Mycobacterium tuberculosis is responsible for almost 2 million deaths annually. Mycobacterium bovis bacillus Calmette-Guérin, the only
vaccine available against
tuberculosis (TB), induces highly variable protection against TB, and better TB
vaccines are urgently needed. A prerequisite for candidate
vaccine Ags is that they are immunogenic and expressed by M.
tuberculosis during
infection of the primary target organ, that is, the lungs of susceptible individuals. In search of new TB
vaccine candidate Ags, we have used a genome-wide, unbiased Ag discovery approach to investigate the in vivo expression of 2170 M.
tuberculosis genes during M.
tuberculosis infection in the lungs of mice. Four genetically related but distinct mouse strains were studied, representing a spectrum of TB susceptibility controlled by the supersusceptibility to TB 1 locus. We used stringent selection approaches to select in vivo-expressed M.
tuberculosis (IVE-TB) genes and analyzed their expression patterns in distinct disease phenotypes such as
necrosis and
granuloma formation. To study the
vaccine potential of these
proteins, we analyzed their immunogenicity. Several M.
tuberculosis proteins were recognized by immune cells from
tuberculin skin test-positive, ESAT6/CFP10-responsive individuals, indicating that these Ags are presented during natural M.
tuberculosis infection. Furthermore, TB patients also showed responses toward IVE-TB Ags, albeit lower than
tuberculin skin test-positive, ESAT6/CFP10-responsive individuals. Finally, IVE-TB Ags induced strong IFN-γ(+)/TNF-α(+) CD8(+) and TNF-α(+)/IL-2(+) CD154(+)/CD4(+) T cell responses in PBMC from long-term latently M.
tuberculosis-infected individuals. In conclusion, these IVE-TB Ags are expressed during pulmonary
infection in vivo, are immunogenic, induce strong T cell responses in long-term latently M.
tuberculosis-infected individuals, and may therefore represent attractive Ags for new TB
vaccines.