Publications (13)69.21 Total impact
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Article: SATVI - after 10 years closing in on a new and better vaccine to prevent tuberculosis.
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ABSTRACT: The vision of the South African Tuberculosis Vaccine Initiative (SATVI) (www.satvi.uct.ac.za) is 'A World Without TB' and our mission is 'Innovative and high-quality TB vaccine research in Africa, to impact the global epidemic'. Over the last 10 years, our focus has been twofold: first, clinical trials of BCG and of new candidate vaccines, and second, complementary research that addresses critical questions in TB vaccine development. SATVI is now widely regarded as the leading TB vaccine clinical research site in the world.South African medical journal = Suid-Afrikaanse tydskrif vir geneeskunde 06/2012; 102(6):438-41. · 2.04 Impact Factor -
Article: Association of human TLR1 and TLR6 deficiency with altered immune responses to BCG vaccination in South African infants.
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ABSTRACT: The development of effective immunoprophylaxis against tuberculosis (TB) remains a global priority, but is hampered by a partially protective Bacillus Calmette-Guérin (BCG) vaccine and an incomplete understanding of the mechanisms of immunity to Mycobacterium tuberculosis. Although host genetic factors may be a primary reason for BCG's variable and inadequate efficacy, this possibility has not been intensively examined. We hypothesized that Toll-like receptor (TLR) variation is associated with altered in vivo immune responses to BCG. We examined whether functionally defined TLR pathway polymorphisms were associated with T cell cytokine responses in whole blood stimulated ex vivo with BCG 10 weeks after newborn BCG vaccination of South African infants. In the primary analysis, polymorphism TLR6_C745T (P249S) was associated with increased BCG-induced IFN-γ in both discovery (n = 240) and validation (n = 240) cohorts. In secondary analyses of the combined cohort, TLR1_T1805G (I602S) and TLR6_G1083C (synonymous) were associated with increased IFN-γ, TLR6_G1083C and TLR6_C745T were associated with increased IL-2, and TLR1_A1188T was associated with increased IFN-γ and IL-2. For each of these polymorphisms, the hypo-responsive allele, as defined by innate immunity signaling assays, was associated with increased production of TH1-type T cell cytokines (IFN-γ or IL-2). After stimulation with TLR1/6 lipopeptide ligands, PBMCs from TLR1/6-deficient individuals (stratified by TLR1_T1805G and TLR6_C745T hyporesponsive genotypes) secreted lower amounts of IL-6 and IL-10 compared to those with responsive TLR1/6 genotypes. In contrast, no IL-12p70 was secreted by PBMCs or monocytes. These data support a mechanism where TLR1/6 polymorphisms modulate TH1 T-cell polarization through genetic regulation of monocyte IL-10 secretion in the absence of IL-12. These studies provide evidence that functionally defined innate immune gene variants are associated with the development of adaptive immune responses after in vivo vaccination against a bacterial pathogen in humans. These findings could potentially guide novel adjuvant vaccine strategies as well as have implications for IFN-γ-based diagnostic testing for TB.PLoS Pathogens 08/2011; 7(8):e1002174. · 9.13 Impact Factor -
Article: Novel application of Ki67 to quantify antigen-specific in vitro lymphoproliferation.
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ABSTRACT: Antigen-specific proliferation is a critical function of memory T cells that is often utilised to measure vaccine immunogenicity and T cell function. We proposed that measurement of intracellular expression of the nuclear protein, Ki67, could reliably assess specific T cell proliferation in vitro. Ki67 was expressed in CD4+ and CD8+ T cells that had undergone in vitro proliferation after 6-day culture of human whole blood or PBMC with antigens. T cells cultured with no antigen did not express Ki67. When compared to current flow cytometry based proliferation assays, Ki67 detected proliferating cells with greater sensitivity than BrdU incorporation, whereas its sensitivity was similar to dye dilution of Oregon Green (OG), a CFSE derivative. Overall, the magnitude and cytokine expression profile of proliferating T cells detected by Ki67 expression correlated strongly with T cells detected with BrdU or OG. The intra-assay variability of Ki67 proliferation was 2-3% for CD4+ T cells, and 10-16% for CD8+ T cells. Finally, we demonstrate that the Ki67 assay detects tetanus toxoid-specific CD4+ T cell proliferation after infant vaccination with tetanus toxoid (TT). Overall our data suggest that intracellular Ki67 expression provides a specific, quantitative and reproducible measure of antigen-specific T cell proliferation in vitro.Journal of immunological methods 10/2010; 362(1-2):43-50. · 2.35 Impact Factor -
Article: Tuberculin skin test and in vitro assays provide complementary measures of antimycobacterial immunity in children and adolescents.
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ABSTRACT: Although many studies have compared in vitro TB diagnostic tests with the venerable tuberculin skin test (TST), there is little understanding of the quantitative relationship between critical measures of antimycobacterial immunity used to detect TB infection. We, therefore, decided to determine the degree of redundancy between quantitative read-outs of in vivo and in vitro assays of antimycobacterial immunity. We enrolled 475 healthy HIV-negative children and young adults living in a hyperendemic area of TB. We measured in vivo TST responses, and a 1:10 diluted 3- or 7-day whole-blood assay was used to determine the in vitro antigen-specific interferon (IFN)-gamma cytokine release. The frequency of antigen-specific IFN-gamma(+)CD4(+) and IFN-gamma(+)CD8(+) cells was tested using intracellular cytokine staining after 1 day incubation. In vivo TST responses segregated into two well-separated groups with either no measurable response (TST induration < 5 mm; n = 164) or a normally distributed group with TST indurations > or = 5 mm with peak at 15 mm (n = 260). In vitro assays provided a less pronounced separation of responders and nonresponders. Correlation analysis of responses among persons with TST > or = 5 mm demonstrated that extent of TST response was poorly correlated with IFN-gamma release (coefficients of correlation rho = 0.17-0.22) and frequency of IFN-gamma(+)CD4(+)/CD8(+) cells (rho = 0.05-0.17) across three stimulating antigens (Mycobacterium bovis bacillus Calmette-Guérin, purified protein derivative, early-secreted antigenic target-6). We conclude that in vivo and in vitro assays are nonredundant, complementary measures of antimycobacterial immunity. Both TST and in vitro assays provided valuable information about antimycobacterial immunity and by inference latent TB in the studied high-incidence TB settings.Chest 05/2010; 137(5):1071-7. · 5.25 Impact Factor -
Article: The novel tuberculosis vaccine, AERAS-402, induces robust and polyfunctional CD4+ and CD8+ T cells in adults.
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ABSTRACT: AERAS-402 is a novel tuberculosis vaccine designed to boost immunity primed by bacillus Calmette-Guérin (BCG), the only licensed vaccine. We investigated the safety and immunogenicity of AERAS-402 in healthy Mycobacterium tuberculosis-uninfected BCG-vaccinated adults from a tuberculosis-endemic region of South Africa. Escalating doses of AERAS-402 vaccine were administered intramuscularly to each of three groups of healthy South African BCG-vaccinated adults, and a fourth group received two injections of the maximal dose. Participants were monitored for 6 months, with all adverse effects documented. Vaccine-induced CD4(+) and CD8(+) T-cell immunity was characterized by an intracellular cytokine staining assay of whole blood and peripheral blood mononuclear cells. AERAS-402 was well tolerated, and no vaccine-related serious adverse events were recorded. The vaccine induced a robust CD4(+) T-cell response dominated by cells coexpressing IFN-gamma, tumor necrosis factor-alpha, and IL-2 ("polyfunctional" cells). AERAS-402 also induced a potent CD8(+) T-cell response, characterized by cells expressing IFN-gamma and/or tumor necrosis factor-alpha, which persisted for the duration of the study. Vaccination with AERAS-402 is safe and immunogenic in healthy adults. The immunity induced by the vaccine appears promising: polyfunctional T cells are thought to be important for protection against intracellular pathogens such as Mycobacterium tuberculosis, and evidence is accumulating that CD8(+) T cells are also important. AERAS-402 induced a robust and durable CD8(+) T-cell response, which appears extremely promising. Clinical trial registered with www.sanctr.gov.za (NHREC no. 1381).American Journal of Respiratory and Critical Care Medicine 02/2010; 181(12):1407-17. · 11.08 Impact Factor -
Article: High heritability of antimycobacterial immunity in an area of hyperendemicity for tuberculosis disease.
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ABSTRACT: Human antimycobacterial immunity is a critical component of tuberculosis (TB) pathogenesis that is often used to infer the presence of TB infection. We report high heritability (>50%) for in vitro secretion of tumor necrosis factor alpha and interferon gamma (IFN-gamma), and the frequency of antigen-specific IFN-gamma(+)CD4(+) and IFN-gamma(+)CD8(+) cells in the response of whole blood to mycobacterial challenge. In principal component analysis, the first 3 components explain 78% of the overall variance consistent with the effect of pleiotropic regulatory genes of human antimycobacterial immunity. These results directly demonstrate the pivotal role played by host genetics in quantitative measures of antimycobacterial immunity underlying immune diagnosis of TB infection.The Journal of Infectious Diseases 11/2009; 201(1):15-9. · 6.41 Impact Factor -
Article: Two loci control tuberculin skin test reactivity in an area hyperendemic for tuberculosis.
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ABSTRACT: Approximately 20% of persons living in areas hyperendemic for tuberculosis (TB) display persistent lack of tuberculin skin test (TST) reactivity and appear to be naturally resistant to infection by Mycobacterium tuberculosis. Among those with a positive response, the intensity of TST reactivity varies greatly. The genetic basis of TST reactivity is not known. We report on a genome-wide linkage search for loci that have an impact on TST reactivity, which is defined either as zero versus nonzero (TST-BINa) or as extent of TST in millimeters (TST-quantitative trait locus [QTL]) in a panel of 128 families, including 350 siblings, from an area of South Africa hyperendemic for TB. We detected a major locus (TST1) on chromosomal region 11p14 (P = 1.4 x 10(-5)), which controls TST-BINa, with a lack of responsiveness indicating T cell-independent resistance to M. tuberculosis. We also detected a second major locus (TST2) on chromosomal region 5p15 (P < 10(-5)), which controls TST-QTL or the intensity of T cell-mediated delayed type hypersensitivity (DTH) to tuberculin. Fine mapping of this region identified SLC6A3, encoding the dopamine transporter DAT1, as a promising gene for further studies. Our results pave the way for the understanding of the molecular mechanisms involved in resistance to M. tuberculosis infection in endemic areas (TST1) and for the identification of critical regulators of T cell-dependent DTH to tuberculin (TST2).Journal of Experimental Medicine 11/2009; 206(12):2583-91. · 13.85 Impact Factor -
Article: The potential impact of helminth infection on trials of novel tuberculosis vaccines.
Vaccine 06/2009; 27(35):4743-4. · 3.77 Impact Factor -
Article: Significantly skewed memory CD8+ T cell subsets in HIV-1 infected infants during the first year of life.
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ABSTRACT: HIV-1 infection causes a severe T cell compromise; however, little is known about changes in naive, memory, effector and senescent T cell subsets during the first year of life. T cell subsets were studied over the first year of life in blood from 3 infant cohorts: untreated HIV-infected, HIV-exposed but uninfected, and HIV-unexposed. In HIV-infected infants, the frequency of CCR7(+)CD45RA(+) naive CD8(+) T cells was significantly decreased, while the frequency of CCR7(-)CD45RA(-) effector memory CD8(+) T cells was increased, compared with the control cohorts. A larger population of CD8(+) T cells in HIV-infected infants displayed a phenotype consistent with senescence. Differences in CD4(+) T cell subset frequencies were less pronounced, and no significant differences were observed between exposed and unexposed HIV-uninfected infants. We concluded that the proportion of naive, memory, effector and senescent CD8(+) T cells during the first year of life is significantly altered by HIV-1 infection.Clinical Immunology 12/2008; 130(3):280-9. · 4.05 Impact Factor -
Article: A comparison of IFNgamma detection methods used in tuberculosis vaccine trials.
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ABSTRACT: Interferon gamma (IFNgamma) is a critical component of the pro-inflammatory immune response that provides protection against Mycobacterium tuberculosis. In the absence of an immunological correlate of protection, antigen-specific production of IFNgamma is a commonly used marker of a protective immune response. To facilitate the evaluation of tuberculosis candidate vaccines three different IFNgamma detection methods were compared. The cultured whole blood ELISA, ex vivo IFNgamma ELISpot and whole blood ex vivo intracellular cytokine staining (ICS) assays were performed head-to-head during a Phase I clinical trial using the candidate vaccine MVA85A. Whilst all three assays detected significant increases in IFNgamma production immediately following vaccination, distinctions between the assays were apparent. Higher baseline IFNgamma responses were detected using the cultured whole blood ELISA, whereas the ex vivo ELISpot assay was the most sensitive in detecting long-term (52 weeks) post-vaccination responses. The whole blood ex vivo ICS assay provided novel information by dissecting the IFNgamma response into responding CD4, CD8 and gamma/delta T cell subsets. Future tuberculosis vaccine trials and immunology studies should ideally include a combination of ex vivo and cultured assays to ensure a thorough and multifaceted evaluation of the immune response is achieved.Tuberculosis (Edinburgh, Scotland) 10/2008; 88(6):631-40. · 2.54 Impact Factor -
Article: CD8+ T-cell interleukin-7 receptor alpha expression as a potential indicator of disease status in HIV-infected children.
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ABSTRACT: Initiation and modification of antiretroviral therapy in HIV-infected children depend on viral load and CD4+ T-cell count. However, these surrogates have limitations, and complementary immunological markers to assess therapeutic response are needed. Our aim was to evaluate CD8+ T-cell expression of CD127 as a marker of disease status in HIV-infected children, based on adult data suggesting its usefulness. We hypothesized that CD127 expression on CD8+ T-cells is lower in children with more advanced disease. In a cross-sectional evaluation, we used flow cytometry to measure CD127+ expression on CD8+ T-cells in whole blood from HIV-infected children with varying disease status. This was compared with expression of CD38 on this subset, currently used in clinical practice as a marker of disease status. 51 HIV-infected children were enrolled. There was a strong positive correlation between CD127 expression on CD8+ T-cells and CD4+ T-cell count, and height and weight z-scores, and a strong negative correlation between CD127 expression and viral load. In contrast, we found no association between CD38 expression and these disease status markers. CD8+ T-cell CD127 expression is significantly higher in children with better HIV disease control, and may have a role as an immunologic indicator of disease status. Longitudinal studies are needed to determine the utility of this marker as a potential indicator of HIV disease progression.PLoS ONE 02/2008; 3(12):e3986. · 4.09 Impact Factor -
Article: Novel application of a whole blood intracellular cytokine detection assay to quantitate specific T-cell frequency in field studies.
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ABSTRACT: We optimized a whole blood intracellular cytokine assay to quantitate the frequency of specific CD4+ and CD8+ T cells in small volumes of whole blood from infants from developing countries. The assay is performed in two steps. First, whole blood is stimulated in the presence of specific antigens for 6-18 h, ending with cryopreservation of fixed white cells. These stimulation steps were specifically adapted to be practical and reliable in a rural, developing country field setting. Later, in a more resourceful setting, interferon-gamma producing CD4+ or CD8+ T cells are detected by flow cytometry. The assay proved sensitive and specific for detecting mycobacteria-specific immunity 10 weeks after Bacillus Calmette-Guerin (BCG) vaccination of newborns from a rural field site.Journal of Immunological Methods 09/2004; 291(1-2):185-95. · 2.20 Impact Factor -
Article: Serum immunoglobulin E levels in human immunodeficiency virus-infected children with pneumonia.
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ABSTRACT: Elevated serum immunoglobulin E (IgE) levels have been reported in association with human immunodeficiency virus (HIV) infection in adults, but there is little information in children. The aim of the present study was to compare serum IgE levels in HIV-positive and -negative children hospitalized with pneumonia in South Africa and to investigate whether IgE may be useful as a marker of specific infections or prognosis in HIV-infected children. History, examination, blood tests, and induced sputum or bronchoalveolar lavage were carried out. Of 122 children [45% female, median age 8 months (3-20 months)], 81 were infected with HIV. A history of allergy or asthma was present in three children (two of whom were HIV positive). Serum IgE was higher in HIV-infected children [83 (33-147) vs. 29 (6-113) IU/l; p = 0.011] as was immunoglobulin G (IgG) [49 (37-63) vs. 27.5 (23-34) g/l; p < 0.001]. CD4 lymphocytes [600 (330-1,210) vs. 1,900 (1,500-3,030) cells/ micro l], percentage CD4 cells [13.6 (9.4-20.3) vs. 40.1 (31.1-44.9)] and CD4 : CD8 ratio [0.3 (0.2-0.4) vs. 2 (1.4-2.8)] were lower in HIV-positive children (p < 0.001 for all). Bacteremia occurred in 12 (10%) children; other specific pathogens identified included Mycobacterium tuberculosis in eight (7%) and Pneumocystis carinii in nine (7%). There was no correlation with CD4 count, CD4 : CD8 ratio, or the presence of specific pathogens, and IgE level. In-hospital mortality (11%) did not correlate with IgE levels. HIV-infected children with pneumonia have higher serum IgE compared with seronegative patients. In HIV-positive children, IgE levels did not correlate with the degree of immunosuppression or with outcome.Pediatric Allergy and Immunology 10/2002; 13(5):328-33. · 2.46 Impact Factor
Top co-authors
Top Journals
Institutions
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2008–2010
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University of Cape Town
- • South African Tuberculosis Vaccine Initiative (SATVI)
- • Department of Child and Adolescent Health
Cape Town, Province of the Western Cape, South Africa -
Boston Children's Hospital
Boston, MA, USA
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