Recombinant BCG Expressing LTAK63 Adjuvant induces Superior Protection against Mycobacterium tuberculosis

Area of Science:

• Immunology
• Vaccinology
• Microbiology

Background:

• Tuberculosis (TB) remains a global health challenge, necessitating improved vaccines.
• Bacille Calmette-Guérin (BCG) is the current TB vaccine but has variable efficacy.
• Adjuvants can enhance vaccine immunogenicity and protective efficacy.

Purpose of the Study:

• To develop an improved BCG vaccine against tuberculosis using an adjuvant.
• To construct and evaluate recombinant BCG (rBCG) strains expressing LTAK63 at different levels.
• To assess the immunogenicity and protective efficacy of rBCG-LTAK63_lo in a mouse model.

Main Methods:

• Construction of rBCG strains expressing LTAK63 at low (rBCG-LTAK63_lo) and high levels.
• Immunization of mice with rBCG-LTAK63_lo and wild-type BCG.
• Assessment of Th1 cytokines (IFN-γ, TNF-α) and IL-17 in the lungs via Real Time RT-PCR.
• Challenge of immunized mice with Mycobacterium tuberculosis (Mtb) and enumeration of colony-forming units (CFU).
• Histopathological analysis of lung tissues.
• Measurement of TGF-β levels post-challenge.

Main Results:

• Mice immunized with rBCG-LTAK63_lo showed increased Th1 cytokines and IL-17 in the lungs.
• rBCG-LTAK63_lo conferred a 2.0-3.0 log reduction in lung CFU compared to wild-type BCG after Mtb challenge.
• Protected mice exhibited reduced lung inflammation and protection against a 100-fold higher challenge dose.
• Immunization with rBCG-LTAK63_lo led to increased TGF-β post-challenge, correlating with reduced Th1/Th17 responses and pathology.
• rBCG-LTAK63_lo provided protection against a virulent Beijing isolate of Mtb.

Conclusions:

• Low-level expression of the LTAK63 adjuvant in BCG enhances pulmonary immune responses and protection against tuberculosis.
• A novel regulatory immune mechanism involving TGF-β is triggered, limiting pathology.
• The rBCG-LTAK63_lo strain represents a promising candidate for an improved tuberculosis vaccine.