Individuals with latent tuberculosis infection display pulmonary airway enrichment and recall recruitment of CD4+ TRM with protective functional phenotypes

Tuberculosis (TB) remains a worldwide public health threat, in part because of the limited efficacy of current BCG vaccination. Respiratory infection with Mycobacterium tuberculosis (Mtb) is most often followed by the development of protective immunity that contains the pathogen, resulting in latent tuberculosis infection (LTBI). We previously introduced bronchoscopic challenge of LTBI individuals using instillation of purified protein derivative (PPD) of Mtb to model specific induced local recall responses in the human lung. Here, we examined phenotypic and functional aspects of human airway CD4+ T cell populations in LTBI that correlate with protection from Mtb in animal infection models. Baseline bronchoalveolar lavage (BAL) was enriched for CD4+ T cells expressing the KLRG-/CD69+ tissue resident-memory (TRM) phenotype. Both Th1 (CCR6-CCR4-CXCR3+) and Th1* (CCR6+CCR4-CXCR3+) CD4+ T cell subsets demonstrated polyfunctional IFN-γ+TNF-α+ cytokine responses in response to in vitro PPD stimulation. Bronchoscopic PPD challenge, although leading to less robust cellular recruitment than observed previously, preserved the predominance of KLRG1-CD69+ TRM and also of CD4+ T cells that displayed IFN-γ+TNF-α+ dual cytokine production in response to PPD. CD4+ T cells of both control and PPD challenged human lung segments displayed increased expression of the protective CD153 molecule; CD153 expression also correlated with increased cytokine polyfunctionality, particularly of polyfunctional IFN-γ+IL-2+TNF-α+ and IFN-γ+TNF-α+ dual-positive cells. These results support the utility of BAL studies in LTBI to model human correlates of protection from Mtb with potential applicability to the design and initial evaluation of novel approaches to TB vaccination.