# Mycobacterium tuberculosis antigen-containing exosomes reinforce BCG vaccine efficacy by augmenting long-term protection and memory response against experimental tuberculosis in BALB-C mice

## TL;DR

Exosomes containing M.tb. antigens boost BCG vaccine effectiveness by enhancing immune responses and reducing bacterial load in mice.

## Contribution

M.tb. antigen-containing exosomes are shown to enhance BCG vaccine efficacy through improved long-term protection and memory response.

## Key findings

- Exosomes boost Th-1 immune responses by activating CD4+ and CD8+ T cells.
- They significantly reduce M.tb. burden in lungs, spleen, and lymph nodes.
- Exosomes increase memory T-cell populations and elevate iNOS/Nitric oxide levels.

## Abstract

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M.tb.), affects one-third of humanity. Despite the availability of effective drug regimens, complete eradication of M.tb. remains challenging due to prolonged treatment duration. Additionally, MDR-TB and co-infection with HIV further exacerbate disease severity. The Bacille Calmette–Guérin (BCG) vaccine has shown inconsistent efficacy due to the absence of Th-1 antigens. Hence, there is a critical need for either a novel vaccine candidate or an efficient booster to enhance BCG’s prophylactic efficacy. In this study, in-house prepared M.tb.-infected alveolar macrophage-derived exosomes (Rv-Exo) and ESAT-6-containing exosomes (ESAT-6 Exo) were characterized based on size, purity, and pathogen-associated molecular patterns (PAMPs), and their epitope mapping was also performed. These M.tb. protein-containing exosomes (MPEs) were utilized for immunization, either alone or as a booster to BCG, and evaluated in BALB/c mice against experimental M.tb. challenge. Our results demonstrate that ESAT-6 Exo and Rv-Exo, either alone or as a BCG booster, enhanced Th-1-biased immune responses by activating CD4+ and CD8+ T cells, increasing memory T-cell populations, and significantly reducing the M.tb. burden in the lungs, spleen, and lymph nodes of infected mice. These findings highlight the potential of MPE as a promising strategy against TB especially in the BCG-vaccinated population.

The M.tb. antigen bearing exosomes (Rv-Exo and ESAT-6 Exo) deliver antigen by fusion or endocytosis to boost BCG efficacy. They induce functional T-cells population, Th-1 skewed immuneresponse, effector/central CD4/CD8 T-cells memory, elevate iNOS/Nitric oxide, and reduce bacterial-burden in lungs, spleen and lymph nodes at twelve-weeks post-challenge (TWPC) in murine model.Scientific diagram summarizing an experimental study on mice immunized with exosomes and BCG variants, illustrating immunization routes, organ involvement, immune cell activation, exosome uptake by macrophages, antigen presentation, and downstream T and B cell responses following mycobacterial challenge, with a central focus on reduced mycobacterial burden and improved histopathology.

The M.tb. antigen bearing exosomes (Rv-Exo and ESAT-6 Exo) deliver antigen by fusion or endocytosis to boost BCG efficacy. They induce functional T-cells population, Th-1 skewed immuneresponse, effector/central CD4/CD8 T-cells memory, elevate iNOS/Nitric oxide, and reduce bacterial-burden in lungs, spleen and lymph nodes at twelve-weeks post-challenge (TWPC) in murine model.