Enhanced protection conferred by mucosal BCG vaccination associates with presence of antigen-specific lung tissue-resident PD-1+ KLRG1− CD4+ T cells

BCG, the only vaccine licensed against tuberculosis, demonstrates variable efficacy in humans. Recent preclinical studies highlight the potential for mucosal BCG vaccination to improve protection. Lung tissue-resident memory T cells reside within the parenchyma, potentially playing an important role in protective immunity to tuberculosis. We hypothesised that mucosal BCG vaccination may enhance generation of lung tissue-resident T cells, affording improved protection against Mycobacterium tuberculosis. In a mouse model, mucosal intranasal (IN) BCG vaccination conferred superior protection in the lungs compared to the systemic intradermal (ID) route. Intravascular staining allowed discrimination of lung tissue-resident CD4+ T cells from those in the lung vasculature, revealing that mucosal vaccination resulted in an increased frequency of antigen-specific tissue-resident CD4+ T cells compared to systemic vaccination. Tissue-resident CD4+ T cells induced by mucosal BCG displayed enhanced proliferative capacity compared to lung vascular and splenic CD4+ T cells. Only mucosal BCG induced antigen-specific tissue-resident T cells expressing a PD-1+ KLRG1− cell-surface phenotype. These cells constitute a BCG-induced population which may be responsible for the enhanced protection observed with IN vaccination. We demonstrate that mucosal BCG vaccination significantly improves protection over systemic BCG and this correlates with a novel population of BCG-induced lung tissue-resident CD4+ T cells

Identification of antigens presented by MHC for vaccines against tuberculosis

Mycobacterium tuberculosis (M.tb) is responsible for more deaths globally than any other pathogen. The only available vaccine, bacillus Calmette-Guérin (BCG), has variable efficacy throughout the world. A more effective vaccine is urgently needed. The immune response against tuberculosis relies, at least in part, on CD4+ T cells. Protective vaccines require the induction of antigen-specific CD4+ T cells via mycobacterial peptides presented by MHC class-II in infected macrophages. In order to identify mycobacterial antigens bound to MHC, we have immunoprecipitated MHC class-I and class-II complexes from THP-1 macrophages infected with BCG, purified MHC class-I and MHC class-II peptides and analysed them by liquid chromatography tandem mass spectrometry. We have successfully identified 94 mycobacterial peptides presented by MHC-II and 43 presented by MHC-I, from 76 and 41 antigens, respectively. These antigens were found to be highly expressed in infected macrophages. Gene ontology analysis suggests most of these antigens are associated with membranes and involved in lipid biosynthesis and transport. The sequences of selected peptides were confirmed by spectral match validation and immunogenicity evaluated by IFN-gamma ELISpot against peripheral blood mononuclear cell from volunteers vaccinated with BCG, M.tb latently infected subjects or patients with tuberculosis disease. Three antigens were expressed in viral vectors, and evaluated as vaccine candidates alone or in combination in a murine aerosol M.tb challenge model. When delivered in combination, the three candidate vaccines conferred significant protection in the lungs and spleen compared with BCG alone, demonstrating proof-of-concept for this unbiased approach to identifying new candidate antigens