Enhancing Mycobacterium tuberculosis-Ag85B immunogenicity by fusing with human Fcγ1 (Ag85B:hFcγ1)

Tuberculosis (TB) is still a life-threatening infection. Mycobacterium tuberculosis (Mtb) Ag85 is the most potent immunogenic factor for introducing protective vaccines against TB. To enhance its immunogenicity, Mtb Ag85B was fused to the Fc fragment of human IgG1 to produce Ag85B:hFcγ1 and its immunogenicity was assessed in a mouse model. The Ag85B:hFcγ1 was designed and made in the Pichia pastoris expression system. Then, the production and purity of Ag85B:hFcγ1 were confirmed using ELISA and Western blotting. Co-localisation assay showed that Ag85B:hFcγ1 can be localised with hFcγRI (CD64), facilitating a proper Th1 response. Immunisation assays in a mouse model showed a high IFN-γ production as the hallmark of cell-mediated immunity (CMI) in the sera of the treated animals compared with the control ones (p = 0.02). However, the concentration of IL-17 did not reach the sensitivity of the assays. Functional co-localisation revealed that the fused hFcγ1 with Ag85 can bind to CD64 and induce cross-presentation toward Th1 responses by producing higher IFN-γ. In conclusion, Ag85B:hFcγ1 with high glycosylation seems more immunogenic than our previous studies Mtb multistage and Fc fusion proteins-multi molecules. APC targeting was used to favour cross-presentation using the Fc tag.