Inhaled bacille Calmette–Guérin (BCG) provides a controlled human model to interrogate anti-mycobacterial immunity at defined time points, something not feasible in natural Mycobacterium tuberculosis infection. It also represents a promising mucosal vaccination route that outperforms intradermal (ID) BCG in animal models. We will present updated findings from two clinical trials in healthy adults: BCG-naïve and historically BCG-vaccinated participants received aerosolised BCG, with control groups of BCG-naïve participants given inhaled saline and previously vaccinated participants given ID BCG. Lung mucosal and peripheral blood responses were characterised longitudinally using single-cell RNA sequencing (scRNA-seq) and bulk T-cell receptor (TCR) sequencing.