Sizulu Moyo

Modified vaccinia Ankara-expressing Ag85A, a novel tuberculosis vaccine, is safe in adolescents and children, and induces polyfunctional CD4+ T cells

Modified vaccinia Ankara‐expressing Ag85A (MVA85A) is a new tuberculosis (TB) vaccine aimed at enhancing immunity induced by BCG. We investigated the safety and immunogenicity of MVA85A in healthy adolescents and children from a TB endemic region, who received BCG at birth. Twelve adolescents and 24 children were vaccinated and followed up for 12 or 6 months, respectively. Adverse events were documented and vaccine‐induced immune responses assessed by IFN‐γ ELISpot and intracellular cytokine staining. The vaccine was well tolerated and there were no vaccine‐related serious adverse events. MVA85A induced potent and durable T‐cell responses. Multiple CD4+ T‐cell subsets, based on expression of IFN‐γ, TNF‐α, IL‐2, IL‐17 and GM‐CSF, were induced. Polyfunctional CD4+ T cells co‐expressing IFN‐γ, TNF‐α and IL‐2 dominated the response in both age groups. A novel CD4+ cell subset co‐expressing these three Th1 cytokines and IL‐17 was induced in adolescents, while a novel CD4+ T‐cell subset co‐expressing Th1 cytokines and GM‐CSF was induced in children. Ag‐specific CD8+ T cells were not detected. We conclude that in adolescents and children MVA85A safely induces the type of immunity thought to be important in protection against TB. This includes induction of novel Th1‐cell populations that have not been previously described in humans.

The utility of an interferon gamma release assay for diagnosis of latent tuberculosis infection and disease in children: a systematic review and meta-analysis.

Background: The utility of interferon gamma release assays (IGRAs) has been assessed in adults, but remains unclear in children. We reviewed the literature on the use of a commercial IGRA in immunocompetent children for the diagnosis of both latent tuberculosis infection (LTBI) and TB disease. Methods: We searched PubMed for studies published before January 2010 on the diagnosis of TB in children using an IGRA. We compared the specificity and sensitivity of the tuberculin skin test (TST) and the IGRA for LTBI and conducted a random effects meta-analysis on sensitivity of the IGRA for TB disease. Results: Of 68 studies identified, 20 were included in this review. There was increased specificity of the IGRA for LTBI in children compared with TST, but varying sensitivities. Sensitivity of the IGRA in detecting TB disease in children also varied when compared with TST (mean &kgr; score, 0.57). For all TB cases, the pooled sensitivity was 66% (95% confidence interval [CI], 53%–78%) with heterogeneity (I2 = 74.8%). Stratification by background TB incidence highlighted a significantly reduced IGRA sensitivity of 55% (95% CI, 37%–73%) in high incidence settings when compared with low incidence settings, 70% (95% CI, 53%–84%). Conclusions: There was no clear evidence that IGRAs should replace TST for detecting LTBI in children. Sensitivity of the IGRA for TB disease was no different from TST, and a significantly reduced IGRA sensitivity was found in high-burden TB settings compared with low-burden TB settings. Further studies are needed to determine the value of IGRAs in LTBI and TB disease diagnosis in children.

A Phase IIa Trial of the New Tuberculosis Vaccine, MVA85A, in HIV- and/or Mycobacterium tuberculosis–infected Adults

RATIONALE Novel tuberculosis (TB) vaccines should be safe and effective in populations infected with Mycobacterium tuberculosis (M.tb) and/or HIV for effective TB control. OBJECTIVE To determine the safety and immunogenicity of MVA85A, a novel TB vaccine, among M.tb- and/or HIV-infected persons in a setting where TB and HIV are endemic. METHODS An open-label, phase IIa trial was conducted in 48 adults with M.tb and/or HIV infection. Safety and immunogenicity were analyzed up to 52 weeks after intradermal vaccination with 5 × 10(7) plaque-forming units of MVA85A. Specific T-cell responses were characterized by IFN-γ enzyme-linked immunospot and whole blood intracellular cytokine staining assays. MEASUREMENTS AND MAIN RESULTS MVA85A was well tolerated and no vaccine-related serious adverse events were recorded. MVA85A induced robust and durable response of mostly polyfunctional CD4(+) T cells, coexpressing IFN-γ, tumor necrosis factor-α, and IL-2. Magnitudes of pre- and postvaccination T-cell responses were lower in HIV-infected, compared with HIV-uninfected, vaccinees. No significant effect of antiretroviral therapy on immunogenicity of MVA85A was observed. CONCLUSIONS MVA85A was safe and immunogenic in persons with HIV and/or M.tb infection. These results support further evaluation of safety and efficacy of this vaccine for prevention of TB in these target populations.

Dose-Finding Study of the Novel Tuberculosis Vaccine, MVA85A, in Healthy BCG-Vaccinated Infants

BACKGROUND BCG, the only licensed tuberculosis vaccine, affords poor protection against lung tuberculosis in infants and children. A new tuberculosis vaccine, which may enhance the BCG-induced immune response, is urgently needed. We assessed the safety of and characterized the T cell response induced by 3 doses of the candidate vaccine, MVA85A, in BCG-vaccinated infants from a setting where tuberculosis is endemic. METHODS  Infants aged 5-12 months were vaccinated intradermally with either 2.5 × 10(7), 5 × 10(7), or 10 × 10(7) plaque-forming units of MVA85A, or placebo. Adverse events were documented, and T-cell responses were assessed by interferon γ (IFN-γ) enzyme-linked immunospot assay and intracellular cytokine staining. RESULTS The 3 MVA85A doses were well tolerated, and no vaccine-related serious adverse events were recorded. MVA85A induced potent, durable T-cell responses, which exceeded prevaccination responses up to 168 d after vaccination. No dose-related differences in response magnitude were observed. Multiple CD4 T cell subsets were induced; polyfunctional CD4 T cells co-expressing T-helper cell 1 cytokines with or without granulocyte-macrophage colony-stimulating factor predominated. IFN-γ-expressing CD8 T cells, which peaked later than CD4 T cells, were also detectable. CONCLUSIONS MVA85A was safe and induced robust, polyfunctional, durable CD4 and CD8 T-cell responses in infants. These data support efficacy evaluation of MVA85A to prevent tuberculosis in infancy. Clinical Trials Registration. NCT00679159.

Structured approaches for the screening and diagnosis of childhood tuberculosis in a high prevalence region of South Africa

OBJECTIVE To measure agreement between nine structured approaches for diagnosing childhood tuberculosis; to quantify differences in the number of tuberculosis cases diagnosed with the different approaches, and to determine the distribution of cases in different categories of diagnostic certainty. METHODS We investigated 1445 children aged < 2 years during a vaccine trial (2001-2006) in a rural South African community. Clinical, radiological and microbiological data were collected prospectively. Tuberculosis case status was determined using each of the nine diagnostic approaches. We calculated differences in case frequency and categorical agreement for binary (tuberculosis/not tuberculosis) outcomes using McNemars test (with 95% confidence intervals, CIs) and Cohens kappa coefficient (Kappa). FINDINGS Tuberculosis case frequency ranged from 6.9% to 89.2% (median: 41.7). Significant differences in case frequency (P < 0.05) occurred in 34 of the 36 pair-wise comparisons between structured diagnostic approaches (range of absolute differences: 1.5-82.3%). Kappa ranged from 0.02 to 0.71 (median: 0.18). The two systems that yielded the highest case frequencies (89.2% and 70.0%) showed fair agreement (Kappa: 0.33); the two that yielded the lowest case frequencies (6.9% and 10.0%) showed slight agreement (Kappa: 0.18). CONCLUSION There is only slight agreement between structured approaches for the screening and diagnosis of childhood tuberculosis and high variability between them in terms of case yield. Diagnostic systems that yield similarly low case frequencies may be identifying different subpopulations of children. The study findings do not support the routine clinical use of structured approaches for the definitive diagnosis of childhood tuberculosis, although high-yielding systems may be useful screening tools.

Tuberculin skin test and QuantiFERON® assay in young children investigated for tuberculosis in South Africa.

SETTING Although the literature on interferon-gamma release assays on tuberculosis (TB) in children has increased, data pertaining to young children remain relatively limited. OBJECTIVE To compare results from the tuberculin skin test (TST) and the QuantiFERON®-TB Gold In-Tube assay (QFT) in children aged <3 years investigated for TB disease. DESIGN TB suspects were evaluated by medical history and examination, TST, QFT, chest radiography, induced sputum and gastric washings for smear and culture for Mycobacterium tuberculosis. RESULTS A total of 400 children were enrolled. Among 397 children with both test results, 68 (17%) were QFT-positive and 72 (18%) were TST-positive (≥10 mm). Agreement between the tests was excellent (94%, κ = 0.79, 95%CI 0.69-0.89). TB disease was diagnosed in 52/397 (13%) participants: 3 definite, 35 probable and 14 possible TB. QFT sensitivity and specificity for TB disease were respectively 38% and 81%. TST sensitivity and specificity were respectively 35% and 84%. CONCLUSION While TST and QFT had excellent concordance in this population, both tests had much lower sensitivity for TB disease than has been reported for other age groups. Our results suggested equivalent performance of QFT and TST in the diagnosis of TB disease in young children in a high-burden setting.

Tuberculosis case finding for vaccine trials in young children in high-incidence settings: a randomised trial

SETTING A high tuberculosis (TB) burden rural area in South Africa. OBJECTIVE To compare TB case yield and disease profile among bacille Calmette-Guérin (BCG) vaccinated children using two case-finding strategies from birth until 2 years of age. DESIGN BCG-vaccinated infants were enrolled within 2 weeks of birth and randomised to 3-monthly home visits for questionnaire-based TB screening plus record surveillance of TB registers, hospital admission and X-ray lists at health facilities for TB suspects and cases (Group 1), or record surveillance (as above) only (Group 2). Both groups received a close-out visit after 2 years. Participants were evaluated for suspected TB disease using standardised investigations. RESULTS A total of 4786 infants were enrolled: 2392 were randomised to Group 1 and 2394 to Group 2. The case-finding rate was significantly greater in Group 1 (2.2/100 py) than in Group 2 (0.8/100 py), with a case-finding rate ratio of 2.6 (95%CI 1.8-4.0, P < 0.001). Although the proportion of cases with bacteriological confirmation was lower in Group 1, this difference did not reach statistical significance. There was also no significant difference in the proportions with TB symptoms and signs. CONCLUSION Home visits combined with record surveillance detected significantly more cases than record surveillance with a single study-end visit. The TB case profile did not differ significantly between the two groups.

Phenotypic variability in childhood TB: implications for diagnostic endpoints in tuberculosis vaccine trials.

The endpoint definition for infant tuberculosis (TB) vaccine trials should match the TB disease phenotype expected in the control arm of the study population. Our aim was to analyse selected combinations of the clinical, radiological, and microbiological features of pulmonary TB among children investigated under vaccine trial conditions, in order to estimate case frequency for a range of expected TB phenotypes. Two thousand one hundred and eighty five South African children were investigated over a nine-year period (2001-2009). Evidence of TB exposure and classical symptoms were several times more common than chest radiography (CXR) compatible with TB, or positive Mycobacterium tuberculosis culture. Discordance between clinical, radiological, and microbiological features was common in individual children. Up to one third of children with compatible CXR, and up to half the children who were M. tuberculosis culture positive, were asymptomatic. The culture positive rate fell over time, although rates of TB exposure and compatible chest radiography increased. Consequently, the annual incidence of diagnostic combinations that included M. tuberculosis culture fell to <0.2%. However, in this study population (children <2 years of age), annual incidence of the TB disease phenotype that included the triad of TB exposure, symptoms, and compatible CXR, approached 1% (n=848 per 100,000). These findings allow modelling of expected TB case frequency in multi-centre infant TB vaccine trials, based upon benchmarking of diagnostic data against the key indicator variables that constitute the building blocks of a trial endpoint.

Time to Symptom Resolution in Young Children Treated for Pulmonary Tuberculosis

Background: Response to treatment may be useful for diagnostic confirmation of childhood tuberculosis (TB). We aimed to evaluate time to symptom resolution in children treated for pulmonary TB. Methods: We compared pulmonary TB cases and noncases, classified by a published diagnostic algorithm, in South African children younger than 2. TB treatment was prescribed independently on clinical grounds. We analyzed independent determinants of baseline symptom resolution by Cox regression. Results: One hundred and ninety-one symptomatic children, median age 12 months, were prescribed for TB treatment. Chest radiograph features of TB were associated with longer time to resolution of cough (adjusted hazard ratio, AHR 0.31), wheeze (AHR 0.26) and failure to thrive (AHR 0.41), (all P < 0.05). However, median duration of baseline cough (63 vs. 70 days, P = 0.98), wheeze (62 vs. 68 days, P = 0.87) and failure to thrive (76 vs. 66 days, P = 0.59) did not differ in TB cases (n = 48) versus noncases (n = 46). Conclusions: Baseline symptoms take more than 60 days to resolve in the majority of young children after starting TB treatment. Furthermore, since time to resolution does not differentiate TB cases from noncases; clinical response to treatment is not an appropriate diagnostic criterion for pediatric trials of TB diagnostics, drugs and vaccines.

Determining causes of mortality in children enrolled in a vaccine field trial in a rural area in the Western Cape Province of South Africa.

Aim:  A mortality surveillance system was developed to identify and document causes of death among children enrolled in a tuberculosis vaccine field trial in South Africa. The aims of this study were to describe causes of mortality in children enrolled in a phase IV trial comparing intradermal with percutaneous administration of Bacille Calmette Guerin, and to compare causes of mortality recorded on death certificates with those obtained by clinical record review combined with verbal autopsies (CR/VA).