Novel Recombinant BCG Coexpressing Ag85B, ESAT‐6 and Rv2608 Elicits Significantly Enhanced Cellular Immune and Antibody Responses in C57BL/6 Mice

Abstract

Tuberculosis (TB) remains an enormous global health problem, and a new vaccine against TB more potent than the current inadequate vaccine, the Bacille Calmette‐Guérin (BCG), is urgently needed. BCG has proven to be an effective recombinant delivery vehicle for foreign antigens because of its ability to induce long‐lived specific humoral and cellular immunity. Experimental evidences have revealed that Ag85B, ESAT‐6 and Rv2608 are important immunodominant antigens of Mycobacterium tuberculosis and are all promising vaccine candidate molecules. In this study, we have constructed a novel recombinant BCG (rBCG) expressing fusion protein Ag85B‐ESAT6‐Rv2608 and evaluated the immunogenicity of rBCG in C57BL/6 mice. Results show there is strong TB‐specific CD4+ and CD8+ T lymphocytes proliferative response in mice immunized with rBCG vaccine, especially the cytotoxic CD8+ T cells playing an important role in protection against TB. And rBCG immunization has induced a significantly strong Th1 immune response, characterized by the increased ratio of IgG2b/IgG1. Results also show that rBCG immunization could increase the secretion of Th1 cytokines such as TNF‐α and IL‐2 and could decrease the secretion of Th2 cytokine IL‐10. Moreover, it was shown that rBCG immunization induced a strong humoral response in mice, characterized by the elevated IgG titre. Therefore, we conclude that this rBCG immunization could increase both cellular immune response and antigen‐specific humoral response significantly as compared to BCG immunization in mice. The above results illustrated that rBCG::Ag85B‐ESAT6‐Rv2608 is a potential candidate against M. tuberculosis for further study.

Recombinant BCG: innovations on an old vaccine. Scope of BCG strains and strategies to improve long-lasting memory

“…Some rBCG vaccines designed over the past 5 years combined the ability to generate strong immune responses to Ag85 proteins using the antigen ESAT-6 (47, 52, 55). Of these studies, only one addressed protection and memory development.…”

“…As previously stated, vaccine construction over expressing proteins of the Ag85 Complex seem to have better protection efficacy than BCG, while rBCG–ESAT-6 induced protection similar or even inferior to BCG. However, using combined epitopes from proteins of the Ag85 complex or other proteins and ESAT-6 improved macrophage activation and antigen presentation (55), and strong humoral and cellular immune responses were induced (47), although protection or memory generation was not addressed.…”

Association of ESAT-6/CFP-10-induced IFN-γ, TNF-α and IL-10 with clinical tuberculosis: evidence from cohorts of pulmonary tuberculosis patients, household contacts and community controls in an endemic setting

“…Several studies have suggested that ESAT-6, CFP-10 and/or ESAT-6/CFP-10, alone or in combination with other proteins or BCG, induce strong protective T cell immunity during Mtb infection, especially in a murine model of TB [11,13,14,[27][28][29]. These reports have led to extensive research to realize the potential of these proteins as vaccine candidates [29][30][31][32][33][34]. Conversely, a substantial body of evidence indicates that these proteins are virulent factors involved in the pathogenicity of Mtb [23,[35][36][37][38].…”

Vaccines for TB: Lessons from the Past Translating into Future Potentials

“…The SO2 vaccine presents several key antigens from M. tb which have been shown to be crucial in conferring protection compared to BCG. The ESAT-6 antigen, for example, was shown to be highly immunodominant in a M. tb challenge study conducted in guinea pigs which was not found in BCG vaccination [54–56]. Therefore, the use of live attenuated M. tb as vaccine delivers a potential alternative.…”