Background: Despite increased global efforts, Tuberculosis (TB) remains the biggest killer amongst infectious diseases today. Due to the rise of multi-drug resistant strains and the absence of effective vaccines, the search for correlates of protection has become a major objective in TB research, to enable the development of novel and effective vaccines. Surprisingly, the nature of the lung mucosal proteome during TB infection is barely known, as most studies have only characterised a small subset of cyto- and chemokines, thus leaving the possible involvement of the majority of the lung mucosal proteome in the dark.
Methodology: In this first-in-mankind clinical study, we used a controlled human lung-challenge model to focus on neglected basic immunobiological aspects of Mycobacetrium tuberculosis (Mtb) infection in the lung. Bronchoalveolar lavages (BAL) were performed on patients with different susceptibility profiles, ranging from patients with presumed sterilising immunity, to those with latent TB infection, to patients with one or more episodes of active TB. BAL samples were taken both at baseline and after a three-day challenge with either live Bacillus Calmette–Guérin (BCG) or purified protein derivative (PPD). The mucosal cellular immune response was characterised using in-solution tryptic digestion and LC-MS/MS measurement on a Q Exactive mass spectrometer.
Findings: Overall, 3650 protein groups were identified in BAL fluid. Both challenges with BCG or PPD challenge induced dysregulation of the mucosal proteome compared to the baseline sample. However, PPD challenge resulted in twice as many dysregulated proteins than BCG challenge. Furthermore, patients from the four patient groups responded differently towards the both challenges according to their previous exposure to Mycobacterium tuberculosis.
Conclusion: Intra-lung challenge with PPD induced stronger mucosal immune responses compared to BCG challenge. We propose this proteomic approach to monitor intra-lung challenges with different vaccines, ultimately to enable improved design of effective vaccines and therapeutic interventions.