Enhancing tuberculosis vaccine efficacy with a heterologous mRNA-ChAdOx1 prime-pull strategy targeting lung-resident memory T cells

IntroductionTuberculosis (TB) remains a leading cause of morbidity and mortality worldwide, and Bacillus Calmette–Guérin (BCG) offers inconsistent protection against adult pulmonary TB. We previously showed that homologous mRNA vaccination encoding the mycobacterial antigen PPE15 (mRNA.PPE15) enhanced immunogenicity but did not improve protection over BCG alone.

We hypothesised that a heterologous “prime-pull” strategy, systemic mRNA priming followed by mucosal adenoviral boosting, would enrich lung-resident memory T cells (TRM) and improve efficacy.MethodsFemale C57BL/6 mice received BCG prime followed by subunit regimens combining intramuscular mRNA.PPE15 and intranasal ChAdOx1.PPE15 in different administration orders, alongside homologous controls. Cellular responses in spleen and lung were quantified by intracellular cytokine staining after PPE15 peptides stimulation.

Intravascular staining was used to distinguish parenchymal (IV-) from vascular (IV+) cells and combined with tetramer staining to identify PPE15-specific CD4+ and CD8+ TRM-phenotype in the lung parenchymal following vaccination. PPE15-specific serum antibodies were measured by ELISA.

Protective efficacy was assessed four weeks after aerosol Mycobacterium tuberculosis (M.tb) challenge by lung and spleen CFU enumeration.ResultsHeterologous vaccination induced robust spleen CD4+ and CD8+ responses and PPE15-specific IgG.