Enhanced protection against tuberculosis by vaccination with recombinant BCG over-expressing HspX protein

Immunization with Mycobacterium bovis Bacille Calmette-Guerin (BCG) did not induce adequate Th1 responses to the latency antigen, HspX of M. tuberculosis. To increase the immunogenicity and protective efficacy of BCG, a recombinant BCG strain over-expressing antigen HspX (rBCG::X) was constructed. The recombinant strain rBCG::X expressed high levels of both HspX protein in the cytosol and Ag85B protein in the cytosol and supernatant. Mice vaccinated with rBCG::X produced a more consistent and enduring protective effect against infection with M. tuberculosis, showing lower bacterial load in lung and less severe lung pathology, than the control mice vaccinated with BCG strain containing the vector pMV261. The long-term protection induced by rBCG::X was associated with significant increases in antigen-specific IFN-gamma to both HspX and Ag85B proteins, while PPD-specific IFN-gamma responses declined. Our results suggest that latency antigens of M. tuberculosis may be promising targets for developing more effective recombinant BCG strains to protect against TB.