Development of novel T cell assays and assessment of immune recognition to latency associated M.tuberculosis-specific antigens Rv2660 and Rv2659

Master Thesis


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University of Cape Town

Nearly 130 years have elapsed since the discovery of Mycobacterium tuberculosis (M.tb), the causative agent of tuberculosis, yet today it is estimated that 1 in every 3 of the worldʼs population is infected with this pathogen. In South Africa alone there were approximately 1000 new TB cases per 100 000 population in 2007, ranking the country second in incidence rate, globally. Hence research into new vaccine strategies to control the epidemic is vital. Current vaccines under development are prophylactic and designed to boost pre-existing immunity induced by the only licensed TB vaccine, BCG. A new approach is the development of a post-infection vaccine aimed at inducing an immune response that prevents progression to TB disease when administered to individuals latently infected with M.tb. This vaccine would have a dramatic impact on the worldwide TB burden. Our objective was to address 2 areas in TB vaccinology, firstly a novel postinfection TB vaccine strategy, and secondly, optimal measurement of vaccineinduced responses using a new immunological assay. The aim of the first study was to investigate human T cell responses to antigens that have been associated with M.tb latency. Rv2660 and Rv2659 were investigated, as these antigens are candidate antigens for a postinfection vaccine based on findings from in vitro models of M.tb suggesting preferential expression during latency in vivo. No information exists on the immune response to these antigens in M.tb infected or TB diseased individuals. Hence, we investigated the immune recognition of Rv2660 and Rv2659 in these 2 groups, and further characterised the nature of these antigen-specific T cell responses. We observed that (i) these antigens are significantly more likely to be recognised during M.tb infection compared with TB disease as shown by measurement of soluble IFN-γ in response to the specific antigens, (ii) M.tb infected persons had greater Rv2660- and Rv2659- specific CD4+ T cell proliferation and associated cytokine expression compared, with TB diseased persons. We propose that Rv2660 and Rv2659 may be candidates for incorporation into a post-infection vaccine.

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Includes bibliographical references (leaves 93-109).