Enhanced immune responses in mice to combined immunization with Mycobacterium tuberculosis Ag85A and DDA/MPL

The tuberculosis (TB) Bacillus Calmette-Guerin (BCG) vaccine, which is based on Mycobacterium bovis, has variable protective efficacy in humans; therefore, safe and effective vaccines are urgently required to prevent this disease. The antigen 85A from Mycobacterium tuberculosis (M. tuberculosis) is a prime target for immunity in the early phase of tuberculosis in various animal models. The purpose of this study was to confirm whether Ag85A could elicit protective immune responses in mice. Dimethyldioctadecylammonium (DDA), an adjuvant with Th1-promoting activities and monophosphoryl lipid A (MPL), an immunostimulatory component that has strong adjuvant activity for both cellular and humoral immune responses, has been used as the adjuvant to study the biological and immunological characteristics of tuberculosis proteins in the researches previously. The gene coding Ag85A (fbpA), was cloned into a pET-30a(+) prokaryotic expression vector, and the induced amino acid sequence corresponds to a 33 kDa protein, which was confirmed by mass spectrometry and western blots. Mice were subcutaneously immunized with Ag85A protein emulsified with DDA and MPL and the results showed that the 85A antigen, when combined with these adjuvants, elicited strong Ag85A-specific T-cell responses and humoral responses as compared with vaccination with BCG. Based on the fact that this vaccine combination induced strong antigen-specific immune responses, it is a prime candidate as a component of a future TB vaccine. Key words: Tuberculosis, Ag85A, prokaryotic expression, cellular immune response, humoral response.