Accelerating the preclinical development of effective vaccines for protection against Mycobacterium tuberculosis

The Bacille Calmette–Guerin (BCG) vaccine offers partial protection against tuberculosis (TB). Vaccines able to sufficiently contribute to global TB control are required urgently. The mouse model is an important tool for preclinical evaluation of TB vaccines, however protection in this model is not always predictive of efficacy in humans. TB is caused by various members of the Mycobacterium tuberculosis (MTB) complex. Differences in the host response to infection are known; however, incorporation of this diversity into in vivo studies is not viable due to the large number of animals required. Currently, vaccines are commonly evaluated against laboratory strains. The evidence of protection gained from these studies is likely to be incomplete. The ex vivo mycobacterial growth inhibition assay (MGIA) represents an alternative viable tool to perform head-tohead screening of vaccine-induced immunity. A murine splenocyte MGIA has been established. This thesis demonstrates the adaptation of the murine MGIA for use with lung cells, as a potential readout of lung immunity. Further, the MGIA was used to determine vaccine-induced growth inhibition against multiple MTB clinical isolates. Comparison of the MGIA and in vivo infection was performed for the first time using clinical isolates. Observations indicate that the MGIA may represent a tool to evaluate vaccines against the most prevalent MTB lineages. Further optimisation for other lineages is required. Evaluation of the biological processes underlying growth inhibition was performed by RNA-seq. Vaccine- and lineage-specific gene perturbations were identified. Comparison of correlates of growth inhibition in the MGIA and protection in an in vivo dataset revealed that the lung MGIA recapitulates several elements of in vivo transcriptional perturbation observed following infection. Collectively, these observations demonstrate that the MGIA warrants further development as a simplified model of ex vivo immunity to infection able to expediate and diversify preclinical TB vaccine testing.