Only a minority of individuals with latent Mycobacterium tuberculosis (Mtb) infection (~5%) develop TB disease, typically pulmonary TB (PTB), due to the reactivation of dormant mycobacteria. There is growing genetic epidemiological evidence that PTB has a strong genetic component in humans, but the molecular basis of susceptibility to Mtb reactivation remains largely unknown. Candidate gene and genome-wide (GW) association studies have suggested that common variants play only a modest role in the genetics of PTB, or that their role is restricted to specific subgroups. We recently showed, by an unbiased GW linkage approach, that common variants of TOX, a gene involved in T-cell and NK-cell development, are associated with PTB in young patients with a short latency duration, in two ethnically different populations. Genetic factors other than TOX may also contribute to PTB, including rare variants of unknown genes. Our project will combine a focused in-depth dissection of the role of TOX in PTB, based on both human and mouse studies, with a GW approach investigating the role of rare variants in PTB. Study subjects will be recruited in Haiti, through the GHESKIO Center, to establish a large case/control sample (HIV-negative and HIV-positive), and a family-based sample with at least two PTB-affected siblings. We will conduct a comprehensive association study of PTB with TOX polymorphisms, and a GW search for rare variants in PTB patients, based on a combination of GW linkage and whole-exome sequencing studies. All variants consistently found to be associated with PTB will be validated immunologically, at the molecular and cellular levels with cutting-edge techniques. We will study the functional impact of previously identified variants located in the 3' region of TOX on T-cell immunity, both in vitro in human cells, and in vivo in mice. Mouse models will be used to investigate the role of TOX in T-cell responses to Mtb infection, together with analyses of endogenous T-cell responses in mice with T cell-specific TOX gene deletion. Our preliminary data indicate that TOX is strongly expressed in human CD4, Treg, NK, and yOT cells and in murine CD4 and Treg cells, and that the 3' end of TOX probably has regulatory activities, -further supporting the candidacy of TOX as a prime regulator of PTB immunity.
We aim to decipher the genetic variants accounting for the development of PTB, to provide both a long-awaited understanding of its pathogenesis and biomarkers for individuals at risk of PTB. These findings will have major implications for the definition of new prevention strategies (new vaccines and the optimization of clinical trials), and for the development of novel treatments aiming to restore deficient immune responses.
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