Tuberculosis causes 2-3 million deaths each year. A more effective vaccine than BCG is required, but rational vaccine trials cannot be planned for two main reasons. Firstly, although many mycobacterial antigens have been isolated, it is not known which ones to test in human trials and it is not possible to test them all. Secondly, it is not known which mechanisms are crucial for killing M. tuberculosis in man, so an adjuvant cannot rationally be selected or short term pilot studies planned using surrogate markers of protection. VACSEL will, therefore, conduct longitudinal studies in three geographically distinct African countries of TB contacts who do or do not develop clinical disease, in order to identify the antigens, the cytokine profile and the markers of apoptosis that correlate with protection so that rational design and testing of vaccines can begin.
The overall objective is to acquire the information needed to allow the design of tuberculosis vaccines for trial in humans by the end of the project. This includes antigen selection, rates of transmission and identification of surrogate markers of protection so that volunteer studies can confirm the appropriateness of candidate vaccines before proceeding to large, lengthy protection studies. The specific objectives are:
1) to identify and follow cohorts of tuberculosis-exposed individuals in three geographically separate African countries
2) to transfer novel reagents and technology to these centres by training personnel
3) to identify antigens from M. tuberculosis recognised by T cells from exposed individuals who do and do not develop disease
4) to define cytokine profiles and markers of apoptosis associated with immunity in fresh, unstimulated, peripheral blood mononuclear cells, and in antigen-driven cultures.
VACSEL will transfer technology, reagents and training to three geographically distinct, high quality African field centres, which have already identified, or are now defining, cohorts of individuals who have been exposed to tuberculosis, and either do or do not develop overt disease. Preliminary studies at one of these centres show that 17% of these contacts may rapidly develop disease. One of the partners in the consortium has already stored peripheral blood mononuclear cells from such individuals. SSI has purified antigens from M. tuberculosis, and identified those that trigger strong T cell responses. Pilot studies with AHRI have indicated that the pattern of response to some of these antigens may predict resistance or susceptibility to TB, and it is crucial that this study is expanded and confirmed in other geographical locations. To identify the antigens recognised by protected individuals, lymphoproliferative responses to these antigens will be studied longitudinally over the course of the project. Supernatants from in vitro culture will also be used to assay cytokine production by ELISA. UCL will contribute a novel protocol for sensitive quantitative RT-PCR, which includes a method for rapid production of standards for any mRNA, and the ability to handle large numbers of samples. The method readily quantitates background cytokine mRNA expression levels in fresh, unstimulated, peripheral blood mononuclear cells from normal donors, and will be used to detect changes in background cytokine expression in the study cohorts, and the cytokine profile generated in vitro in response to the candidate antigens provided by SSI. mRNA will be stored, allowing further cytokines and markers of apoptosis to be studied as they become identified. This project will further strengthen the research and training capabilities of the three African centres, all of which are candidate sites for the eventual TB vaccine trials.
Year 1: a) Train personnel from the field centres. b) Identify cohorts. c) Start study.
Years 2 and 3: a) Continue longitudinal studies of cohorts. b) Expand repertoire of antigens and RT-PCR target mRNAs. c) Identify antigens that elicit responses in immune individuals, and the cytokines and markers of adoptosis associated with this response pattern. d) Recommendation for vaccine design, and surrogate markers suitable for pilot studies.
University College London
Department of Bacteriology, Windeyer Institute of Medical Sciences
46 Cleveland Street
W1P 6DB London
Tel: +44 20 7679 9311
Fax: +44 20 7679 8175