Recovery of recombinant proteins CFP10 and ESAT6 from Escherichia coli inclusion bodies for tuberculosis diagnosis: a statistical optimization approach

Synthesis of an Adjuvant-Free Single Polypeptide-Based Tuberculosis Subunit Vaccine that Elicits In Vivo Immunogenicity in Rats

A novel tuberculosis subunit vaccine specific for Mycobacterium tuberculosis dual antigens, culture filtrate protein-10 (CFP-10) and antigen 85B (Ag85B) conjugated with cholera toxin non-toxic B subunit (CTB), was expressed as a single polypeptide in high amounts and cost-effectively in Escherichia coli. The recovery and purification conditions for the recombinant fusion protein were established. This simple peptide vaccine required no exogenous adjuvant as it contained CTB, a potent immune modulator. The vaccine's physiochemical, structural, and immunological properties were determined using the in-silico tools. It was highly antigenic, non-allergenic, and non-toxic. Its BlastP search with human proteomes excluded the chances of autoimmune reactions. The tertiary structure model (3D) was validated by Ramachandran plot assessment. The 3D structure docking with Toll-like receptors, TLR-1, 2, 4, and 6, showed that the binding affinity between the vaccine peptide and TLRs was high, and their complex was stable, indicating a strong immune response. The in-silico immune simulation revealed the vaccine-induced both innate and adaptive immune responses. In-vivo validation of the immunogenicity of CTB.CFP10.Ag85B in Wistar rats revealed higher activation of IgG immune response compared to either antigen protein. Similar results were also obtained using the C-ImmSim simulation online server. A comparison of immunogenicity of CTB.CFP10.Ag85B with the only available TB vaccine, Bacillus Calmette-Guérin (BCG) or as a booster after vaccination of Wistar rats with BCG, indicated that the IgG levels were the highest in rats vaccinated with BCG, followed by a booster dose of CTB.CFP10.Ag85B fusion protein. The fusion protein would be a safe potential vaccine booster candidate in BCG-primed individuals against TB.

High-yield production of major T-cell ESAT6-CFP10 fusion antigen of M. tuberculosis complex employing codon-optimized synthetic gene

Translation engineering and bioinformatics have accelerated the rate at which gene sequences can be improved to generate multi-epitope proteins. Strong antigenic proteins for tuberculosis diagnosis include individual ESAT6 and CFP10 proteins or derived peptides. Obtention of heterologous multi-component antigens in E. coli without forming inclusion bodies remain a biotechnological challenge. The gene sequence for ESAT6-CFP10 fusion antigen was optimized by codon bias adjust for high-level expression as a soluble protein. The obtained fusion protein of 23.7 kDa was observed by SDS-PAGE and Western blot analysis after Ni-affinity chromatography and the yield of expressed soluble protein reached a concentration of approximately 67 mg/L in shake flask culture after IPTG induction. Antigenicity was evaluated at 4 μg/mL in whole blood cultures from bovines, and protein stimuli were assessed using a specific in vitro IFN-γ release assay. The hybrid protein was able to stimulate T-cell specific responses of bovine TB suspects. The results indicate that improved E. coli codon usage is a good and cost-effective strategy to potentialize large scale production of multi-epitope proteins with sustained antigenic properties for diagnostic purposes.