Targeting the lung innate pathways during tuberculosis can improve vaccine-induced protection via Th17 responses in diversity outbred mice

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis (Mtb), infects approximately one-fourth of the world’s population. Inbred mouse models of TB do not reflect the pathological states and heterogeneity seen in human TB disease. Thus, we recently established a model of TB in diversity outbred (DO) mice, which displayed heterogeneity in inflammatory and protective responses following aerosol Mtb infection. In the current study, we show that DO mice vaccinated with M. bovis Bacille Calmette Guerin (BCG) are significantly protected upon Mtb HN878 infection, and protection is associated with the induction of transcriptional pathways involved in transforming growth factor B (TGF-β) and Toll-like receptor (TLR)-10 signaling. Targeting lung innate pathways in BCG-vaccinated DO mice using adjuvants also further improved protection upon Mtb infection by inducing genes associated with cellular responses to external stimuli, B-cell responses, as well as IL-17-producing CD4⁺ T-cell responses. Depletion of CD4⁺ T cells resulted in loss of vaccine-induced protection in DO BCG-vaccinated and adjuvant-treated Mtb-infected mice. Together, our new results show that innate targeting of the lung by activating TLR pathways could induce protective pathways in T cells that significantly improve upon the protection induced by BCG vaccination. Additionally, the DO mouse model of vaccination and Mtb infection can provide novel insights into immune pathways that are important for improving vaccine-induced protection against TB. IMPORTANCE Bacille Calmette Guerin (BCG) vaccination in genetically diverse outbred (DO) mice provides significant protection against Mycobacterium tuberculosis (Mtb) challenge. This protection induced pathways associated with transforming growth factor B (TGF-β) receptor complex, genes associated with lung repair, and Toll-like receptor (TLR)-10 pathway. The enhanced protection observed in BCG-vaccinated mice correlated with improved formation of B-cell follicles and IL-17-producing CD4⁺ T-cell responses. CD4⁺ T-cell responses mediated the enhanced protection in the lungs of DO mice vaccinated with BCG + adjuvant, as depletion of CD4⁺ T-cell responses reversed the enhanced protection. The DO mouse model of tuberculosis vaccination is a highly relevant model to probe mechanisms of vaccine-induced protection and provide novel insights into lung pathways that mediate protection. The study also found that genes associated with lung repair, including TGF-β receptor complex pathways, were induced in BCG-vaccinated Mtb-infected DO mouse lungs. The study suggests that the activation of lung innate pathways in BCG vaccination through the use of mucosal Amph CpG delivery, CD40L activation, and IL-10 neutralization could significantly enhance protection upon Mtb challenge.