Challenges of Development and Deployment

Structural analysis of mycobacterial homoserine transacetylases central to methionine biosynthesis reveals druggable active site

Mycobacterium tuberculosis is the cause of the world’s most deadly infectious disease. Efforts are underway to target the methionine biosynthesis pathway, as it is not part of the host metabolism. The homoserine transacetylase MetX converts l-homoserine to O-acetyl-l-homoserine at the committed step of this pathway. In order to facilitate structure-based drug design, we determined the high-resolution crystal structures of three MetX proteins, including M. tuberculosis (MtMetX), Mycolicibacterium abscessus (MaMetX), and Mycolicibacterium hassiacum (MhMetX). A comparison of homoserine transacetylases from other bacterial and fungal species reveals a high degree of structural conservation amongst the enzymes. Utilizing homologous structures with bound cofactors, we analyzed the potential ligandability of MetX. The deep active-site tunnel surrounding the catalytic serine yielded many consensus clusters during mapping, suggesting that MtMetX is highly druggable.

Enhancement of immune response against Mycobacterium tuberculosis HspX antigen by incorporation of combined molecular adjuvant (CASAC)

Tuberculosis (TB) is one of the deadliest human diseases worldwide caused by mycobacterial infection in the lung. Bacillus Calmette-Guerin (BCG) vaccine protects against disseminated TB in children, but its effectiveness is still questionable due to highly variable protections in adolescence and elderly individuals. Targeting the latency M.tb antigen is a recent therapeutic approach to eradicate dormant pathogen that could possibly lead to disease activation. In this study, we aimed to potentiate immune responses elicited against 16 kDa α-crystalline (HspX) tuberculosis latency antigen by incorporation of Combined Adjuvant for Synergistic Activation of Cellular immunity (CASAC). Histidine-tagged recombinant HspX protein was initially produced in Escherichia coli and purified using Ni-NTA chromatography. To evaluate its adjuvanticity, C57BL/6 mice (n = 5) were initially primed and intradermally immunised in 2-weeks interval for 4 rounds with recombinant HspX, formulated with and without CASAC. Humoral and cell-mediated immune responses elicited against HspX antigen were evaluated using ELISA and Flow Cytometry. Our findings showed that CASAC improved humoral immunity with increased antigen-specific IgG1 and IgG2a antibody response. Stronger CD8+ and Th1-driven immunity was induced by CASAC formulation as supported by elevated level of IFN-γ, TNF-α, IL-12 and IL-17A; and with low IL-10 secretion. Interestingly, adjuvanted HspX vaccine triggered a higher percentage of effector memory T-cell population than those immunised with unadjuvanted vaccine. In conclusion, CASAC adjuvant has great potential to enhance immunogenicity elicited against HspX antigen, which could be an alternative regimen to improve the efficacy of future therapeutic vaccine against Mycobacterium tuberculosis.

Where Caring Is Sharing: Evolving Ethical Considerations in Tuberculosis Prevention Among Healthcare Workers

In many settings, the dedication of healthcare workers (HCWs) to the treatment of tuberculosis exposes them to serious risks. Current ethical considerations related to tuberculosis prevention in HCWs involve the threat posed by comorbidities, issues of power and space, the implications of intersectoral collaborations, (de)professionalization, just remuneration, the duty to care, and involvement in research. Emerging ethical considerations include mandatory vaccination and the use of geolocalization services and information technologies. The following exploration of these various ethical considerations demonstrates that the language of ethics can fruitfully be deployed to shed new light on policies that have repercussions on the lives of HCWs in underresourced settings. The language of ethics can help responsible parties get a clearer sense of what they owe HCWs, particularly when these individuals are poorly compensated, and it shows that it is essential that HCWs' contribution be acknowledged through a shared commitment to alleviate ethically problematic aspects of the environments within which they provide care. For this reason, there is a strong case for the community of bioethicists to continue to take greater interest both in the micro-level (eg, patient-provider interactions) and macro-level (eg, injustices that occur as a result of the world order) issues that put HCWs working in areas with high tuberculosis prevalence in ethically untenable positions. Ultimately, appropriate responses to the various ethical considerations explored here must vary based on the setting, but, as this article shows, they require thoughtful reflection and courageous action on the part of governments, policy makers, and managers responsible for national responses to the tuberculosis epidemic.

Diagnostic features associated with culture of Mycobacterium tuberculosis among young children in a vaccine trial setting

OBJECTIVES

To identify diagnostic features associated with culture of Mycobacterium tuberculosis (MTB), the standard for tuberculosis (TB) diagnosis, to inform clinical end point definitions for new TB vaccine trials.

METHODS

Children <2 years of age (n = 1445) were screened and investigated for TB during a Bacille Calmette Guerin vaccine trial in South Africa. Standardized clinical, radiologic, and microbiologic data were collected, including paired gastric lavage and induced sputum for MTB liquid culture. Adjusted odds ratios (AORs) were calculated using a multivariate logistic regression model.

RESULTS

Adjusted odds of positive MTB culture increased by 90% with history of wheezing (AOR, 1.9) and by 4% with each 1-mm increase in Mantoux diameter (AOR, 1.04). Odds of positive MTB culture doubled if the chest radiograph was suggestive of pulmonary TB (AOR, 2.16) and more than tripled if lower chest retraction was observed clinically (AOR, 3.37). Fever, night sweats, and presence of lymphadenopathy were negatively associated with MTB culture (AOR: 0.5, 0.62, and 0.2, respectively). Persistent cough, weight loss, and failure to thrive were not significantly associated with MTB culture in this study population.

CONCLUSIONS

Wheezing and lower chest retraction, consistent with intrathoracic airway obstruction; chest radiography suggestive of pulmonary tuberculosis; and Mantoux diameter were predictive of positive MTB culture. These variables should be considered for inclusion in composite clinical end point definitions for infant TB vaccine trials. Several clinical features, commonly used for TB diagnosis in older children, were not associated with positive MTB culture among children younger than 2 years.

Cost-effectiveness of novel vaccines for tuberculosis control: a decision analysis study

BACKGROUND

The development of a successful new tuberculosis (TB) vaccine would circumvent many limitations of current diagnostic and treatment practices. However, vaccine development is complex and costly. We aimed to assess the potential cost effectiveness of novel vaccines for TB control in a sub-Saharan African country--Zambia--relative to the existing strategy of directly observed treatment, short course (DOTS) and current level of bacille Calmette-Guérin (BCG) vaccination coverage.

METHODS

We conducted a decision analysis model-based simulation from the societal perspective, with a 3% discount rate and all costs expressed in 2007 US dollars. Health outcomes and costs were projected over a 30-year period, for persons born in Zambia (population 11,478,000 in 2005) in year 1. Initial development costs for single vaccination and prime-boost strategies were prorated to the Zambian share (0.398%) of global BCG vaccine coverage for newborns. Main outcome measures were TB-related morbidity, mortality, and costs over a range of potential scenarios for vaccine efficacy.

RESULTS

Relative to the status quo strategy, a BCG replacement vaccine administered at birth, with 70% efficacy in preventing rapid progression to TB disease after initial infection, is estimated to avert 932 TB cases and 422 TB-related deaths (prevention of 199 cases/100,000 vaccinated, and 90 deaths/100,000 vaccinated). This would result in estimated net savings of $3.6 million over 30 years for 468,073 Zambians born in year 1 of the simulation. The addition of a booster at age 10 results in estimated savings of $5.6 million compared to the status quo, averting 1,863 TB cases and 1,011 TB-related deaths (prevention of 398 cases/100,000 vaccinated, and of 216 deaths/100,000 vaccinated). With vaccination at birth alone, net savings would be realized within 1 year, whereas the prime-boost strategy would require an additional 5 years to realize savings, reflecting a greater initial development cost.

CONCLUSIONS

Investment in an improved TB vaccine is predicted to result in considerable cost savings, as well as a reduction in TB morbidity and TB-related mortality, when added to existing control strategies. For a vaccine with waning efficacy, a prime-boost strategy is more cost-effective in the long term.

Bridging the gap: improving clinical development and the regulatory pathways for health products for neglected diseases

Background There has been tremendous progress over the last decade in the development of health products — drugs, vaccines, and diagnostics — for neglected diseases. There are now dozens of candidate products in the pipeline.

Purpose Our purpose is to assess challenges that will arise in later-stage clinical development of these candidate health products and propose a strategy that would help bring the costs, risks, and finances for their clinical trials into a better, more sustainable balance.

Methods We conducted a literature review of clinical trial-related publications, interviewed individuals sponsoring and conducting interventional clinical trials for neglected diseases, and analyzed data from Clinicaltrials.gov, a clinical trials registry, on neglected disease clinical trials initiating subject recruitment between January 1, 2003 and December 31, 2009. We quantified Clinicaltrials.gov data into country-specific participation in clinical trials and aggregated them into geographic regions. We employed bioinformatics and keyword methods to classify trials by type of intervention, sponsor, study phase, and therapeutic area.

Results Two substantial bottlenecks threaten our capacity to bring these candidate neglected disease therapies to those in need. First, the research and regulatory capacity in many neglected disease-endemic settings is not adequate to support the clinical trials that need to occur there in order to complete the development of these products. Second, even with expected attrition in the pipeline, current levels of financing are insufficient to support the clinical development of these products under current cost assumptions.

Limitations The proportion of trials of relevant studies not registered on Clinicaltrials.gov is not known, but is thought to be smaller post-2005, after the International Committee of Medical Journal Editors initiated a policy requiring investigators to deposit information about trial design into an accepted clinical trials registry before beginning patient enrollment.

Conclusions Realizing the promise of the neglected disease product pipeline will require not only increased funding for large-scale clinical trials and capacity building, but also greater attention to how these trials and their regulatory pathways can be improved to reduce unnecessary costs, delays, and risks to trial subjects. We propose a two-prong strategy: (1) adaptation and adoption of emerging research on ‘sensible guidelines’ for reducing large-scale, randomized clinical trial costs to the demands of the neglected disease product pipeline and (2) regional approaches to regulation and ethical review of clinical trials for health products for neglected diseases.