Identification of Mycobacterium tuberculosis-specific genomic regions encoding antigens inducing protective cellular immune responses.

Comparative genomic studies have identified 11 regions of difference (RD1, RD4, RD5, RD6, RD7, RD9, RD10, RD11, RD12, RD13 and RD15) in Mycobacterium tuberculosis genome which are absent in all vaccine strains ofM. bovis BCG. The proteins encoded by genes predicted in these RDs could be useful as protective vaccines and/or exacerbate the disease process by inducing cellular immune responses involved in protection and pathogenesis of tuberculosis. In our studies, by using pools of overlapping synthetic peptides covering the sequence of putative proteins encoded by genes predicted in each RD, we have determined the cellular immune responses in relation to antigen-induced proliferation and secretion of the protective Th1cytokine IFN-gamma and the pathologic Th2 cytokine IL-10 by peripheral blood mononuclear cells of tuberculosis patients and healthy humans. It has been observed that peptides of RD1pool induced the highest antigen-induced proliferation and IFN-gamma responses, whereas the peptides of RD12pool and RD13pool induced the highest IL-10 responses. Furthermore, addition of RD12pool and RD13pool to peripheral blood mononuclear cells (PBMCs) cultures inhibited the RD1pool-induced secretion of IFN-gamma by PBMCs of healthy humans. These results suggest the relevance of RD1-encoded proteins in protection and RD12- and RD13-encoded proteins in pathogenesis of tuberculosis.