Enhanced Immune Responses Against Mycobacterium tuberculosis Through Heat-Killed BCG with Squalene-in-water Emulsion Adjuvant

Abstract

The increasing challenge of drug-resistant tuberculosis (TB) calls for the development of innovative therapeutic strategies, highlighting the potential of adjunctive immunotherapies that are both cost-effective and safe. Host-directed therapy (HDT) using immunomodulators shows promise in enhancing treatment efficacy by modulating immune responses, thereby shortening the duration of therapy and reducing drug resistance risks. This study investigated the immunomodulatory potential of combining Heat-killed Bacillus Calmette-Guérin (hBCG) with a Squalene-based oil-in-Water Emulsion (SWE) adjuvant against TB. The therapeutic efficacy of the hBCG-SWE regimen was assessed in a guinea pig model infected with Mycobacterium tuberculosis (M. tb). Furthermore, the impact of hBCG-SWE on TNF-α and MCP-1 production was evaluated in RAW264.7 macrophages, examining the role of TLR2/4 and MyD88 signaling pathways using ELISA, both with and without specific inhibitors. Our findings revealed that hBCG-SWE significantly enhanced TNF-α and MCP-1 production compared to hBCG alone, indicating activation through TLR2/4 and MyD88-dependent pathways. In guinea pigs, hBCG-SWE administration led to notable reductions in lung pathology and spleen bacterial loads versus control groups. These results highlight the capacity of hBCG-SWE to boost innate immunity and provide robust protection against M. tb. Future research should focus on evaluating the ability of hBCG-SWE to shorten conventional chemotherapy and exploring ways to amplify its immunomodulatory efficacy through advanced formulation techniques.