Mycobacterium tuberculosis infected CBA/J mice can generate robust and protective responses to antigen Ag85 when delivered as a soluble protein, but fail to respond efficiently in the context of natural infection

In CBA/J mice, susceptibility to Mycobacterium tuberculosis ( M.tb ) is associated with low interferon-gamma (IFN-γ) responses to antigens (Antigen 85 (Ag85) and Early Secreted Antigenic Target-6 (ESAT-6)) that have been defined as immunodominant. Here, we asked whether the failure of CBA/J mice to recognize Ag85 is a consequence of M.tb infection or whether CBA/J mice have a general defect in generating specific T cell responses to this protein antigen. We compared CBA/J mice during primary M.tb infection, Ag85 vaccination followed by M.tb challenge, or M.tb memory immune mice for their capacity to generate Ag85-specific IFN-γ responses and to control M.tb infection. CBA/J mice did not respond efficiently to Ag85 in the context of natural infection or re-infection. In contrast, CBA/J mice could generate Ag85-specific IFN-γ responses and protective immunity when this antigen was delivered as a soluble protein. Our data indicate that although M.tb infection of CBA/J mice does not drive an Ag85 response, they can fully and protectively respond to Ag85 if it is delivered as a vaccine. The data from this experimental model suggest that the Ag85-containing vaccines in clinical trials should protect M.tb susceptible humans.