A Bovine Adenovirus (BAdv) Expressing Mycobacterial Secreted Ag85B and a TLR-2 Stimulating Adjuvant Peptide Induces Robust Antigen Presentation In vitro and Improved Protection against Tuberculosis in Mice

Abstract

Abstract Human Adenovirus (HAdv) vectors expressing Mycobacterium tuberculosis (Mtb) derived antigens, have been tested as candidate boosters for BCG vaccine in animal models and Phase I human studies but failed to provide significant additional protection. Presumably, pre-existing immunity to HAdv among humans has been suggested to limit their efficacy as vectors. We earlier reported that novel bovine adenovirus (BAdv)-vectors induced robust T cell mediated immunity in mice and carried less risk of interference by human innate immunity. Thus, we evaluated BAdv vectors expressing Mtb derived antigen 85B and a novel TLR-2 activating peptide as booster vaccines for BCG in vitro and in mouse model for tuberculosis. Both mouse and human APCs (macrophages and dendritic cells) infected with BAdv-85B showed robust presentation of p25 epitope to T cells within 18 hrs of infection. BAdv-Ag85B-TLR2 was better than BAdv-85B in inducing antigen presentation. Antigen presentation by both BAdv-Ag85B and BAdv-Ag85B-TLR2 peptide were significantly decreased when DCs were derived from atg7 knockout mice or when 3-methyladenine was used for blockade, indicating that autophagy played a role during adenovirus-induced antigen presentation. Consistent with in vitro data, BAdv-Ag85B-TLR-2 and BAdv-Ag85B vaccinated mice exhibited reduced lung CFUs of Mtb by 1.5 log and 1.7 log respectively whereas BCG vaccinated mice could reduce CFUs by 0.95 log as compared to unvaccinated mice. In addition, the BAdv vaccines also protected spleens better than BCG suggesting improved protection against disseminated tuberculosis. Since BAdv can be given through mucosal route, we propose that they offer a novel mean to enhance lung and systemic immunity against tuberculosis.