Induction of CD8 T cells against a novel epitope in TB10.4: correlation with mycobacterial virulence and the presence of a functional region of difference-1.

Although infection with Mycobacterium tuberculosis (M.tb) induces a robust CD8 T cell response, the role of CD8 T cells in the defense against M.tb, and the mechanisms behind the induction of CD8 T cells, is still not clear. TB10.4 is a recently described Ag that is expressed by both bacillus Calmette-Guérin (BCG) and M.tb. In the present study, we describe a novel CD8 T cell epitope in TB10.4, TB10.4(3-11). We show that TB10.4(3-11)-specific CD8 T cells are induced at the onset of infection and are present throughout the infection in high numbers. TB10.4(3-11) CD8 T cells were recruited to the site of infection and expressed CD44, TNF-alpha, and IFN-gamma. In addition, TB10.4(3-11) CD8 T cells showed an up-regulation of FasL and LAMP-1/2 (CD107A/B), which correlated with a strong in vivo cytolytic activity. The induction of TB10.4(3-11)-specific CD8 T cells was less pronounced following infection with BCG compared to infection with M.tb. By using a rBCG expressing the genetic region of difference-1 (RD1), we show that the presence of a functional RD1 region increases the induction of TB10.4(3-11)-specific CD8 T cells as well as the bacterial virulence. Finally, as an M.tb variant lacking the genetic region RD1 also induced a significant amount of TB10.4(3-11)-specific CD8 T cells, and exhibited increased virulence compared with BCG, our data suggest that virulence in itself is also involved in generating a robust CD8 T cell response against mycobacterial epitopes, such as TB10.4(3-11).