Antigenic equivalence of human T-cell responses to Mycobacterium tuberculosis-specific RD1-encoded protein antigens ESAT-6 and culture filtrate protein 10 and to mixtures of synthetic peptides

The early secreted antigenic target 6-kDa protein (ESAT-6) and culture filt rate protein 10 (CFP-10) are promising antigens for reliable immunodiagnosi s of tuberculosis, Both antigens are encoded by RD1, a genomic region prese nt in all strains of Mycobacterium tuberculosis and ill: bovis but lacking in all ill. bovis bacillus Calmette-Guerin vaccine strains, Production and purification of recombinant antigens are laborious and costly, precluding r apid and large-scale testing. Aiming to develop alternative diagnostic reag ents, we have investigated whether recombinant ESAT-6 (rESAT-6) and recombi nant CFP-10 (rCFP-10) can be replaced with corresponding mixtures of overla pping peptides spanning the complete amino acid sequence of each antigen. P roliferation of M. tuberculosis-specific human T-cell lines in response to rESAT-6 and rCFP-10 and that in response to the corresponding peptide mixtu res were almost completely correlated (r = 0.96, P < 0.0001 for ESAT-6; r = 0.98, P < 0.0001 for CFP-10), More importantly, the same was found when ga mma interferon production by peripheral blood mononuclear cells in response to these stimuli was analyzed (r = 0.89, P < 0.0001 for ESAT-6; r = 0.89, P < 0.0001 for CFP-10), Whole protein antigens and the peptide mixtures res ulted in identical sensitivity and specificity for detection of infection w ith M. tuberculosis. The peptides in each mixture contributing to the overa ll response varied between individuals with different HLA-DR types. Interes tingly, responses to CFP-10 were significantly higher in the presence of HL A-DR15, which is the major subtype of DR2. These results show that mixtures of synthetic overlapping peptides have potency equivalent to that of whole ESAT-6 and CFP-10 for sensitive and specific detection of infection with i ll. tuberculosis, and peptides have the advantage of faster production at l ower cost.