ProfessorRobertWilkinson

Summary

Understanding and intervening in HIV-1 associated tuberculosis 

Introduction

HIV and TB are amongst the most pressing public health problems in Africa. The epidemiology of HIV associated TB is well researched, but few studies have addressed in detail the mechanisms. This programme aims to answer questions arising from the clinical care of patients with these infections. Over time the emphasis has increasingly encompassed the need for novel interventions. Projects underway at present include the following. 

• How can tuberculosis infection in HIV infected people be more effectively diagnosed and prevented? 

• By what immune mechanism does vitamin D decrease susceptibility to TB? 

• What is the cause and best management of the HIV-Tuberculosis-associated Immune Reconstitution Inflammatory Syndrome? 

• What is the pathogenesis of tuberculous pericarditis? 

• What is the Biology of human latent tuberculosis and how is tthis alterned by HIV-1 co-infection?

Research in progress

Under the categories listed above

 • How can tuberculosis infection in HIV infected people be more effectively diagnosed and prevented? 

An HIV driven epidemic of tuberculosis is underway in Khayelitsha township where the annual risk of TB is around 1.5%, and much higher in persons with HIV-1 infection. The limited TB control measures presently available need urgently to be augmented. We have completed, presented and submitted a pragmatic clinical trial of isoniazid (IPT) plus antiretroviral (ART) therapy to prevent tuberculosis. 1,329 participants contributed 3,227 person-years (PY) of follow up in the modified intention-to-treat analysis; 662 on placebo and 667 on IPT. There were 95 incident tuberculosis cases: 2.3 (95%CI 1.6-3.1) versus 3.6 (95%CI 2.8-4.7) per 100 PY in the IPT and placebo arms respectively (hazard ratio 0.63, 95%CI 0.41-0.94). Study drug was discontinued due to Grade 3 or 4 raised liver tansaminases in 2.9% and 1.3% in the IPT and placebo arms respectively (Risk Ratio=2.13, 95%CI 0.97-4.67). In secondary analyses, there was no evidence that the effect of IPT was restricted to those who were tuberculin skin test (TST, P=0.6) or interferon gamma release assay (IGRA P=0.2) positive: adjusted hazard ratio for those with negative tests 0.43 (95%CI 0.21-0.86) and 0.43 (95%CI 0.20-0.96); for positive tests 0.86 (95%CI 0.37-2.00) and 0.55 (95%CI 0.26-1.24) respectively.  No all cause mortality benefit of IPT was demonstrated. These findings have already resulted in modified policy by WHO.  We previously published a highly cited review (Rangaka et al. Lancet Infect Dis, 2012) on Predictive value of interferon-γ release assays for incident active tuberculosis. We concluded neither IGRAs nor the TST have high accuracy for the prediction of active tuberculosis, although use of IGRAs in some populations might reduce the number of people considered for preventive treatment. These findings influenced WHO advice on the utility of IGRA in high incidence settings.  Recognising this limitation of IGRA testing, two separate studies have examined the hypothesis that tuberculosis may be associated with a distinct transcriptomic signature in whole blood. The first of these conducted in collaboration with Dr Anne O’Garra at the MRC National Institute for Medical Research in London was published by Nature in 2010 and has been cited 209 times. We have followed up this study by tracking the response during the course of treatment. A change in signature was significantly detectable as early as 2 weeks providing potential early biomarkers for treatment monitoring.   The other project is a multicentre study that was administered by Brighton and Sussex Medical School and funded by the European Union (EU) and aimed to evaluate the diagnostic potential of biosignature. Samples were analysed in collaboration with the Genome Institute of Singapore and Imperial College. The study has confirmed a blood transcriptional signature that can distinguish TB from other conditions prevalent in Africa in HIV infected and uninfected patients. A new method for multi-transcript analysis suggests feasibility of a transcriptome based diagnostic test for TB in Africa. These findings are under consideration in a revised manuscript. A paper on the utility of such an approach in paediatric tuberculosis is also under review.  We completed randomization of 292 healthy HIV-1 infected persons to a Phase II, Proof of Concept, randomized, double-blind, placebo-controlled study to evaluate the protective efficacy against TB Disease, safety, and immunogenicity of the tuberculosis vaccine MVA85A. Thus we are now in follow-up phase on this multicenter collaboration that includes the University of Oxford, and Hopital Aristide Le Dantec in Senegal. Aeras is the sponsor. The trial has led to considerable development such that the clinical site is now ICH-GCP compliant, and has pharmacy and digital radiography facilities. There is a wired link to the University of Cape Town network. 

• By what immune mechanism does vitamin D decrease susceptibility to TB? 

Calcidiol, the major circulating metabolite of vitamin D, supports induction of pleiotropic antimicrobial and anti-inflammatory responses in vitro. In a subanalysis of a reported clinical trial we investigated, by means of longitudinal study, circulating and antigen-stimulated immune responses in ninety-five patients receiving antimicrobial therapy for pulmonary tuberculosis who were randomised to receive adjunctive high-dose vitamin D or placebo (Coussens et al. PNAS 2012). Vitamin D supplementation accelerated sputum smear conversion and enhanced treatment-induced resolution of lymphopaenia, monocytosis, hypercytokinaemia and hyperchemokinaemia. Administration of vitamin D also suppressed antigen-stimulated proinflammatory cytokine responses, but attenuated the suppressive effect of antimicrobial therapy on antigen-stimulated secretion of interleukin-4, CC chemokine ligand 5 and interferon-α. These findings findings suggest a potential role for adjunctive vitamin D supplementation in the treatment of pulmonary infections to accelerate resolution of inflammatory responses associated with increased risk of mortality. 

• What is the cause and best management of the HIV-Tuberculosis-associated Immune Reconstitution Inflammatory Syndrome? 

HIV-tuberculosis-associated immune reconstitution inflammatory syndrome (TB-IRIS) is an immunopathological reaction to mycobacterial antigens induced by antiretroviral therapy (ART). We are recognised world leaders in this field and co-convened a satelite symposium at the XIX AIDS 2012 conference in Washington DC. In the last year we have published findings on the role of the interleukin 10 family of cytokines in TB-IRIS finding that IL-10 and IL-22 were differentially induced in blood cells from tuberculosis-IRIS patients after in vitro stimulation, and higher concentrations of their corresponding proteins were detected in serum (in vivo). The higher levels of IL-10 observed in this study may represent a compensatory anti-inflammatory response during tuberculosis-IRIS. The elevated levels of IL-22 suggest an association between this cytokine and immunopathology during tuberculosis-IRIS.  Work on the frequency, severity, and prediction of tuberculous meningitis immune reconstitution inflammatory syndrome (TBM-IRIS) was also recently published. TBM-IRIS is a frequent, severe complication of antiretroviral therapy (ART) in HIV-associated TBM and is characterized by high cerebrospinal fluid (CSF) neutrophil counts and Mycobacterium tuberculosis culture positivity at TBM presentation. The combination of CSF IFN-γ and TNF-α concentrations may predict TBM-IRIS and thereby be a means to individualize patients to early or deferred ART. 

• What is the pathogenesis of tuberculous pericarditis? 

Effusive constrictive pericarditis is an uncommon pericardial syndrome in non-tuberculous pericardial disease. This syndrome is characterized by visceral constriction in the presence of compressive pericardial fluid and considered an indication for pericardiectomy. We have recently completed a prospective study to determine the prevalence, cytokine profile, and outcome of tuberculous effusive constrictive pericarditis. Compared to participants with non-constrictive effusive pericarditis, those with effusive constrictive disease had higher serum values of interleukin-10 and transforming growth factor-beta, and higher pericardial fluid values of IL-10 and interferon-gamma. This mixed inflammatory picture may set up chronic unresolving inflammation and fibrosis, and is a risk for constriction and mortality in one third of cases.   Further insight into this condition was provided by a study of N-acetyl-seryl-aspartyl-lysylproline (Ac-SDKP), a ubiquitous tetrapeptide with important antifibrotic properties, and galectin-3 which is an activator of myofibroblasts, promoter of collagen and extracellular matrix deposition associated with organ fibrosis. Ac-SDKP, which is inactivated by angiotensin converting enzyme, exerts part of its antifibrotic effect by inhibiting galectin-3. We showed that Ac-SDKP and galectin-3 are detectable in normal pericardial fluid, and that tuberculous pericarditis is associated with low levels of pericardial Ac-SDKP and normal galectin-3 levels. These observations pertaining to the levels of Ac-SDKP and galectin-3 in normal pericardial fluid and tuberculous pericardial effusion suggest that Ac-SDKP and galectin-3 play a housekeeping function within the normal pericardium similar to that in ventricles and kidneys. Furthermore, our results raise the possibility that both molecules play an important role maintaining the health of the pericardium during times of physiological or pathological stress. The depressed levels of Ac-SDKP in conjunction with normal or low levels of galectin-3 within the pericardium may provide a novel explanation for the high incidence of constrictive pericarditis associated with tuberculous pericarditis 

• What is the Biology of human latent tuberculosis?

Treatment of latent tuberculosis (LTBI) is a vital component of tuberculosis elimination but is not efficiently implemented with available diagnostics and therapeutics. In pursuit of a hypothesis that this condition is heterogeneous we have performed FDG-PET/CT scans on 35 asymptomatic HIV-1 infected, antiretroviral naïve persons with a median CD4 517/mm³, no previous history of active TB and positive Quantiferon Gold in tube (QFGIT) (but not recent contacts) ie clinically latent TB. 2/35 were culture positive despite being symptom free (subclinical TB).  75% of participants had abnormalities consistent with TB within the lungs with lesions falling in to 2 distinct patterns.  Sub-centimeter nodules equally distributed between lung lobes mainly sub-pleurally, 23% of which are mineralized and 6% showing increase FDG uptake, consistent with autopsy studies these are likely to represent sites of primary infection[15].  23% had infiltrates or fibrotic scars exclusively within the upper lobes of the lungs of which 29% have evidence disease activity on both CT and PET, again consist with autopsy studies and are likely to represent sites of reactivation at different stages of progression and healing.  Mediastinal and hilar lymph nodes showed abnormal FDG uptake in 50% however which may be TB or HIV-1 related, and which can only be inferred post TB treatment.

 

Right: Collaborating with Medecins Sans Frontieres-South Africa and the provincial and City Health authorities, we have our major community site in Khayelitsha site B where the incidence of tuberculosis is 1614/100000 with 67% cases being HIV associated.

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