A Potent Inhibitor of IL-10/STAT3 Axis Signaling Modulates Anti-Inflammatory Responses and Boosts Anti-Tuberculosis Immunity in rBCG30 Immunized Mice

Aims and Objectives: In the present study we tried to improve anti-TB immunity offered by 2nd generation rBCG30 vaccine. We attempted to bolster rBCG30 invoked anti-TB immunity in mice through modulation of the IL-10/STAT3 interaction mediated anti-inflammatory program. The study was aimed towards generating optimum activated APCs, early either after vaccination (with rBCG30) or infection (with Mtb), which can process and present mycobacterial antigens more efficiently to T cells. It was envisage that downmodulating IL-10/STAT3 signaling may improve immunity and protection offered by rBCG30 vaccine. Methods: A small molecule immunomodulator aimed at disrupting anti-inflammatory signaling orchestrated by IL-10/STAT3 axis was administered in rBCG30 immunized mice. The comparative expansion of pathogen permissive Alternatively Activated Monocytes/Macrophages/DCs (AAMs/AADCs) and Classically Activated Monocytes/Macrophages/DCs (CAMs/CADCs), the cells that resist establishment of successful Mtb infection, was profiled in both peritoneal and splenic compartment. To assess innate and adaptive T cell responses, splenocytes cytokine production was checked ex vivo using sandwich ELISA. We also checked polyfunctional T cell response, T cell memory response and comparative Th17/Treg cells expansion using flow cytometry. Finally, to assess the real time efficacy of the employed immunotherapeutic strategy, in vivo protection study was undertaken in BALB/c mice challenge with aerosolized Mtb (H37Rv). Results: The small molecule mediated inhibition of IL-10/STAT3 signaling was resulted in improved pro inflammatory immune responses in both post-vaccination and post-infection immunotherapy schedules. The improved immune profile in rBCG30 vaccinated and immunotherapy administered mice was accompanied with enhanced expansion of CAMs/CADCs, elevated production of polyfunctional T cells producing signature Th1 cytokines, long lasting CD4+ and CD8+ memory T cell response and balanced Th17/Treg cells ratio. Interestingly, post-infection, and not post-vaccination immunotherapy, was able to significantly reduce mycobacterial loads in spleen and lungs of experimentally infected mice. Conclusions: Small molecule mediated transient disruption of anti-inflammatory effectors, such as IL-10/STAT3, during vaccination or post infection with Mtb, may serve to enhance the efficacy of existing and forthcoming TB vaccines. The strategy can also be tested concomitantly with standard chemotherapy (either in vaccinated or unvaccinated host) to enhance the efficacy of therapeutic regimen and to reduce the treatment length.