Vaccine candidates are emerging but the time and cost of TB clinical trials prohibits their evaluation. Surrogate markers are needed. Cells from carefully followed-up contacts who do or do not develop disease are being studied for cytokine expression by RT-PCR in three African centres. VACSIS will add a fourth centre, upgrade technology to real time RT-PCR, and study markers of apoptosis that play a role in immune response regulation in TB. Meanwhile, the patients’ TB strains will by typed for polymorphisms in DNA repair genes, and this will be related to disease severity, transmission and immunology.
The objective is to study blood mononuclear cells (and M. tuberculosis strains when available) from index cases and contacts who do or do not subsequently develop disease, and from community controls, in four genetically distinct African centres. With this material, the consortium will:
1) define markers of apoptosis associated with immunity to TB in unstimulated peripheral blood mononuclear cells and in cultures driven by a range of TB antigens in vitro
2) relate polymorphisms in DNA repair genes of the TB strains to disease severity, transmission and immune response
3) enhance the molecular immunology capacity of southern laboratories to enable them to adopt emerging technologies
4) encourage south-south collaboration of partner institutions
5) provide necessary immununological data, training and laboratory infrastructure for subsequent southern-led tuberculosis vaccine trials.
VACSIS is a sister study to VACSEL which has transferred technology, reagents and training to three geographically and genetically distinct African laboratories that have already identified and recruited cohorts of index cases, community controls and contacts who do or do not develop disease during follow-up. Peripheral blood mononucelar cells, cDNA and TB strains from these cohorts have been, and continue to be, banked. Currently VACSEL uses quantitative SYBR green-based RT-PCR to measure expression of a range of cytokines in fresh unstimulated cells, and in cells incubated in vitro with several antigens from TB, so that response patterns can be correlated to subsequent resistance or susceptibility to disease. VACSIS will establish a cohort in the laboratory of a fourth southern partner, and enhance the technology and training in all four centres. One partner has shown that the RT-PCR method can be transferred directly to the newly developed ABI PRISM 7000 SYBR green-based real time PCR system with enormously enhanced throughput and precision. This will enable expansion of the number of markers studied at all four centres, notably a large range of molecules involved in the control of T cell and macrophage activation and apoptosis. This will maximise the potential for identifying clinically useful correlates of immunity, and set up the southern partners to easily study other markers as they are identified. Meanwhile another partner has discovered polymorphisms of DNA repair genes that might enable TB to resist immunity and drugs. The bank of strains will therefore be typed by VACSIS, which provides the unprecedented possibility of relating findings to clinical outcome, transmission and immunology. VACSIS will encourage collaboration and networking between the African partners, and develop them as future vaccine trial sites.
1) Detect markers of apoptosis and T cell activation by RT-PCR in banked
cells from TB contacts.
2) Establish a contact cohort in the laboratory of a fourth southern partner.
3) Detect point mutations in banked TB strains from index cases.
4) Correlate immunological, RT-PCR, strain analysis and clinical data.
5) Identify immune correlates useful in TB vaccine trials.
University College London
Department of Medical Microbiology
46 Cleveland Street
W1P 6DB London
Tel: +44 20 7679 9311
Fax: +44 20 7636 8175