Immunogenicity and safety of Mycobacterium tuberculosis culture filtrate proteins in non-human primates

The development of improved vaccines is considered a high priority in the effort to control tuberculosis (TB) world wide. Results from several studies performed in relevant animal models have demonstrated that Mycobacterium tuberculosis secreted antigens may represent major components of improved TB vaccines. To characterize further the M. tuberculosis secreted antigens as they relate to specific features important for vaccine development, rhesus macaques were immunized with either one of two different preparations containing M. tuberculosis culture filtrate (CF) proteins. These preparations differed in relative protein content and in the presence or absence of lipoarabinomannan. Animals received a total of three monthly intramuscular injections consisting of CF proteins resuspended in RIBI adjuvant and were tested for development of specific antibody and cellular proliferative responses. In addition, all animals were constantly monitored for local and systemic reactions as well as for the development of DTH reactions to intradermal tuberculin injection. Results from this study show that the two CF preparations are relatively safe and immunogenic in non-human primates. These two CF preparations differed in their ability to induce specific antibody responses, but were comparable in their ability to induce specific cellular proliferative responses. Induction of both humoral and cellular responses occurred even in presence of pre-existing antibodies directed against M. tuberculosis antigens. However, these responses appeared to be short-lived. Only one of the four animals produced interferon-gamma (IFN-gamma) in response to immunization with CF proteins. No DTH reaction to intradermal tuberculin injection was observed in any immunized animal. Although it is clear that additional studies are required to design strategies for the improvement of the immunogenicity of CF proteins, our observations support the currently accepted view that secreted protein-based preparations may represent promising vaccine candidates for TB.